Draft
World Meteorological Organization
FORMAT TO EXCHANGE OPERATIONAL
AND ARCHIVED DATA ON SEA ICE
(CONTOUR-2)
Content
- Introduction
- Lay-out of the format
- Header-record of the ice
chart
- Coding of geographical
coordinates
- Content of ice chart, coding
of ice characteristics
- Coding of ice characteristics
in the main zones
- Coding of the boundaries of
the main zones
- Description of the zones
delineated by additional characteristics
- A section of linear objects
- A section of
point objects
- A section of
the ice drift
- Coding of data
of en-route observations
- Text report
- Dissemination
of operational ice information, exchange of archived data
Annex 1
CODE TABLES
- Code table 1
Observation methods and means
- Code table 2
Ice distribution
- Code table 3
Stage of development
- Code table 4
Forms of floating ice
- Code table 5
Additional generalized characteristics
- Code table 6
Linear objects of the ice cover
- Code table 7 Point
objects of the ice cover
- Code table 8
Dynamics and deformations of the ice cover
- Code table 9
Total and partial concentration
- Code table 10 Ice
compacting (pressures)
- Code table 11
Width of leads
- Code table 12
Snow depth
- Code table 13
Surface relief of multiyear ice
- Code table 14
Relative area of polluted ice
- Code table 15
Stage of melting
- Code table 16
Specification of icebergs (as established by the International Ice Patrol
Service)
- Code table 17
Relative number of icebergs
Annex 2
TERMS ABSENT IN THE WMO SEA-ICE NOMENCLATURE AND INCLUDED TO CODE TABLES
Annex 3
EXAMPLE OF CODING A COMPOSITE ICE CHART (link to chart)
Annex 4
INFORMATION PROPERTIES OF REMOTE SENSING MEANS
- Satellite observations in the visible
range
- Satellite observations in the IR range
- Ice observations in the microwave band.
- Visual observations from aircraft
- Combined use of information
- Tables section
- Table 1 Possibility and accuracy of
determining age (thickness) of the ice floes (cm)
- Table 2 Possibility and accuracy of
determining the main generalized characteristics (tenths or conventional
scale units).
- Table 3 The
accuracy of determining the boundaries, ice drift vectors, the
possibility for detecting ice formations.
Annex 5
A PROPOSAL FOR CODING THE POSITIONS OF THE POINTS
IN THE RECTANGULAR COORDINATES, RATHER THAN IN THE GEOGRAPHICAL COORDINATES
The SIGRID-2 format was
approved by WMO CMM and recommended for use by all national ice services (a
letter of Mr. J.Rasmussen, Director WWWD, No. 42.276/W/MA/MS-SI of July 29,
1994). This format allows addressing the goals of the World Climate Program,
but not the objectives of providing direct support to shipping and other
activities at seas, as well as scientific studies of polar areas. Hence all
national ice services use their own contour formats for practical application.
Increased international
transport shipping in the Arctic and the Antarctic, joint experiments in these
regions within the framework of international programs and agreements make a
more detailed exchange of operational and regime information (as compared to
SIGRID-2) quite important. Hence the development of one common international
format for such an exchange is equally significant.
The proposed format
Contour-2 is to be used for transfer of data on ice situation in the seas and
the oceans from the processing centers of different levels to users
(icebreakers, ships, drilling platforms), creation of databases and sea-ice
data exchange between the national and international processing centers and
databases.
The format provides for
storage and transfer of all data on the ice charts compiled using the WMO
Sea-Ice Nomenclature and allows the list of variables to be extended by using
additional letter designations for their identification. The accuracy of
delineating the boundaries of the zones and the position of linear and point
objects is completely preserved. It is envisaged to use coding of only available
information without the term "undetermined/unknown" and other methods
for reducing the volume of letter-digital ice charts.
The individual (area and
en-route) and composite ice charts coded in this format can be displayed on
computer without any preliminary preparation (with hard copies printed or
plotted) or converted into any rectangular grid.
Each individual or a
composite ice chart consists of nine sections composing one file:
- header-record, also including the boundaries
of data acquisition.
- sets of ice characteristics in the main
zones with the assigned ordinal numbers and of the information points of
the zones,
- boundaries of the main zones,
- additional zones,
- linear objects,
- point objects,
- ice drift,
- data of en-route observations.
- text message.
Each
section begins with the corresponding text constant which is situated on a
separate line: CONTOUR-2, IF, BOUND, ZONE, LINE, POINT, DRIFT, ROUTE, TEXT.
If there is no information
on some section or other, its constant is not indicated. The constant END which
is written on a separate line, is an indication of the
end of the letter-digital ice chart.
3. HEADER-RECORD OF THE ICE CHART
All modern methods of ice
observations have limitations regarding the characteristics to be determined
and accuracy. Hence for a sufficiently complete description of the ice cover
properties it is necessary to use a complex of means operating in different
ranges of electromagnetic waves on different media and with respectively
different spatial and temporal resolutions, different accuracy and reliability.
Therefore, practically all ice centers issue composite ice charts.
The methodological
principle for compiling a composite chart of ice situation is to use all
available information taking into account the information properties and the
accuracy of geolocation of data of each specific instrument. Individual charts
serve as input information for operational composite ice charts. They are based
on TV (IR in wintertime) satellite imagery, airborne radar and SLAR imagery,
visual ice observations (in the form of en-route charts), as well as shipborne
data, data from polar stations and automated ice stations prepared for use.
Each file of an individual
or a composite ice chart recorded on magnetic tape or transmitted via
communication channels begins with the header-record. As current information of
the composite chart which is constantly updated, can contain data of varying
individual charts in its separate parts based on different remote sensing
means, information in the header-record should provide the possibility to
determine the date, means and methods of information collection. The
header-record is written in the following format:
CONTOUR-2
AAFF
f......f;
NNNN
MMMMLLLLL1
MMMMLLLLL2 MMMMLLLLL3 MMMMLLLLL4 MMMMLLLLL1
YYMMDD
YYMMDD
MAP
PPrn1
CCCCC1 BBBB YYMMDD /MMMMLLLLL/
.....
......
PPrnn
CCCCCn BBBB YYMMDD /MMMMLLLLL/
LIMIT
MMMMLLLLL
MMMMLLLLL ........ MMMMLLLLL: MMMMLLLLL
........
ROUTE
PPrn
CCCCC BBBB YYMMDD
MMMMLLLLL
MMMMLLLLL ......... MMMMLLLLL
9999999999
where
AA - originating country;
FF - originating Service (institution);
f..f - type of information indicated on the ice
chart, coded by the constants:
- OBSERVATION - data of direct observations,
- CALCULATED - calculated data,
- FORECAST - prognostic chart,
NNNN - ordinal or archived No. of the
chart (defined by the National Center or institution),
MMMMLLLLL with indices 1 - 4 - geographical coordinates (degrees and
minutes of latitude and longitude) of the rectangular which contours the
observation region most closely,
YYMMDD with indices 1 and 2 - year, month and date of the start and end
of the observations used to construct the chart or the forecasting period.
After the MAP constant
which is written on a separate line:
PP - methods and means of observations
(code table 1), r - meaningful ground resolution digit in m, n
- power indicator 10.
Thus the resolution of each
remote sensing means is determined by the expression R=r10^n. For
example, the airborne radar survey with a ground resolution of 7 m is coded as AR70,
satellite observations in the IR range with a resolution of 1 km as PI113.
CCCCC - type of satellite (NOAA. METEOR, etc.) or aircraft,
BBBB - No. of the turn or the ice reconnaissance flight,
YYMMDD - date of the survey or receiving the satellite image (but not
the date of issuing an individual chart based on these data),
/MMMMLLLLL/ in symbols / / - geographical coordinates of the information
point within the observation region of the given individual chart.
After the constant LIMIT the geographical coordinates of the
turning points of the general boundary of the composite chart and boundaries of
the individual charts are enumerated.
The general boundary of a
composite or individual chart should be closed (the first and the last points
are repeated). Its description includes the points of joining of the boundaries
of zones and for a composite chart also the points of joining of the boundaries
of the individual charts. Separate segments of the boundaries are separated by
the symbol : .
Thus a system of closed
polygons with the information points is formed. It allows us to determine for
each part of the ice chart the date, means and methods of observations and
therefore make conclusions about the completeness, reliability and accuracy of
data presented on the chart and use them as input information for producing the
calculated and prognostic ice charts.
If data of airborne visual
observations, including profile observations by means of the radar thickness
meter and a laser profiler were used for issuing the chart, then the subsection
ROUTE is added to the header-record. In this subsection the information
point is not given on the line with the description of the observation means
and date, but on the new line the geographic coordinates of the turning points
of the route are enumerated.
The header-record of an
individual chart includes only one date of observation or receiving satellite
information and one information point (observations are uniform over the entire
area of the chart).
In the header-records of
the calculated and prognostic charts the sections MA and ROUTE, including the constants themselves
are omitted.
YYMMDD1 for the calculated charts is the
date of the start of observations which as a result of calculations are given
for the moment YYMMDD2. This is thus the date from which information on
the chart becomes old. For prognostic charts: YYMMDD1 - date of
preparing the forecast, YYMMDD2 - date when according to the forecast
the ice cover attains the predicted state.
The section LIMIT of the calculated and prognostic
charts enumerates the coordinates of only the external boundary of the ice
chart including the joining points of the boundaries of the zones.
The header-record of the
ice chart can be used as a base file of the ice chart identifiers allowing
retrieval of required information by region, observation time and means at the
requests of users.
4. CODING OF GEOGRAPHICAL
COORDINATES
The position of the
boundaries of the zones, linear and point objects is governed by their
geographical coordinates (degrees and minutes of latitude and longitude). Two
methods of longitude indication are used. According to the first traditionally
widespread method, in particular for all geographical topographic and base
charts, reading of longitudes is from the
In view of desirability to
reduce to the maximum the volume of coded information, especially, for
transmitting via the communication channels, as well as of the possibility to
use computers for coding and decoding, the description of longitudes in the
CONTOUR-2 format is only in the eastern direction from 0° to 360°. For each
point there is one nine-digit group where the first 4 digits are degrees and
minutes of latitude and the last five digits - degrees and minutes of
longitudes. Thus the coordinates of one point are described by only 9 digits
and not by 10 digits and one symbol. That is, the volume of coded information
is 10% reduced. For example, the point 75°37'N 103°28'W would be coded as 75377
10328 according to the first version and in the CONTOUR-2 format as 753725632.
If greater accuracy in
describing the coordinates (drift vector, large-scale charts of the unloading
sites on fast ice, ice situation in the vicinity of the drilling platforms,
etc.) is required, the format allows latitude to be coded by five digits by
increasing the number of digits up to 11 in the group with an accuracy up to
0.1', not even mentioning this in the text.
5. CONTENT OF ICE CHARTS, CODING OF
ICE CHARACTERISTICS
All ice charts compiled
from data of direct observations can be subdivided into 3 classes; large-scale
charts and plans, operational ice charts and review ice charts. Large-scale
charts and plans are based on data of high resolution remote sensing means with
the aim of a maximum detailed depiction of the ice cover state along the route
of icebreakers, convoys and separate vessels. Such charts mainly consist of the
ice formations which are important in terms of navigation (giant and sometimes
vast floes of old or thick first-year ice, leads and fractures, stamukhas,
icebergs, etc.). Only parts of sea surface where ice cakes and small floes and
ice floes less than 100 km in diameter were observed,
are depicted as zones of different total and partial concentration. By the term
"zone" one understands closed space on the chart within which the
values of all characteristics of the ice cover are assumed equal.
The operational ice charts
are to be used by navigators and the headquarters of marine operations for
supporting an escort of ships through the ice zones, studies of the ice regime
of the seas, as well as for subsequent preparation of the calculated and
prognostic ice charts. Unlike the large-scale charts, the operational charts
mainly depict zones of ice of varying concentration, age categories, forms,
surface structure, melting stages, etc. Of separate ice objects the operational
charts show: giant ice floes, leads and fractures, ridged ice and pressure
ridges, stamukhas, icebergs, drift divides and drift vectors.
The review ice charts allow
the general state of the ice cover over the area of the entire
The CONTOUR-2 format
provides coding with the aim to create the databases and transfer all listed
types of charts to users via the communication lines.
Each variable
(characteristic) of a zone or an ice object is coded by a two-letter
identifier. The first letter defines its belonging to some information block or
other (code table) and the second - a specific variable value, i.e. the term
from the WMO Nomenclature defining it. Then the code numbers of relative areas, estimates in conventional units or true values (size,
thickness, azimuth, etc.) are reported. Thus the proposed system for coding ice
characteristics clearly separates designation of notions and quantitative
characteristics.
6. CODING OF ICE CHARACTERISTICS IN
THE MAIN ZONES
By the main zones we mean
zones delineated by total concentration and age categories (studies of
development). The section begins with the constant INF on a separate
line. The variables and their numerical values of one or several zones
identified by the main characteristics, are described
on separate lines and are written in the following format:
=nnnCPffSPffFPffZPff ....... SPff:FPffZPffZPff
/MMMMLLLLL: ......
....
MMMMLLLLL/
where:
= - a symbol defining the beginning of the record of a set of ice
characteristics, nnn - the ordinal number of the set of characteristics;
C, S, F, Z - identifiers of separate blocks (code tables);
P with the corresponding indices are identifiers of specific variables
in tenths of the total area of the zones or in arbitrary units of the
corresponding scales;
: - a separating symbol after which data on the forms and additional
characteristics refer to the ice of all age stages;
/...... / - symbols / / restricting the description of the geographical
coordinates of the information points of the zones with a given set of ice characteristics;
MMMMLLLLL - geographical coordinates of the information points which are
separated from each other by the symbol :.
If in small zones the
conventional designations cannot be placed, then after the information point of
such a zone, the coordinates of the drawing point can be indicated, i.e. of the
point where these conventional designations should be depicted (on the shore,
beyond the boundary of data collection or in the adjacent extensive zone). At
displaying or plotting the chart, the information point and the point of
drawing are connected by a direct line. The information point and the point of
drawing are separated by a gap.
The description of a set of
variables begins with the identifier characterizing ice distribution (code
table 2). After the identifiers CW and CU no characteristics
are given and then the coordinates of the information points of the zones where
open water was observed or of the zones where observations were not made due to
weather conditions or other reasons are reported. After CI the total ice
concentrations can be given. In this case this is also partial iceberg
concentration. Partial concentration is not usually large (less than 1/10). It
is coded using common indications of total and partial concentration: at partial
concentration <5/100 ff=0, at large concentration ff is given
in tenths according to code table 9. At instrumental observations, if
partial concentration of icebergs is determined with an
accuracy up to 1/100 and less than 1/10, the code table 9 provides a
possibility for indicating its accurate value. Then the identifier FI
(iceberg size) and the numerical value of the variable are reported according
to table 16 or by a two-digit number in hundred meters without a distinguishing
letter "T". Even if a relative area of icebergs and their mean
size are determined, it is very important from the viewpoint of shipping to
know their relative amount per unit area and distribution over the sea which
determines the probability of encounter. Therefore it is also recommended, if
possible, to indicate in addition to relative area and mean size the relative
number of icebergs in the delineated zone. For this purpose the identifier ZI
and code table 17 are used. For example:
CI02FI25ZIT5
- in the zone "iceberg
water" the relative area of icebergs is 2%, mean size is 2.5 km, the
number of icebergs within a 20 km radius is 9-16 or mean distance between
icebergs is 5-7 miles.
Let us once again note that
identifiers and their relative values are only used for those variables which
are observed.
After CT total ice
concentration (code table 9) is given. If ice distribution within the
delineated zone (or zones) is non-uniform, then after total concentration the
identifier CS (strips, patches) and concentration are given. For example,
=nnnCT40CS60
- that is in the zones with a set of
characteristics nnn total concentration is 4/10, concentration in strips and
patches is 6/10.
After the identifier CF (fast
ice) total concentration is not given.
Then after CTff and CF
stages of development and partial concentration of the observed age stages are
recorded beginning from the most old ice. If ice of
land origin (icebergs) was observed in the drifting or fast ice, the description
of the age categories begins from them. Single (separate) icebergs are not
included into the description of the main zones, but are coded as point
objects*.
If mean ice thickness of
some age category is determined in the zone, then after the age stage category
and partial concentration the identifier SV is given and then a two-digit value
of the ice thickness in decimeters. For example,
SK40SV11 - medium first-year ice whose partial
concentration is 4/10, the measured mean thickness is 110 cm.
Sometimes, the remote
sensing means and observation conditions do not allow subdivision of ice
belonging to different main development stages (nilas, young, first-year, old). In this case a double identifier can be
written and then total concentration of this ice. For example,
SISW40 - thin and grey-white first-year ice of total partial concentration 4/10.
If some ice in the zone can
be estimated as ice of a definite age stage and more old, then after the
identifier of this initial age stage the SX identifier is written, and then
partial concentration of this ice. For example,
SKSX80 - medium first-year and more old ice of total
partial concentration of 8/10.
If only one age stage is
indicated (uniform ice), then its partial concentration is not given. For example,
=CT91ST
- thick
first-year ice with concentration of 9-10/10.
In addition to total
concentration and age categories, the characteristics of the ice cover of the
main zones include, if observed, the forms (code table 4) and additional
generalized characteristics (code table 5). If these data are given
after partial concentration of ice of a definite age category, they refer to
the ice of the indicated age within the boundaries of the main zone. If the
forms and additional characteristics are given after the symbol ":",
they refer to all ice in the zone. In particular, ice rafting is typical only
of nilas and young stages. even if ice of this age was
observed, some ice can have rafting and other ice not. Hence the ZR identifier
is given after the corresponding age category. The quantitative estimate if it
is determined, is expressed in tenths of the total
area of the zone. For example:
=nnnCT99SI50SG40ZR20SL10
- total
concentration is 10/10, thin first-year ice is 5/10, gray ice - 4/10, 2/10
being rafted ice, light nilas -1/10. The situation with determination of the
forms is quite different. The drifting ice cover of the seas presents, as a
rule, ice breccia of different age categories. Only the most
old ice has the form of the floes, all other ice presents ice-free water
zones, fractures and leads frozen at different time after the onset of ice
formation. Hence in terms of the methods it is more correct to indicate average
or prevailing size (forms) of the most old ice and at the end after the symbol
":" the size of the breccia floes restricted by cracks, leads and
fractures of the most young ice or ice-free water (if total concentration is
less than 10/10. For example,
=
nnnCT99SM20FMST50SK20SN10:FV
- total concentration is
10/10, multiyear ice 2/10 medium floes, thick first-year ice 5/10, medium
first-year ice 2/10, nilas 1/10, vast breccia floes of multiyear, thick and
medium first-year ice.
Concentration of hummocks
and ridges can be characterized either by a relative area occupied by hummocks
in hundredths or by a number of pressure ridges per nautical mile. For these
cases different identifiers (ZH and ZI) are envisaged. The
characteristics of the snow cover depth, stages of melting, pollution on the
ice, surface relief of multiyear ice are reported if observed, by the
identifier assigned to each characteristic and conventional units
according to the corresponding scales (code tables 12-15). Zones of
pressures and discontinuities in the ice cover are, as a rule, not related to
age boundaries and hence are coded as separate zones delineated on the basis of
these additional characteristics. The order of their description is presented
in Section 8.
The section INF ends like the other sections, by a
group 999999999, which is situated on a separate line.
7. CODING OF THE BOUNDARIES OF THE
MAIN ZONES
The section of the
boundaries of the main zones begins with the constant BOUND on a separate line. The position of
the boundaries of the zones is approximated by the segments of the straight
lines between the turning points. The order of forming the nine character
groups determining the position of some point at the chart in the geographical
coordinates is described in Section 4.
The number and position of
the turning points of the boundaries should be optimal for describing the
contours of the zones. The deviation of the observed, as a rule, curvilinear
boundary on the chart from the segment of a straight line between the two
turning points can serve as a criterion. Taking into account that the position
of the turning points is described with an accuracy of 1' by latitude and
longitude, this deviation should not, probably, exceed 3 km for operational
charts and 5 km at the exchange of archived data. This conditions
allows automated selection of the points describing the contours of the zones.
The closed boundaries begin
and end with one and the same point. The boundaries of the zones can be partly
or completely the shores, the boundary of data collection (ice chart) and
earlier coded boundaries of the other zones. The contour of each zone should be
closed from all sides without gaps. The joining points of the boundaries of
other zones except for the points adjoining the coastline,
should be repeated for describing each of these zones.
The coordinates of the
coastline points are stored in a separate permanent database. To avoid this
condition is possible by indicating the joining point not on the coastline, but
on the shore itself at the continuation of the first or the last segment of the
boundary.
Thus the boundaries of the
zones are described by lines - broken segments of the boundaries between the
joining points with other lines. The lines are separated by the symbol:
(division). The line can consist of only two joining points, but in the general
case the number of the points on the line is not limited. The lines include
nodes - the joining points of the boundaries of other zones and points - simple
turning points. Such a subdivision into lines, nodes and points allows, if
necessary, a rational editing or conversion to the calculation-analytical
charts of the letter-digital ice charts in the CONTOUR-2 format.
Separate lines contouring
some zone or other are, as a rule, described in different places of the section
BOUND. Hence closed contours of all zones are obtained only after the
entire section is displayed or plotted.
The presence of an
information point given in the INF section in each zone,
enables us not to form separate files of the closed contours of each zone when
data are gridded. This makes the conversion procedure much more
simple.
8. DESCRIPTION OF THE ZONES
DELINEATED BY ADDITIONAL CHARACTERISTICS
Zones delineated by the
additional generalized characteristics present separate layers of the ice
chart, each of them being identified using only one characteristic. Its
identifier (code table 5) follows directly the symbol =. For describing such
zones no other characteristics are presented.
In the practice of
compiling the ice charts such an approach is most frequently used for
describing the dynamic processes and their results (zones of pressures,
fractures, cracks and leads or zones of leads). As
mentioned, the boundaries of such zones in the general case are not connected
with the age categories and hence can be situated within large main zones or
cross the boundaries of the zones of different age categories.
The zones of pressure
(compacting) are coded by the ZC identifier followed by a two-character
code symbol which characterizes the degree of pressure (code table 11).
For example,
=ZC20
- zone
of considerable pressure (compacting).
According to the
Nomenclature, the strength of pressure (compacting) is described by three
gradations - slight, considerable and strong. However, observers often assess
it by intermediate values 1-2 and 2-3. The use of a two-digit group in the code
allows the initial estimate to be preserved.
Non-uniform ice drift
results in mutual shears, break-up of the solid ice cover and formation of
cracks and leads. The presence of such zones in the drifting ice is usually
related to the boundaries of the ice drift in different directions and is quite
interesting for selecting the motion route through the ice and studies of the
ice cover dynamics. Formation of cracks and leads in fast ice, their amount and
orientation characterize the onset and the extent of fast ice break-up and
should be by all means indicated on the ice charts.
The zones of fracturing
(cracks and leads) are coded by the ZF identifier followed by one or two
(according to the number of the observed systems of approximately parallel
cracks and leads) four-character groups LLAA where LL - mean
distance between the cracks and leads in km, AA - azimuth, relative to
meridian of the information point in tenths of degrees. For describing the zone
of leads after the ZL identifier one or two (according to the number of
the observed lead systems) six character groups LL..AA..TK..LL..AA..TK..
groups are recorded where the values LL and AA are similar to
the preceding ones, T - a distinguishing feature of the subsequent
indication of the width of the leads by code (code table 11), K -
code value of the width of the leads.
After each of these groups,
if possible, the identifier of the age category of ice formed at the surface of
the leads of this system, is written. For example,
=ZL
1512T3SG 2005T2SN /812015400/
- zone of two systems of
leads: in the first - mean distance between the leads is 15 km, the azimuth
relative to meridian is 154 120 , the width is 1.5-3 km, covered by gray ice;
in the second - mean distance between the leads is 20 km, azimuth - 50, mean
width is 0.5-1.5 km, nilas was formed on the surface.
Fractures usually represent
leads deformed as a result of shears. Due to non-linearity, each lead at shears
expands in some places and closes in other places and thus a chain of fractures
is formed, whereas a series of roughly parallel chains is formed of the system
of leads..
The zone of fractures is
described by the ZP identifier after which a six character group LLAAYY
is written where LL - mean distance between the chains of fractures
in km, AA - azimuth relative to meridian of the information point, YY
- mean distance between the fractures in the chains in hundred meters. Such
additional characteristics as concentration of hummocks and ridges, snow depth,
stages of melting are usually reported for describing the main zones delineated
by concentration or age. It is assumed that the boundaries of the zones of main
and additional characteristics coincide. However, sometimes it is necessary to
show the actual boundaries of the zones of increased concentration of hummocks
and ridges or vice versa level ice, zones of varying stages of melting or other
additional characteristics. In these cases after the symbol "="
the corresponding identifier (code table 5) and a quantitative estimate
of this characteristic are written. After describing the additional generalized
characteristic by which a zone was delineated, the coordinates of the information
point between the symbols / / are written and then on a new line the
coordinates of the turning points of the zone contour which are coded according
to the general rule.
The contours of additional
zones should be closed (the first and the last points are repeated) or can be
closed to the coastline, the boundary of data collection of the ice chart, the
boundary of the zone of a similar additional characteristic which has a
different numerical value. For example, the boundary of the zone of slight compacting
can be closed to the boundary of considerable or strong compacting. The
boundaries of the zones delineated by additional characteristics cannot be
closed to the boundaries of the main zones, additional zones delineated by
other characteristics or to linear targets.
9. A SECTION OF LINEAR OBJECTS
The linear objects whose identifiers are given in code table 6,
mainly describe ice-free water zones among ice and characterize the dynamic state
of the ice cover. Such objects as flaw, ridged ice and a crack do not require
information on the ice age category and width. However, for a complete
description of the leads and flaw and shore leads it is necessary to indicate
the ice age category at their surface and width (by two characters in hundred
meters). For example,
=LL03SG
- a
lead 300 m wide covered by grey ice.
When it is impossible to
determine the width of the lead accurately, in particular from satellite low
and medium resolution imagery as well as for coding of several leads, their
width is indicated according to code table 11. The ice edge, i.e. the
boundary between ice-free water and sea ice of any age category, is usually
described as a boundary between the zones whose description begins with the
identifiers CW and CT or CF. Hence the identifier LE
is used only for visual observations if observer can determine the geographical
position of the ice edge to the side of the route, but cannot distinguish any
characteristics of the ice behind it. After the characteristics of the linear
object the information point is not given, but from the new line the
coordinates of its turning points are presented which are coded according to
the general rule. If several linear objects with the same characteristics are
plotted on the chart, then this characteristic is coded only once after which
the turning points of each object of this type are reported on a new line. The
groups of coordinates of separate ice formations are separated by the symbol :. The description of the coordinates of the next
linear object after the symbol : can start on the same
line. For example,
=LLT3SW
721205430
721605445:771307012 770406930 763506820 .......
=LLT2SN
741307500
752007100 ..........
If there are no data on the
age categories or width or simultaneously on both characteristics, they are not
given.
10. A SECTION OF POINT OBJECTS
The point objects that
should be indicated on the ice charts (depending on their scale and purpose),
include icebergs, stamukhas, separate ice floes, as well as the ice thickness
measured at a point. For describing the point objects, on a separate line there
are given in succession the identifier of the object (code table 7), the age
identifier (for ice floes) and by a two-digit group the size by the largest
section in hundreds of meters. If the size of the object exceeds 10 km, the
geographical coordinates of the ends of the segment of the largest section are
reported instead of the size in the symbols / / without the separating symbol between
the groups of coordinates. For example,
=PL/821516435
822116511/
- a
drifting ice island whose size (about 14 km) and position are reported by the
coordinates of the ends of its large axis.
For iceberg coding after
the identifier PI or PT defining the main iceberg types, their
size can be indicated in hundred meters or according to code table 16.
After the identifier PV
(ice thickness measured at a point) a two-digit group indicates the measured
ice thickness in decimeters with rounding off up to whole values, i.e. with an
accuracy of 5 cm. After characterizing the object the geographical coordinates
of the information point defining its position (for objects less than 10 km in
diameter) are reported by one nine-digit group in the symbols / /.
In case of describing
several point objects with similar characteristics (for example, stamukhas or
icebergs, if their size is not given) the identifier is written only once and
the coordinates of the information points defining the position of the objects are
separated by the symbol :. For example:
/761414215:772514356
....../
11. A SECTION OF THE ICE DRIFT
The terms and notions
presented in table 8: ice fracturing, ice shearing, ice diverging and their
identifiers are used as a rule for characterizing the dynamic state of the ice
cover in the main zones or in local regions without indication of any numerical
values. Hence their application does not require special explanation. However,
automated processing of successive satellite or instrumental airborne surveys
allows us to obtain quite a detailed field of the drift vectors. In order to
avoid too much information on the general ice situation chart and facilitate
its reading, all the determined drift vectors are usually depicted only at
special drift charts or at the charts of the dynamic state of the ice cover.
However, information about separate drift vectors allows an objective analysis
of the changes in the distribution and characteristics of the ice cover to be
performed. Hence information on the drift of separate ice floes, icebergs,
automated buoys should be included to the digital ice chart.
Coding of the drift
parameters is performed in the form of separate records grouped by observation
means and periods. Each record starts after the symbol "="
with the identifier of the methods and means of observation followed by the
observation time:
=RRr'n:MMDDtt..-MMDDtt..,
where PP - observation method (code
table 1), r.. - a meaningful digit of the route-mean-square (rms)
error of determining the coordinates using the indicated observation means and
method in a specific region in meters, n - power indicator 10, MMDD
- date (month, date), tt - hours (UTC time). The indices 1 and 2
correspond to the start and end of the observation time interval of observations
for the drifting formations of this group.
Methods and means of
observations were enumerated in the header-record of the ice chart. However
there the resolution was indicated and in the ice drift section which begins
with the constant DRIFT, the root-mean-square error of coordinate determination which also
depends on the accuracy of navigation, processing method, the presence of
reference points, etc. being always worse than the resolution, i.e. r'>r.
Only for buoys and automated ice stations in both cases the accuracy of
positioning and r'=r are given. Then on a new line using ten-digit
groups the geographical coordinates of the start and end of each vector of this
group, (i.e. for one period and by one means) are recorded. First five digits
denote latitude with an accuracy up to 0.1', the six
to ten digits - longitude with an accuracy (by rounding off) up to 1'. Data on
each vector occupying two groups are separated by the symbol
:. On one line 6 ten-digit groups should be situated which corresponds
to three drift vectors. For example,
DRIFT
=P143:022614-030215
8116415618
8123715553: ...... ........
- the drift based on
satellite observation data in the IR range, the rms error of coordinate
determination plus-minus 4 km, first determination of coordinates is on
February 26, at 14 UTC, second - on March 2 at 15 UTC, the coordinates 81°16.4'
156°18' - 81°23.7' 155°53'.
12. CODING OF DATA OF EN-ROUTE
OBSERVATIONS
Visual airborne
observations allow almost all ice cover characteristics to be estimated. If
aircraft or helicopter was equipped by a radar ice thickness meter and laser
profiler, then it is also possible to obtain objective data on the thickness of
ice varying age categories per unit route which can be used for specifying model
calculations and the models themselves. Therefore, if at the time of compiling
a composite chart there are data of en-route observations they are included to
a letter-digital composite ice chart in a separate section. The ice thickness
and surface relief are directly observed under aircraft. The width of the strip
of visual observations for determining other main characteristics does not
exceed several kilometers and also presents a line at the chart scale. Hence
data are coded as route segments which are assigned some set or other of the
main and additional characteristics. The section begins with the constant ROUTE on a separate line. Then the
geographical coordinates of the point of the start of observations are reported
(crossing the coastline, boundaries of information collection of the ice chart,
take off from board the icebreaker or runway at the drifting ice). For this
purpose the identifier CU or CL are used. It is followed by the
coordinates of the start of observations within the chart under preparation.
Then the ice characteristics on the route segments are coded in succession
according to the rules presented in Section 6 using same code tables and the
order of describing the numerical values of variables, separating and service
symbols. The route segments are not numbered and right after the symbol = the
identifier CP is written.
All additional generalized
characteristics at each route segment are described with the main ones and not
in a separate block. Therefore at the change in any main or additional
characteristic or numerical values of some characteristic a separate route
segment is delineated.
After describing all ice
characteristics in the symbols / / the geographical coordinates of the end of
the route segment with these characteristics are indicated by one nine-digit.
This point is simultaneously the start of the next route segment. Thus each
route segment with the assigned set of characteristics is restricted by the
coordinates of the end of earlier coded segment written in the symbols / / on
the previous line and the coordinates of the end of the given segment.
If ice characteristics did
not change at the turning points of the route (when turning to the next
rectilinear segment), first the coordinates of the turning point and then after
a "gap" the coordinates of the end of the route segment are reported
in the symbols / /.
The linear objects observed
along the route are coded in a separate block which is reported on a separate
line by the constant LINE OF ROUTE. Each linear object is also written on a
separate line. For coding a lead after the symbol = the identifier LL is
written. It is followed by its azimuth relative to meridian of the crossing
point of the lead by the route in tens of degrees, the width in hundred meters
and age category of the ice formed at its surface. For flaws and hummocks,
drift divides and boundaries only azimuth is recorded.
After characteristics of
the linear object the geographical coordinates of its crossing point by the ice
reconnaissance route are indicated in the symbols / /. If the linear object was
situated aside from the segment and parallel to it and therefore was not
crossed by the route, the coordinates of the object during its observation
period are indicated in the symbols / / by two or three groups. In these cases
the azimuth and the age category of the ice formed at the surface of the lead
are not determined and the width is indicated by code (code table 11).
For example:
LINE
OF ROUTE
=LL1604SG
/723415042/
=LLT2
/724315124 732515146/
- a lead whose azimuth
relative to meridian 150° is equal to 160°, the width to 400 m covered by grey
ice, was crossed by the ice reconnaissance route at the point of 72°34' and
150°42'.
Point objects are described
in the block POINT OF ROUTE fully preserving the methods presented in
Section 10. In the symbols / / there are indicated the coordinates of the
objects which depending on their position can be both on the route and aside
from it. The ice drift even at successive en-route surveys in one and the same
region is not observed. Thus in the section ROUTE the crossings of the
main zones are described including all additional characteristics, linear and
point objects.
In the section TEXT, if
necessary, information is presented in plain language which is considered
necessary for a correct understanding and use of the coded ice chart. This
information includes observation conditions, failures in operation of the
equipment on board, reception distortions, non-standard processing methods, the
use of previous observation data or calculations, etc.
14. DISSEMINATION OF OPERATIONAL ICE
INFORMATION, EXCHANGE OF ARCHIVED DATA
Operational ice information
is reported to users via communication channels in the form of separate
letter-digital charts with the addition of the address block which is formed
according to the national or international communication rules and is not
considered here.
When a cable-chart is
transmitted via a communication line, for users not having computers with
corresponding software and code tables, the letter symbols (identifiers) of ice
characteristics can automatically be replaced by the terms of the Nomenclature
in the user's language. For example: instead of CF - fast ice, SM multiyear,
etc.
It is planned that the
exchange of archived data between the Ice Services and Data Banks will be by
sending the magnetic tapes with the recorded ice charts. It is desirable that
every tape included a set of uniform ice charts from one Ice Service covering
approximately one and the same region.
Each tape should contain
the header-record and files of the ice charts.
The header-record of the
tape is recorded in the following format:
CONTOUR-2:
INF
AAFF:NNN
MMLLL1
MMLLL2
YYMMDD1
YYMMDD2
where: AA -
originating country, FF - originating Service, NNN - total number
of digitized charts on a tape, MMLLL with indices 1 and 2 - minimum and
maximum latitude and longitude of the observation region in degrees, YYMMDD
with indices 1 and 2 - year (two last digits), month and date of the first and
last chart by time recorded on the tape.
After coding the service
information, if necessary, any other information pertinent to the entire tape
is included as a free text. In particular, new additional terms and their
definition, deviations from the agreed coding procedures and other messages
necessary for correct data use are reported.
For information coding the
code tables 1-8 are used. They contain two-letter identifiers which provide non-ambiguous
determination of each ice variable (characteristic) in the zones or ice objects
and tables 9-17 presenting scales for a quantitative or qualitative assessment
of these characteristics.
For a more complete and
objective description of the ice cover, code tables 1-8 include some terms
which are absent in the WMO Sea-Ice Nomenclature (residual first-year ice,
rough ice, drift divide, etc.). These additional terms which are used in the
The format CONTOUR-2
envisages, if possible, indication of the true numerical values of the
variables (total and partial concentration in tenths and hundredths, size in
hundred meters, thickness in decimeters, etc.). The recommendations of the
format and the Nomenclature do not always coincide. In particular, the WMO
Nomenclature envisages indication of the area of hummocks in tenths. However,
this is not statistically justified, as the maximum relative area of hummocks
does not, as a rule, exceed 20-25%. Hence CONTOUR-2 proposes to indicate it in
hundredths.
The scales in code tables
9-17 are mainly used for a qualitative assessment (ice compacting, surface
relief of multiyear ice) or if the quantitative assessment is not given in
accurate values but within some limits (mean widths of leads in the zone,
number of icebergs, etc.).
The scale of the stage of
melting has significant shortcomings (code table 15). It does not characterize
on the whole the stage of melting of the ice cover, non-uniform by the age
category, but requires to indicate the stage of
melting of each age gradation. This scale, like some other scales, is mainly to
be used for visual observations which currently have a very limited application.
However, to formulate the objective indications of different stages of melting
based on remote sensing data in varying ranges, it is necessary to carry out
joint international studies to specify this and some other scales. Hence here
the scale given in WMO Nomenclature is presented.
Code table
1.
Observation methods and means
|
Observation methods and means |
Identifier |
|
Satellite observations in the
visible range |
PV |
|
Satellite observations in the IR
range |
PI |
|
Satellite radar observations |
PR |
|
Satellite passive microwave
observations |
PS |
|
Visual observations from aircraft |
AV |
|
Survey in the IR range from
aircraft |
AI |
|
Radar survey from aircraft |
AR |
|
Visual shipborne and coastal
observations |
|
|
Observations by means of coastal
radars |
LR |
|
Data from buoys and automated ice
stations |
LA |
|
Interpolation data |
DI |
|
Averaged gridded data |
DA |
|
Actual data at the grid point |
DP |
Code table
2.
Ice distribution
|
No. from the WMO Sea-Ice
Nomenclature |
Characteristic |
Identifier |
|
3.1. |
Fast ice |
CF |
|
4.2. |
Total concentration |
CT |
|
- |
Concentration in strips and
patches |
CS |
|
4.2.7. |
Bergy water |
CI |
|
4.2.8. |
Ice free water |
CW |
|
4.3.2.1. |
Giant ice floe whose contour is
then described |
CP |
|
- |
Region where observations were not
performed by meteorological or other reasons. |
CU |
Note:
- CS is only used as an additional
characteristic after CT.
- After CW and CU there can be no characteristics.
- After CI concentration and number of icebergs can
be reported.
Code table
3.
Stage of development
|
No. from the WMO Sea-Ice
Nomenclature |
Characteristic |
Identifier |
|
2.1. |
New ice |
SA |
|
2.1.2. |
Grease ice |
SQ |
|
2.1.3 |
Slush |
SC |
|
2.2. |
Nilas |
SN |
|
2.2.1. |
Dark nilas |
SD |
|
2.2.2. |
Light nilas |
SL |
|
2.2.3. |
Ice rind |
SR |
|
2.3 |
Pancake ice |
SP |
|
2.4. |
Young ice |
SY |
|
2.4.1. |
Grey ice |
SG |
|
2.4.2 |
Grey-white ice |
SW |
|
2.5. |
First-year ice |
SF |
|
2.5.1. |
Thin first-year ice |
SI |
|
2.5.1.1 |
Thin first-year ice/first
stage |
SJ |
|
2.5.1.2. |
Thin first-year ice/second
stage |
SE |
|
2.5.2. |
Medium first-year ice |
SK |
|
2.5.3 |
Thick first-year ice |
ST |
|
2.6. |
Old ice |
SO |
|
2.6.0 |
Remaining first-year ice |
SH |
|
2.6.1 |
Second-year ice |
SS |
|
2.6.2 |
Multiyear ice |
SM |
|
10.4.2 |
Ice of land origin |
SB |
|
|
Ice more old than earlier
indicated |
SX |
|
|
Thickness of uniform ice in the
zone |
SV |
|
|
Ice of undetermined age |
SU |
Note:
- It is permitted to indicate two age stages
which are not even included into one main age gradation, and then their
total partial concentration. For example: SWSIff.
- SX is used only after the specific age
stage.
Code Table 4 Forms of floating ice
|
No. from the WMO Sea-Ice
Nomenclature No. from the WMO Sea-Ice Nomenclature |
Characteristic |
Identifier |
|
4.3.2.1. |
Giant ice floe |
FG |
|
4.3.2.2. |
Vast ice floe |
FV |
|
4.3.2.3. |
Big ice floe |
FB |
|
4.3.2.4. |
Medium floe Small floe and ice cake |
FM FR |
|
4.3.2.5. |
Small floe |
FS |
|
4.3.3. |
Ice cake |
FC |
|
4.3.3.1. |
Small ice cake |
FT |
|
4.3.5. |
Ice breccia floes |
FW |
|
4.3.6. |
Brash ice |
FP |
Code Table
5.
Additional generalized characteristics
|
No. from the WMO Sea-Ice
Nomenclature |
Characteristic |
Identifier |
|
5.2. |
Zone of compacting
(pressures) |
ZG |
|
6.1. |
Zone of fracturing (cracks and
leads) |
ZF |
|
7.2. |
Zone of fractures |
ZP |
|
7.3. |
Zone of leads |
ZL |
|
8.2.1. |
Rafted ice |
ZR |
|
8.2.1.2. |
Rough ice |
ZE |
|
8.2.3.1. |
Hummocked ice (with areal coverage). Frequency in number of ridges per
1 nautical mile |
ZH ZT |
|
8.2.3.2. |
Concentration of hillocks of
multiyear ice |
ZX |
|
8.6. |
Snow-covered ice |
ZS |
|
8.7 |
Polluted ice |
ZG |
|
9. |
Stage of melting |
ZM |
|
10.4.2. |
Number of bergs |
ZI |
|
|
Floe size distribution |
ZD |
Note: The term “Floe size distribution” is
mainly used for coding the archived ice charts of the
Code table
6.
Linear objects of the ice cover
|
No. from the WMO Sea-Ice
Nomenclature |
Term |
Identifier |
|
4.4.8. |
Ice edge |
LE |
|
5.4.1. |
Drift divide |
LR |
|
7.1.1. |
Crack |
LC |
|
7.1.1.2. |
Flaw |
LP |
|
7.3. |
Lead |
LL |
|
7.3.1. |
Flaw and shore leads |
LS |
|
8.2.2.6. |
Ridged ice |
LT |
Code Table
7.
Point objects of the ice cover
|
No. from the WMO Sea-Ice
Nomenclature |
Term |
Identifier |
|
3.4.2. |
Stamukha |
PG |
|
4.3.2. |
Separate ice floe (size can be
indicated, but the contour is not described) |
PF |
|
10.4.2. |
Iceberg |
PI |
|
10.4.2.2. |
Tabular berg |
PT |
|
10.4.3. |
Drifting ice island Ice thickness measured at a
point |
PL PV |
Code Table
8.
Dynamics and deformations of the ice cover
|
No. from the WMO Sea-Ice
Nomenclature |
Process |
Identifier |
|
5.1. |
Ice diverging |
DE |
|
5.3. |
Ice shearing |
DS |
|
5.4. |
Ice drift |
DP |
|
6.1. |
Ice fracturing |
DF |
Code Table
9.
Total and partial concentration
|
Concentration |
Code symbol |
Concentration |
Code symbol |
|
1/100 |
01 |
1/10-3/10 |
13 |
|
2/100 |
02 |
4/10-6/10 |
46 |
|
.. |
... |
7/10-8/10 |
78 |
|
9/100 |
09 |
9/10-10/10 |
91 |
|
<1/10 |
00 |
... |
... |
|
1/10 |
10 |
91.3/100 |
92 |
|
2/10 |
20 |
96.8/100 |
96 |
|
... |
... |
... |
... |
|
9/10 |
90 |
97.2/100 |
98 |
|
10/10 |
99 |
99.4/100 |
99 |
Note:
- Ice-free water is coded by the identifier
CW.
- At instrumental observations it is
possible:
- a) within the interval 1/100 - 9/100 - to
report concentration with an accuracy up to 1/100;
- b) within the
interval 9/10-10/10 - to report concentration with rounding off up to
even values of hundredths.
Code Table
10.
Ice compacting (pressures)
|
Characteristic |
Code symbol |
|
Ice compacting, intensity is not
reported |
00 |
|
Slight compacting |
10 12 |
|
Considerable compacting |
20 23 |
|
Strong compacting |
30 |
Note: Intensity of compacting is
reported after the identifier ZC. It is possible to indicate
intermediate values of intensity of 1-2 and 2-3 units (coded by 12 and 23).
|
Width of leads (km) |
Code symbol |
|
0.05 - 0.3 |
TO |
|
0.3 - 0.5 |
T1 |
|
0.5 - 1.5 |
T2 |
|
1.5 - 3 |
T3 |
|
3 - 5 |
T4 |
|
>5 |
T5 |
Note:
Code designation of the width of leads is reported after the identifiers ZL
or LL. The observed width of a specific lead can be indicated in
hundreds of meters by a two-letter number without the identifying letter T.
|
Characteristic |
Code symbol |
|
No snow |
TO |
|
Up to 5 cm |
T1 |
|
Up to 10 cm |
T2 |
|
Up to 20 cm |
T3 |
|
Up to 30 cm |
T4 |
|
Up to 50 cm |
T5 |
|
Up to 75 cm |
T6 |
|
Up to 100 cm |
T8 |
Note: The code symbol of the snow depth is
reported after the identifier ZS. It can also be reported in cm by a two
digit number without the identifying letter T. If snow depth is unknown, the
identifier ZS and its numerical value are omitted.
Code Table
13.
Surface relief of multiyear ice
|
Characteristic |
Code symbol |
|
Smoothed multiyear ice |
T1 |
|
Moderately hillocky ice |
T2 |
|
Strongly hillocky ice |
T3 |
Note: The characteristic of the multiyear
ice surface is reported after the identifier ZX.
Code Table
14.
Relative area of polluted ice
|
Characteristic |
Code symbol |
|
Clean ice, traces of pollution |
T0 |
|
Slight pollution. The area of
polluted ice is less than 1/3 of the entire sighted ice area. |
T1 |
|
Average pollution. From 1/3 to 2/3
of the ice area polluted. |
T2 |
|
All ice polluted. More than 2/3 of
the ice area polluted. |
T3 |
Code Table
15.
Stage of melting
|
Characteristic |
Code symbol |
|
No melt |
T0 |
|
Few puddles |
T1 |
|
Many puddles |
T2 |
|
Flooded ice |
T3 |
|
Few thawholes |
T4 |
|
Many thaw holes |
T5 |
|
Dried ice |
T6 |
|
Rotten ice |
T7 |
|
Few frozen puddles |
T8 |
|
All puddles frozen |
T9 |
Code Table
16.
Specification of icebergs (as established by the International Ice Patrol
Service)
|
Size |
Height (m) |
Length (m) |
Code |
|
Growler & bergy bit |
up to 5 |
less than 5 |
TO |
|
Iceberg, small |
6-15 |
16-60 |
T1 |
|
Iceberg, medium |
16-45 |
61-122 |
T2 |
|
Iceberg, large |
46-75 |
123-213 |
T3 |
|
Iceberg, very large |
over 75 |
more than 213 |
T4 |
Note: Sizes refer to the above-water
portion only. If the height and length of a berg fall into different size
classification, use the larger size. Dimensions of a tabular berg or ice island
may be indicated by a two-digit number in hundred meters. If they exceed 10 km
- by indication of the coordinates of the ends of the largest section in
symbols / / or by contour description.
Code Table
17.
Relative number of icebergs
|
Number of icebergs in the radius
of |
Distance between icebergs |
Code symbol |
||
|
20 km |
30 km |
miles |
km |
|
|
- |
- |
- |
- |
T0 |
|
not more than 1 |
not more than 1 |
more than 45 |
more than 80 |
T1 |
|
1 - 2 |
1 - 7 |
15 - 45 |
28 - 80 |
T2 |
|
3 - 4 |
8 - 15 |
10 - 15 |
18 - 28 |
T3 |
|
5 - 8 |
18 - 34 |
7 - 10 |
13 - 18 |
T4 |
|
9 - 16 |
35 - 65 |
5 - 7 |
9 - 13 |
T5 |
|
17 - 44 |
more than 65 |
3 - 5 |
6 - 9 |
T6 |
|
more than 44 |
|
1 - 3 |
2 - 6 |
T7 |
|
|
|
0,5 - 1 |
1 - 2 |
T8 |
|
|
|
less than 0.5 |
less than 1 |
T9 |
TERMS ABSENT IN THE WMO SEA-ICE NOMENCLATURE
AND INCLUDED TO CODE TABLES
Multiyear experience of
using “WMO Sea-Ice Nomenclature” and scales it contains for support of
practical activities at seas indicates the need to supplement the Nomenclature
by new terms and specify the scales. Such proposals were considered at the Vth
session of the WMO CMM WG on Sea Ice (Geneva, August 1988). However, no opinion
of the WAG was formulated and no necessary implementation steps were undertaken
up to present. As mentioned in the document presented to the WG, the
Nomenclature along with a too detailed description of separate ice formations
(for example different types of ridges) does not contain definitions of a
number of generalized ice cover characteristics, processes and ice formation
(age categories, surface topography, ice drift, drift divide, etc.). Some terms
describe the process not quite accurately. Thus the term “concentration” is
used, as a rule, for estimating pressures in conventional units and not for
estimating the decrease in total concentration.
However, the format
CONTOUR-2 does not aim at reviewing the WMO Sea-Ice Nomenclature or its
complete correction. This Annex contains only the terms and their description which are included to the code tables and are
necessary for correct understanding of coded information. These terms are
assigned the numbers of the Nomenclature where they can be included to without
breaking its structure.
- 2.6.0. Remaining first-year ice: First-year ice
which has not melted in summer and is in the new cycle of freezing. Its
thickness, depending on the region where it was in summer, from 60 to
160-180 cm. After the 1st of January (in the Southern Hemisphere after the
1st of July) this ice is called second-year ice.
- 4.3.0. Floe size distribution: The extent of ice cover fracturing. Determined from a mean
distance between the cracks and leads or from a relative number of the ice
floes in the zone.
- 5.2.1. Ice under pressure: Further stage of ice
compacting after reaching a concentration of 9-10/10. At ice pressure its
rafting or hummocking usually occurs.
- 5.2.2. Zone of ice under pressure: Zone where
ice under pressure is observed.
- 5.4. Ice drift: Progressive ice floe motion
as a result of wind and current effect.
- 5.4.1. Drift divide: A boundary between ice
massifs or ice zones drifting in different directions or with a different
speed. An indication of the drift divide is predominant small floe and ice
cake, flaws, ridged ice, leads and zones of diverging.
- 8.2.1.2. Rough (or irregular non-level) ice:
First-year ice subjected to fracturing and hummocking at the young ice
stage, formed as a result of pancake ice freezing or freezing of fragments
of fresh hummocks collapsed to fractures after the end of compacting and
the beginning of ice diverging. The non-homogeneities of this type cover
considerable areas where snow accumulation significantly increases and
heat conductivity and tangential stress coefficient significantly change.
As a result of further freezing, at the end of winter the irregularities
at the bottom surface of rough ice are usually completely smoothed and the
ice thickness becomes approximately equal to the ice thickness of the same
age category of quiet growth. For the period of summer melting all minor
irregularities on the surface of the ice floes become smoothed. Hence this
topography type is characteristic only of first-year ice. Ice roughness is
estimated in tenths as a ratio of the rough ice area to the total area of
the zones where assessment is made.
- 8.2.3.2. Concentration of the hillocky multiyear
ice: Characteristic of multiyear ice relief at whose surface as a result
of smoothing of pressure ridges and non-uniform melting in the preceding
years, the hillocks are formed.
- 8.7. Polluted ice: Ice which has at its
surface or in its stratum varying mineral or organic mixtures which make
it look polluted.
EXAMPLE OF CODING A COMPOSITE ICE CHART
CONTOUR-2
OBSERVATION:
0156
784606600
811005400 820009723 783609328
950317
950322
MAP
PV33
METEOR 6718 950317 /803008915/
PI13
NOAA 0841 950322 /804507415/
PR21
ERS 1416 950321 /802206743/
LIMIT
783609335
791908253 790007500 792707000 792106829 791706736 793506650
794406632
800006238 802206200 811806057 812706452 813306854 813608132
813508225
815709738 785409355 783609335 : 813508225 801408305 790007500 :
794406632
804506338 810606812 793507130 792707000
ROUTE
AV10
AN26 0027 950318
795309150
804608132 791007854
999999999
INF
=001CFST
/ 801209118 : 810706328 /
=002CT99SN
/ 804009037 : 804807845 : 792807548 : 791707900 : 791607748 /
=003CT99SN
/ 803008800 /
=004CT99SO70FMST20SG10
/ 811508632 /
=005ÑT99ST60SK30SG10
/ 794708350 /
=006CT91SO34ST40SG20
/ 800407303 /
=007CT99SO60SF40
/801206400 /
=008CT99SO80ST20
/ 804406730 /
=009CT99SO50ST30SK20
/ 800406647 /
=010CT99SO20ST50SK30
/ 794006838 - 792006550 /
=011CT99ST50SK40SG10
/ 793707025 - 790006855 /
999999999
BOUND
811209515
810609342 810509240 811009118 810009035 805309130 804009135
800509016
794508957 792109037 790709138 790009228 785409355:810809015
810608850
810308827 805708830 804708925 794508838 792408940 791509023
790709138:805708830
803508705 802208638 801108700 795408656 794508740
792708822
792408940:802208638 801508500 802308257 801608300 801907930
802507428
803207131 803807028 803706928 810506820 805206514:812706452
812006525
811506515 804206426 803706400 802206200:801907930 801307841
800907650
795007535 793907336 794507134 794507110 795507052 802906934
803706920:802906934
802506912 802706600 804606441:795507052 800006840
793506650
794406632 803706400:794507110 794207115 793806949 792106829
:804808012
804307915 804207745 804807750 805507912 804808012:792707738
792007545
792507500 793707605 792707738:791608000 791407845 791807835
792107945
791608000
999999999
ZONE
=ZL
2004T3SN 1512T2SG /812207500/
813608132
811807828 810507235 811706933 813306854
999999999
LINE
=LLT4SN
814208447
812808316 812508322 812008230:811508235 810207902 804207555:
805507410
804007244 803507256 801207100 795006916 793706730
=LLT3SG
812206645
811406815 804707118:805507232 803907347 803407443 801507608
801207634
795707750:795407142 794107316 792207446
=LL04SL
802106947
793306650
=LR
811209630
814808742
999999999
POINT
=PIT2
/803706534/
=PT05
/800606830/
=PG80
/791807953/
DRIFT
=LA52:031114-031715
8139509457
8144309316
=PV63:031110-031715
8119608923
8119808817:8052409426 8050009317:7935408631 7932508556
PI33:031214-032211
8056707634
8050407523:7953207822 7946107715:7922807324 7918307239
ROUTE
=CL
/795309115/
=CFST
/800409008/
=CT90SL50SD40ZR10
/801008847/
=CT99SW30SG50ZR20SL20
/802308648/
=CT99SM40ST30SV16SISW30
/803408431/
=CT99SM80ST20SV18
/804608132 801508046/
=CT99ST60SV15SK40SV09:ZH05
/792107918/
=CT90SN
/791507900/
=CT99ST60SV15SK40SV09:ZH05
/790007838/
LINE
OF ROUTE
=LL0602SW
/803008512/
=LL1405SL
/793907936/
TEXT
In
the regions of individual charts PV and PI the stages of development
and boundaries of the main zones are plotted from data of preceding
observations and drift. The area of pressure ridges is in hundredths.
END
Example of a composite ice chart.
INFORMATION PROPERTIES OF REMOTE SENSING MEANS
The format CONTOUR-2
provides a possibility to determine time, methods and means for information
acquisition for each part of the composite chart or for the whole individual
chart. In order to estimate completeness, reliability and accuracy of the
information of the ice chart on distribution and characteristics of the ice
cover it is necessary to know information properties of the remote sensing
means used. These properties are known to personnel of the
Determination of the
parameters characterizing the state of the ice cover by remote sensing means
and accuracy depend on the range and the region of the spectrum of
electromagnetic waves, sensitivity and resolution. For addressing the
operational goals, instrumental observations in the visible and IR ranges are
made from satellites and in the visible range also by means of visual ice
observations from aircraft. Surveys by active microwave (SAR, SLAR) and passive
microwave instruments (microwave radiometers) are performed both from
satellites and aircraft. However, in this case the carrier type mainly governs
the tactical possibilities of the survey, rather than the information
properties.
1. Satellite
observations in the visible range
At present for ice
observations there are used multichannel scanning devices in the visible range
(380-760 nm) of high (0.2-1.0 km) and low (1.5-3 km) resolution. From these
images one can determine the position of the ice edge of more than 3/10 in
concentration, fast ice and its boundaries, flaw polynyas, total concentration
with an accuracy in the winter-spring season of 1.5/10 (low resolution images)
and 1/10 (medium resolution images). In summer during intense melting the
accuracy of determining this characteristic considerably decreases.
Approximate determination
of the ice age categories is possible only in the large zones up to the stage
of grey-white ice. Older ice is, as a rule, covered by snow and its albedo is
not already related to thickness. Some stages of melting can also be determined
("flooded ice", "dried ice"). The drift data can provide
indirect estimates about ice compacting or diverging for the period between
observations.
The leads are distinguished
if their width exceeds 1/3-1/2 resolution elements, it is possible to determine
it at a width of the leads more than 2-3 resolution elements.
Satellite images clearly
manifest the effect of integrating which allows us to identify the objects and
zones which present a number of ice formations, each of them being much less
than the image resolution area. Contrast targets (ice floes
at the background of open water or vice versa fractures in solid ice)
with the size by the largest section less than half the resolution element are
not depicted. However, several closely situated targets enhance or reduce the
total brightness of the corresponding resolution elements proportionally to
their area. This typical feature is used for determining total concentration
and only due to this effect the drift divides are detected.
A comparison of the
enumerated possibilities with the list of the navigation characteristics of the
ice cover shows that although by using the scanning visual range radiometers of
low and medium resolution many important characteristics are determined (total
distribution, systems of large leads, drift divides, ice drift), the total
amount of data is still insufficient and incomplete. Ice age categories,
rafting, concentration of hummocks and ridges, the character of the snow cover
cannot be determined. Only the largest leads and only some stages of melting
are observed.
However, the main
shortcoming of this information is its dependence on light and meteorological
conditions (presence of cloudiness). The survey can be made only at the height
of the Sun more than 5 degrees above the horizon. Hence observations in the
As to cloudiness it is
found that satellite ice observations in the visible range are possible not
only in the complete absence of clouds over the observation region, but at
sufficiently dense but transparent cloudiness. Probably, this is influenced by
the known effect of the "water sky" and "ice blink". As a
result, the cloud cover over the ice floes is additionally illuminated due to
diffused reflected light and over water area its illumination is much lower.
Hence sometimes at continuous clouds (although the accuracy and reliability of
determining concentration and the boundaries of zones considerably decreases or
even impossible) it is still possible to distinguish flaw polynyas and large
leads and even contours of giant floes among ice of less than 9/10 in
concentration. Only in the event of thick stratified clouds the details of the
ice situation are completely non-discernible on images.
Experience has shown that
in the
2. Satellite
observations in the IR range
For satellite ice
observations in the IR range the scanning radiometers in the complexes MSU-S
and MSU-M operating in the region 10.5 - 12 um which corresponds to the
atmospheric transparency window, are used. Observations are possible only at
below freezing air temperatures, i.e. in the
Whereas in summer ice
concentration is the main navigation characteristic, in winter, when ice
concentration is equal everywhere to 10/10, age category (especially the amount
of young ice) becomes the main characteristic. Also important are the position
and characteristics of leads and fractures, flaw polynyas, drift divides,
concentration of hummocks and ridges, snow cover, dynamic state (drift,
compacting and diverging).
As a result of interpretation
and geolocation of IR imagery in the regions open from clouds, the following
can be determined:
- the position of the ice edge older
(depending on air temperature) than grey and grey-white ice with
concentration more than 3/10,
- fast ice and its boundaries,
- boundaries of uniform ice zones with 5-6
gradations in the thickness range from 0 to 100-120 cm, but without the
accurate determination of absolute thickness values,
- in dynamic regions such as the
Greenland and the
- the possibility for detecting the
leads and determining their width at the air temperatures of -30 to -50 C
is approximately similar as from the visible range images. At higher temperatures
the minimum width of the detected leads increases and the accuracy
decreases,
- ice drift from motion of the giant
floes, large fractures, characteristic points of leads is determined with
an accuracy of 5-6 km using low resolution images and 3-4 km - medium
resolution images.
The drift
divides and the remaining navigation characteristics cannot be determined from
IR imagery.
3. Ice
observations in the microwave band.
3.1. Use of passive
microwave instruments
The scanning microwave
multichannel radiometers which record their own underlying surface radiation in
separate regions of the range 0.1-40 cm, allow one (as a result of combined
processing of their signals) to determine the position of the ice edge at the
background of both calm and rough sea surface with an accuracy of 20 km,
delineate zones of prevailing young, first-year and old ice and determine the
position of their boundaries with an accuracy of 40-50 km and total
concentration with an accuracy of 2-3/10.
Due to low resolution (at
present at the surveys at satellite altitudes not better than 10 km for a very
high frequency channel) no ice formations can be detected and distinguished on
microwave radiometer images.
On the whole, this
information is more of climatic and not of an operational character for
shipping support. However, in combination with other satellite remote sensing
means, it allows supplementing their information by data on multiyear ice
boundary on the charts based on visible and IR imagery, and data on the ice
edge position which is often not discernible at the background of rough sea.
As additional information
which is used for ice forecasting, sea surface temperature and wind speed in
the surface air layer can be determined from data of microwave radiometry.
3.2. Radar sounding of
sea ice.
In addition to passive
microwave instruments (scanning and trace microwave radiometers), active
microwave instruments including synthesized aperture radar (SAR) and
side-looking airborne radars with real aperture (SLAR) are widespread for
satellite and airborne ice observations.
SAR surveys
("Almaz", ERS, RADARSAT) are performed with a very high (15-20 m) and
high (20-100 m) resolution and SLAR ("Okean") with a low (1.5-3 km)
resolution. Both SAR and SLAR surveys from aircraft are performed with very
high and high resolutions.
Based on amplitudes of the
signals or optical densities of radar images with a wavelength of 0.8-5 cm, it
is possible to determine ice age stages by main gradations (young, first-year,
old) and their partial concentrations. With the increase in the wavelength up
to 10-30 cm the contrast between first-year and old ice decreases and ice age
determination becomes difficult. In summer the amplitudes of the signals from
first-year and multiyear ice in all microwave range regions become equal and
ice age determination is impossible without using the texture and structural
indications.
From radar imagery the ice
edge position, fast ice boundaries, concentration and boundaries of the zones
of varying concentration can be determined. Ice of land origin (glaciers and
icebergs) and river ice, drift divides and flaws are distinguished quite well.
During surveys with a high
spatial resolution in zones of young ice, rafted ice can be observed and its
relative area can be determined and at the background of level first-year ice -
separate ridges. However, in zones of rough ice which has a very high
backscattering coefficient during the entire winter and spring seasons,
pressure ridges are not distinguished and the number of ridges or their
relative area is impossible to determine.
Leads and fractures if
their width exceeds 1/2 resolution elements, are depicted at the background of
first-year ice only during the period of grey and grey-white ice formation at
its surface and in multiyear ice zones - during the entire period of existence
of leads, even after medium or thick first-year ice is formed at its surface.
Since radar images do not
depend on illumination and weather conditions and high resolution, they are
most effectively used for regular ice drift determination, change in the
position of the delineated zones, their configuration and areas.
Thus based on radar images,
especially with high and low resolutions, most navigation parameters of the ice
cover can be determined. The limitations of this method are that age gradations
of first-year and old ice are not distinguished (it is impossible to subdivide
it into thin, medium, thick remaining, second-year and multiyear). Also, snow
cover, presence of pollution on ice, the process of ice compacting are not
observed. In spite of the existing preconditions (change of the character of
radar images in summertime) the interpretation indications of the stages of
melting are not yet formulated.
In spite of these
restrictions, complete independence on weather conditions and illumination, a
sufficient contrast between ice of different age categories and different
surface structure and high resolution allow us already now to consider SAR and
SLAR the main means of satellite and airborne ice observations.
4.
Visual observations from aircraft
Visual ice observations are
carried out from light motor aircraft and helicopters of varying types from a
height of 100-600 m. At flights at these altitudes the human eye ground
resolution can be assumed to be equal to 0.1 m.
Such a high resolution
allows an observer using such parameters as surface relief, snow cover state,
type of rafting and hummocked formations, ice thickness in fractured ice, size
and form of puddles, colour shades of the surface of ice floes, medium floes
and puddle bottoms (i.e., mainly by indirect indications), to determine all
major characteristics of the ice cover - position of the drifting and fast ice,
ice concentration, its age categories, forms, rafting and concentration of
hummocks and ridges, stages of melting, open water zones among ice, thickness
and character of the snow cover, pressures, pollution on the ice, amount and
forms of ice of land origin.
Observations were performed
in a strip from 1-20 flight heights (ice edge, boundaries of zones of varying
concentration) up to 2-3 heights (age categories). This is attributed to
different reliability and in general to the possibility for determining some
characteristics or others at large viewing angles. The accuracy and reliability
of assessing the ice cover parameters and characteristics significantly depend
on illumination conditions, horizontal visibility, weather conditions and the
right choice of the flight height for specific conditions.
In connection with the
non-uniform character of the ice cover, the process for determining each
characteristic includes two stages:
- delineation (identification) of ice of a
given type or of ice having the given characteristic,
- a quantitative estimate of the
area of this ice with regard to other ice or to the total sea area
observed.
During
visual ice observations the qualitative and approximate (eye's measurement)
quantitative estimate of ice distribution and its state is made by observer for
all characteristics simultaneously. The observer analyzes and generalizes
varying indications (with rejection of less reliable), determines the
boundaries of zones and makes the necessary statistical processing in mind. In
view of the limited time of flying over each zone, it is obvious that the
observer cannot process all information.
Actually, as a result of
investigating the accuracy of visual airborne observations, significant errors
in quantitative estimates (under unfavourable conditions in the characteristics
themselves) were found. Thus it was found that total and partial concentrations
are determined even by the most experienced observers with a root-mean-square
error of 1.2-2/10. In addition to random mistakes, there is systematic
overestimating of total and partial concentration of multiyear ice also within
up to 2/10.
Due to a limited
observation strip at observations from low heights only 12-20% of the area
under consideration is directly observed which results in considerable errors
at interpolation and extrapolation of boundaries.
Therefore already at
present, visual ice observations play a supplementary role - a detailed
additional examination from icebreaker's helicopters of the recommended route,
as well as observation of some characteristics which cannot yet be observed
instrumentally. In perspective, the need and desirability (including commercial
benefits) of equipping even light aircraft and helicopters with portable SLAR
and SAR, radar thickness meters and other modern remote sensing means is quite
obvious. It will enable the maximum use of the positive properties of visual
and instrumental methods. Such a combination of methods is already now quite
widespread.
If aircraft or a helicopter
is equipped by radar thickness meters, then profile (along the flight route)
measurements of thickness of first-year ice in the 45-250 cm are made with an
accuracy of 10% of thickness. By the character of signals young ice gradations
are assessed, multiyear ice, ice of river origin and regions of intense
hummocking are identified.
Additional equipping of
aircraft by laser profilers allows objective estimates of the surface relief of
multiyear and first-year ice and determination of the number of the e ridges
per unit route.
5. Combined use of
information
Data of previous sections
allow us to assess the composition and accuracy of determining the variables
characterizing the ice cover state on individual charts based on satellite
visible and IR imagery, satellite and airborne SLAR and SAR data and of visual
ice observations data.
Operational individual ice
charts are directly used for shipping support. However, more or less full
understanding of the ice situation can be obtained only from their combination.
Hence in the processing centers composite ice charts are issued on the basis of
individual charts and available additional information (data of ships, polar
stations, expeditions, buoys).
In accordance with the
methods for their preparation, if observations in some observation region were
performed using several remote sensing mans, the largest accuracy can be
assumed to be the accuracy of determination of separate variables. Hence it is
reasonable to present data on the possibility and accuracy of determining ice
cover characteristics in the form of summarized tables.
The accuracy of determining
the age gradation (thickness) of the ice floes depends on the range and
resolution. The range governs the amplitudes of the signals from ice of
different age categories and resolution - the possibility of its use for
interpretation of textural, structural and indirect indications (table 1).
The accuracy of estimating
the main generalized characteristics, the possibility for detecting and
interpretation of ice formations (tables 2 and 3) at their contrast depiction
at the background of other ice or open water mainly depends on resolution.
Table 1. Possibility and accuracy of
determining age (thickness) of the ice floes (cm)
|
|
|
Range, resolution, method |
||||||
|
Characteristic |
Limits of |
Visible |
IR |
Microwave |
Radar |
|||
|
|
values |
0.1-2 m |
0.2- 3 km |
0.2-3 km |
5-20 m |
20-100m |
1.5-3km |
thickness |
|
|
(cm) |
AV |
PV |
PI |
AR, PR |
PR |
meter |
|
|
New ice |
0 |
+ |
- |
- |
- |
- |
- |
X |
|
Nilas |
10 |
3 |
10 |
3 |
3 |
5 |
8 |
X |
|
Grey |
10 - 15 |
8 |
15 |
3 |
3 |
8 |
10 |
XX |
|
Grey-white |
15 - 30 |
8 |
15 |
5 |
8 |
15 |
X |
XX |
|
Thin first-year |
30 - 70 |
20 |
X |
15 |
X |
X |
X |
6 |
|
Medium first-year |
70 - 120 |
30 |
X |
30 |
X |
X |
X |
10 |
|
Thick first-year |
120 - 140 |
60 |
X |
X |
X |
X |
X |
20 |
|
Second-year |
> 200 |
+ |
X |
X |
+ |
+ |
XX |
+ |
|
Multiyear |
> 300 |
+ |
X |
X |
+ |
+ |
XX |
+ |
Note:
- + observed as a specific type, -
unobserved,
- x or xx - no differences in the signals
from ice of these gradations are observed, however, they can be separated
from all other stages of development,
- Data in the IR range correspond to
temperatures less than -20- -30 C in the microwave range
during winter and springs periods.
Table 2. Possibility and
accuracy of determining the main generalized characteristics (tenths or
conventional scale units).
|
Characteristic |
Limits of values |
Ground resolution |
||||
|
|
|
0,1 - 2 m |
5 - 20 m |
20 - 100 m |
0,2 - 1 km |
1,5 - 3 km |
|
Total concentration |
1 - 3 |
1,0 |
0,5 |
0,5 |
- |
- |
|
|
4 - 8 |
1,9 |
1,0 |
1,0 |
1,0 |
1,5 |
|
|
9 - 10 |
0,5 |
0,2 |
0,5 |
1,0 |
1,0 |
|
Partial concentration |
0 - 10 |
1,5 |
1,0 |
1,0 |
1,0 |
1,5 |
|
Rafting |
0 - 10 |
2,0 |
1,0 |
1,0 |
- |
- |
|
Area of hummocks |
0 - 100 |
5 - 6 |
3 - 4 |
5 - 6 |
- |
- |
|
Snow cover |
0 - 8 |
2 - 3 |
1 - 2 |
- |
- |
- |
|
Stages of melting |
0 - 9 |
1 - 2 |
1 - 2 |
2 |
2 - 3 |
2 - 3 |
|
Ice concentration |
0 - 3 |
1,0 |
1,0 |
1 - 2 |
- |
- |
Table 3. The accuracy of determining the
boundaries, ice drift vectors, the possibility for detecting ice formations.
|
Boundaries , drift, |
Ground resolution |
||||
|
ice targets |
0.1-2 m |
5-20 m |
20-100 m |
0.2-1 km |
1.5-3 km |
|
Position of the boundaries, km |
|
|
|
|
|
|
Fast ice, floes, leads |
2 |
0,5 |
0,5 |
2,0 |
6,0 |
|
Zones |
4 |
2 - 3 |
2 - 3 |
4 |
6 - 8 |
|
Ice drift, km |
- |
1,0 |
1,0 |
2,0 |
5,0 |
|
Minimum observed size, m |
|
|
|
|
|
|
Floes |
2 - 20 |
50 |
200 |
2000 |
500 |
|
Leads, cracks with a width of |
2 |
5 |
30 |
300 |
500 |
|
Icebergs |
5 |
15 |
200 |
2000 |
5000 |
|
Drift divides |
- |
+ |
+ |
+ |
+ |
|
Ridged ice |
+ |
+ |
+ |
+ |
- |
|
Ridges |
+ |
+ |
+ |
- |
- |
Note:
- + observed, - unobserved
- The ice drift and drift divides can be
observed at the survey swath more than 50 km.
At
comparatively detailed field of the drift vectors some comparatively slowly
changing characteristics and stable formations earlier observed using the means
operating in other spectral ranges or the means with a small spatial coverage,
but high resolution (SAR and SLAR, thickness meters, laser profilers, visual
observations), can accumulate taking into account shifts of some ice cover
zones for the period from observation to issuing an ice chart.
For this purpose the
composite chart under preparation is compared to the preceding one. In the
zones whose configuration and area has insignificantly changed it is
supplemented by data on stable characteristics and formations which in this
case can be considered directly observed. The following can be plotted on the
chart:
- zones of varying partial concentration of
old ice,
- age gradations, thickness and partial
concentration of first-year ice,
- ice age at the surface of the preserved
leads, fractures and polynyas (taking into account the ice growth),
- icebergs, stamukhas, zones of hummocking,
ridges on fast ice,
- surface structure (hummocks, snow,
pollution on the ice).
Unstable
characteristics such as pressures, open water among ice, position of the ice
edge and boundaries of the zones of different total concentration should not be
taken from the previous chart.
These data on the
information properties of remote sensing means provide a guaranteed possibility
and accuracy of determining the ice cover characteristics at the present time
which should not be considered constant for the future.
With the development of new
technical means operating in the other regions of the electromagnetic wave
spectrum with other polarizations and their combinations, increasing
resolution, validation observations, development and improvement of methods for
automated interpretation they will be probably supplemented and specified.
This evidence is based on
the experience of only the
A PROPOSAL FOR CODING THE POSITIONS OF THE
POINTS IN THE RECTANGULAR COORDINATES, RATHER THAN IN THE GEOGRAPHICAL
COORDINATES
Determination of the
position of the boundaries of zones, linear and point objects by their
geographical coordinates has significant shortcomings (different accuracy of
determining the coordinates by latitude and longitude, especially in the
near-pole regions, formation of the files of databases in the form of different
size trapeze).
In processing of satellite
and airborne video information: geolocation, transformation of images to
cartographic projections and display, maintenance of operational databank
(complexing, updating, calculations and forecasting, etc.) one has to
constantly convert the geographical coordinates to rectangular ones and vice
versa. As a rule, all procedures are performed in the rectangular coordinates
which are then converted to geographical for storage or dissemination to users.
A question arises why the
position of the boundaries and ice formations is not coded at once in
rectangular coordinates? This would allow an additional 10% reduction of
transmitted data, as compared to the CONTOUR-2 format and would significantly
simplify all algorithms and data conversion software.
This proposal was generally
discussed at the Vth session of the WG of specialists on the WMO Project "Global
Digital Sea-Ice Data Bank" (September 24-28, 1995, St. Petersburg,
Russia). The WG requested Prof. A.V. Bushuyev to prepare specific proposals for
further discussion at the WG GDSIDB and the WMO CMM.
1. Proposed chart
parameters
- The position of the ice chart points
(information, boundaries, objects) is governed by the rectangular
coordinates of the chart in a polar stereographic projection, the scale by
parallels of the section 70° of the Northern and Southern Hemisphere of
1:1000000 or in 1 resolution element (1 mm at the geographical chart) 1 km
at the ground.
- The Earth is assumed to be a ball with a
radius R = 6371 km.
- The start of coordinates in the points of
the projection of the North and South Poles is at the section plane.
- The OX axis is directed from pole to
equator along meridian 180°, the OY axis likewise along meridian 270°.
- To eliminate the need to indicate the
digits, the coordinates of the pole are assumed to be equal X = Y = 5000.
The width of the angles of the working square with longitudes 45°, 135°,
225° and 315° is equal to 30, 444°.
2. Solution of standard
problems
Transfer from geographical
to rectangular coordinates is made using the following system of formulas:
The relative direction or
conventional longitude from meridian 180° is calculated
where l - eastern longitude within the
range from 0° to 360°,
[R(1
+ cos(20°)) / m] = D = 12357,784 - constant, F - latitude.
Coordinates of the points
are coded in the whole values of X and Y with rounding off or rejection of
tenths by one eight-digit group where the first 4 figures denote coordinate X
and the last 4 - coordinate Y.
For example: the point
F=81°18' and l = 115°36' is coded as 54064152.
If higher accuracy is
required, for example, for the drift vectors from buoy data, D is multiplied by
10 and coordinates are coded by a 10-digit group in hundred meters.
After conversion of
geographical coordinates into rectangular, the coordinates of the points at a
computer screen or in plotter work space are calculated by deducting
coordinates X, Y of the initial point and multiplying the obtained differences
by the scale coefficient. Data gridding to any rectangular grid point is also
simple.
Data in operational and
regime banks are advisable to store in the form of files of squares of a
certain size, for example, 500 x 500 cells which considerably expedites the search for necessary information. This is also
realized by the proposed system of coding in rectangular coordinates. The
numbers of the least coordinate lines restricting the square in hundreds of the
resolution cells should be assumed to be the numbers of the squares.
Thus the point 54064152 is
located in square 5040.
When forming the files of
squares the description of the boundaries and linear objects should include the
points of their crossing with the boundaries of the squares.
The reverse conversion from
rectangular coordinates X, Y at the chart to geographical is by using the
formulas:
where ( ) - the obtained by formulae (4)
value.
If this proposal is
considered valid, the transfer from the geographical coordinates to rectangular
will not require changes in the general layout of the CONTOUR-2 format, code
tables, constants, identifiers, service and separating symbols.
However, to implement this
proposal it is necessary to agree upon the projection, scale, section parallel,
coordinate axes, coordinates of the initial point (pole) of the chart in whose
system of rectangular coordinates information will be transmitted. Also the
earth's parameters should be agreed upon - the radius if it is assumed to be a
ball, large axis, eccentricity if it is assumed to be a rotation ellipsoid.
In view of a complex
character of this procedure, the proposal for transfer from the geographical
coordinates to rectangular is contained in the Annex to be further discussed.
3. Justification of the
proposed chart parameters
The stereographic
projection by its properties is considered the most suitable for depicting ice
situation for the entire
However, conversion of the
geographical coordinates to rectangular coordinates of the earth's chart as a
spheroid is based on more sophisticated formulas and the reverse conversion is
not resolved at all in the explicit form and can be performed only by a gradual
approximation method. In view of the fact that operational detailed charts and
review charts of large areas can include several thousands of the points, data
processing even by modern high-performance computers will take much time. Hence
it is proposed to assume the earth to be a ball.
The second problem,
probably, to be also discussed, is location of the coordinate axes. In the Ice
Service of the RF meridians 200° and 290° are assumed to be axial, in the