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Thomas Thompson. 1981. Proposed Format for Gridded Sea Ice Information (SIGRID). Unpublished report prepared for the World Climate Programme.
The charts prepared by the various ice services do not all contain the same number of parameters. The resolution and accuracy also vary according to the use for which the charts are intended. A large degree of flexibility has therefore to be built into the design of both code, format and grid. it should allow digitization of historical ice charts as well as current ones in order to obtain a comprehensive computer-compatible sea ice data bank which is currently updated. The SIGRID format is mainly designed to meet larger scale climate requirements but it may also be used by national services for other purposes.
This report concentrates on conventional sea ice parameters as this is considered most important in the light of present operational practices and the large amount of historical sea ice charts that need to be digitized. It is however realized that remote sensing methods are gradually becoming more and more sophisticated and that automatic interpreted remotely sensed data may supplement some of the conventional sea ice parameters. Provisions have therefore been made to allow for these types of data to be included in the code when required.
As the various ice charts do not contain the same number of parameters and as these may have different accuracy and resolution the code has been designed to allow for an arbitrary number of parameters to be digitized. The grid system can further be varied to cover the required resolution. As an example it will be possible to digitize only the total ice concentration with a resolution of say 4 degrees longitude X 2 degrees latitude. It will also be possible to digitize 20 parameters for each grid point with a resolution of for instance 0 degrees, 30 minutes longitude by 0 degrees 15 minutes latitude. The grid will be geographical but it can easily be expanded to a Cartesian if such a requirement occurs.
A magnetic tape containing digitized sea ice data should include Header files and chart data files. The header file will contain information relevant to the whole or major portions of the tape. Each chart data file will contain information relevant to one ice chart and will include a header record, grid line records and data groups. See figure 1.
Organization of digitized sea ice information on magnetic tape
Header File SIGRINF :AAFcFcNNN (:AQcLaLaLaLaLoLoLoLoLo :Bn_n_n_n_n-n:Cd2d2d2d2) :DNtNtPtPt...PtPt
Header Record :EJJJMMYYGGGpGp:FNsNsNs :GNpNpP2P2:HP=P=NpNn Grid Line Record:KZZ:Lmmmppp:MNpNpNp Data Group :NGIRNrNrP2P2
SIGRIDINF - identifier of header file
: - start of a new information group
AA - area or country from which the data originate (See WMO Pub No. 365, Part 11, Attachment 11-6, Table 8)
FcFc - Centre, Service or institution from which the data originate (table to be established)
NN - Catalogue number of grid used (See WMO Pub. No. 9, Volume 3). If the grid specification is not included in this publication, the grid can be defined by the following groups identified by the letters A, B and C. Use in this case NN = 099
( ) - If the grid is specified by means of a WMO catalogue number, groups within parentheses are omitted.
A B C ...R - indicators
QcLaLaLaLaLoLoLoLoLo - latitude and longitude of origo (starting point) of a geographical grid. The grid lines are scanned towards increasing latitudes (south to north in the Northern Hemisphere and north to south in the Southern). The grid points are scanned from west to east along grid lines (applies to the Southern as well as the Northern Hemisphere)
nlnlnl - maximum number of grid lines (along meridian)
npnpnp - maximum number of grid points (along parallels)
dldldldl - mesh width of grid (distance between grid lines along meridians) in degrees and minutes.
NtNt - total number of sea ice parameters occurring on the charts
PtPt...PtPt - identifiers of all sea ice parameters occurring on the charts
SIGRIDNN - identifier of Chart Data File with sequential number (NN)
JJJ - century, decade and year (e.g. 982 = 1982)
MM - month of the year; from 01 to 12
YY - day of the month, from 01 to 31
GG - time of chart in whole hours, GMT
GpGp - period (+/- whole hours)of observations on which chart is based
NsNs - serial number of chart (determined by national centre)
NpNp - number of sea ice parameters included in each grid point without being separately identified in these points (see note 1).
PiPi...PiPi - identifiers of sea ice parameters and order in which they are included in each grid point without being separately identified in these points (see note 1).
PIPI - identifier of sea ice parameters defined individually for actual chart
Np - number of parameters defined by PIPI
Nn - number of digits per parameter defined by PIPI
= - sign that identifies the start of grid line record
ll - longitude/latitude mesh width ratio (example: distance between grid lines (N-S) 2 degrees, distance between grid points (E-W) 4 degrees, ll = 2).
mmmppp - coordinates of first grid point of a grid line, expressed as the number of grid points along the meridian (mmm) and along the parallel (ppp) counted from the origo (the origo has the coordinates 001001)
NpNpNp - number of grid points on grid line
: - start of data group indicator, used to separate data groups
GI - grid subdivision indicator (see Code table 14)
NrNr - number of consecutive grid points for which the identical information is repeated. (The RNrNr should not occur when the information only refers to one point). When, for instance RnrNr = RO2, the actual and the following point contain identical information.
PiPi - identifier of sea ice parameter within a data group. The data group may include one or several sea ice parameters all identified by PiPi, unless all grid points contain the same parameters in which case the parameters are identified in the Header Record (see Note 1).
The sea ice parameters are defined according to the new International System of Sea Ice Symbols. Each parameter is identified in the record by two letters, e.g. CT (total concentration of ice). The first letter identifies the category of the parameter while the second identifies parameters within the category. In the following tables the letters B,C,D,E,L,O,R,S,T and W are used as category indicators; the rest of the alphabet is left for future use.
The letters X, Y and Z are however reserved for use by individual services should they wish to include parameters not contained in the internationally agreed list. The X, Y, and Z may be used together with any other letter of the alphabet. The use of X, Y, Z should be clearly explained in the Tape Header File at the beginning of each tape. The number of parameters defined in the following tables is 53.
The following categories are proposed for general use:
Category Elements Indicator c Concentration, stage of development and form of ice (including strips and patches) D Dynamic processes v Water openings R Topography features E Thickness of ice s Surface features and melting forms B Ice bergs or ice of land origin T Sea surface temperature 0 Source of information on which chart is based L Land area
It should be noted that the recording of parameters on a tape record is less subject to space restrictions as are their coding for telecommunicated reports or plotting in the form of symbols on a sea ice chart. For archiving purposes, there is a greater freedom of choice of the number of digits to be used to record a parameter; this facilitates later processing of the data. Thus, for the recording of for instance, sea ice concentration, two digits are proposed.
The following parameter identifiers are defined:
Coding: CTCC CACaCaSaSaFaFa CBCbCbSbSbFbFb CCCcCcScScFcFc (CFFpFpFsFs) CNSoSo CDSdSd
*Drift of icebergs to be reported under "Icebergs or ice of land origin"
To indicate whether the thickness is estimated or measured, the following convention may be used:
Note: If the temperature is negative, the first digit should be coded by a minus sign.
Grid Line: Line connecting all grid points having the same latitude
Grid Point: A point in the middle of a square or rectangle where the dimension corresponds to the mesh width along parallels and meridians. The distance between the grid points corresponds to the above mesh width. The ice information for a grid point is representative for the grid square in which the grid point lies.
Data Group: Group which contains information on one or several ice parameters relative to one grid point (or several consecutive grid points with identical information on a grid line).
Mesh Width: The length of the sides of the rectangles, in the middle of which the grid point lies. The sides of the rectangle will in most cases have different lengths in a geographical grid (e.g. 2 degrees along parallels and 1 degree along meridians).
Scanning Mode: the order in which the grid points are scanned. In a geographical grid the grid points are scanned along grid lines from west to east (0 to 360 degrees). The grid lines are scanned towards increasing latitudes (south to north in the Northern Hemisphere and north to south in the Southern).
To identify a grid the following information is needed:
Latitude Long/Lat Mesh width along parallels intervals if mesh width along meridians is 60 nm (1 degree lat) 00 - 50 1 60 nm - 39 nm 50 - 75 2 77 nm - 31 nm 75 - 80 4 52 nm - 42 nm 80 - 85 6 63 nm - 31 nm 85 - 87 12 63 nm - 38 nm 87 - 89 20 63 nm - 21 nm 89 - 895 40 42 nm - 21 nm 895 - 90 80 42 nm
Three levels of subdivisions have been provided for, with a view to dividing the original grid square into four, nine or 16 areas according to figure 2. The basic grid may be defined as :first order" and the following finer meshes as second, third and fourth respectively. The number of sub-areas for each of these orders will be 12 =1, 22 =4, 32 =9 and 42 =16.
Example: a geographical grid has a basic mesh width of 1 latitude by 2 longitude; the second order will have 4 grid squares with a mesh width of 1/2 latitude by 1 longitude, the third order 9 grid squares with a mesh width of 1/3 latitude by 2/3 longitude, and the fourth order 16 grid squares with a mesh width of 1/4 latitude by 1/2 longitude. Expressed in degrees and minutes this would be 1 x 2, 30'x 1, 20' x 40', and 15' x 30'. The grid subdivision is indicated by a subdivision indicator which for the basic grid is set to 1, second order to 2, third order to 3 and fourth order to 4.
Figure 2, Subdivision of a Grid Square
SIGRIDINF :NOMI:099:A7670003300:B018036:C0100:D05CTCAWFWDTT SIGRID01 :E97902011200:F009 =K02:L009007:M032 :R02CT92CA929908:RO3CT90:407CT80:N2CT80:CT402F6WD3 :CT00:CT60Wf6WD7:CT00:TT000:TT010:TT015:N2CT10:TT000:TT005 :CT40WF6WD7:CT50WF6WD7:RO3CT80:N2CT40:CT20WF6WD5:CT80:CT70 :CT30WF6WD1:R02 CT20WF6WD2:CT60WF6WD3:CT70:RC2CT90:R02CT80 =K04:L010004:M016 :CT92CA929908:R02CT90:CT90:CT80:CT60WF6WD3:CT0CTT005 :CT01TT005:N2CT0155005:CT40WF6WD4:CT60WF6WD7:CT00 :CT70WF6WD3:R02CT80:CT90:R04CT90 =k04:L011004:M016 :99:99:99
SIGRIDINF :NOMI:099:A7670003300:B018036:C0100:D05CTCAWFWDTT SIGRID01 :E97902011200:F0009:G01CT =KD2:L009007:M032 :R0292CA929908:R0390:R0780:N280:40WF6WD3:00:60WF6WD7:00 :00TT000:00TT01000TT015:N210:00TT000:00TT005:40WF6WD7 :50WF6WD7:R0380:N240:20WF6WD5:80:70:30WF6WD1:R0220WF6WD2 :60WF6WD2:70:R0290:R0280 =k04:L010004:M016 :92CA929908:R0290:90:80:60WF6WD3:00TT005:01TT005:N201TT005 :40WF6WD4:60WF6WD7:00:70WF6WD3:R0280:90:R0490 =K04:L011004:M016 :99:99:99
NO = Norway MI = Meteorological Institute 099 = Geographical Grid with definitions A7670003300 = Coordinates of origo (67 00' N, 3300' W) B0018036 = Maximum number of grid lines (18) and maximum number of grid points along grid line (36) C0100 = Grid mesh (1 degree along meridians) D05CTCAWFWDTT = Total number of parameters digitized (5) and identifiers of these parameters E97902011200 = Date of chart (1 February 1979 12 GMT) F009 = Serial number of chart (no 9/1979) G01CT (example 2) = Number of parameters (1) and parameter not identified in each grid point = = Start of grid line K02 = Ratio between longitude and latitude (2 long/1 lat) L009007 = coordinates of starting point of grid line M032 = number of grid points along grid line : = start of first data group R02 = number of grid points for which the same data apply (two grid points) CT92 (example 1) = total concentration = 10/10 92 (example 2) = total concentration = 10/10 CA92 = Partial concentration of thickest ice = 10/10 99 = stage of development of ice unknown 08 = form of ice = fast ice : = start of second data group (applies to third grid point) R03 = number of grid points for which the same data apply (three grid points) CT90 (example 1) = total concentration = 9/10 90 (example 2) = total concentration = 9/10 : = start of third data group (sixth grid point) RO7 = seven consecutive grid points are identical CT80 (example 1)= total concentration = 8/10 80 (example 2) = total concentration = 8/10 : = start of fourth data group (thirteenth grid point) N2 = grid square subdivided into four subsquares CT80 (example 1)= total concentration in first subsquare = 8/10 80 (example 2) = total concentration in first subsquare = 8/10 : = start of fifth data group (subsquare 2) CT40 (example 1)= total concentration = 4/10 40 (example 2) = total concentration = 4/10 WF6 = form of water opening = ice edge (6) WD3 = orientation of ice edge = SE - NE (3) : = start of sixth data group (subsquare_3) CT00 (example 1)= open water 00 (example 2) = open water : = start of seventh data group (subsquare 4) CT60 (example 1)= total concentration = 6/10 60 (example 2) = total concentration = 6/10 WF6 = form of water opening = ice edge (6) WD7 = orientation of ice edge = NW - SE (7) : = start of eighth data group (fourteenth grid point) CT00 (example 1)= open water 00 (example 2) = open water : = start of ninth data group (fifteenth grid point) 00 (example 2) = open water TT000 = sea surface temperature = 00.0 c
Parameter Parameter(s) Number of Digits per Total number of Identifier Parameters parameter digits CT CC 1 2 2 CA CaCaSaSaFaFa 3 2 6 CB CbCbSbSbFbFb 3 2 6 CC CcCcScScFcFc 3 2 6 CF FpFpFsFs 2 2 4 CN SoSo 1 2 2 CD SdSd 1 2 2 DP dp 1 1 1 DD D 1 1 1 DR ViVi 1 2 2 DO Op 1 1 1 WF Wf 1 1 1 WN No 1 1 1 WD D 1 1 1 WW WwWw 1 2 2 WO Op 1 1 1 RN Rn 1 1 1 RA Ra 1 1 1 RD D 1 1 1 RC CrCr 1 2 2 RF RfRf 1 2 2 RH RhRh 1 2 2 RO Op 1 1 1 RX RIRI 1 2 2 EM tEtEtE 1 3 3 EX txtxtx 1 3 3 EI tntntntxtxtx 2 3 6 EO Op 1 1 1 SC CsCs 1 2 2 SN s 1 1 1 SD D 1 1 1 SM ms 1 1 1 SA mama 1 1 1 SO Op 1 1 1 BL BiBs 1 2 2 BD D 1 1 1 BR ViVi 1 2 2 BN nBnB 1 2 2 BY YY 1 2 2 BO Op 1 1 1 TT TwTwTw 1 3 3 TO Op 1 1 1 OP Op 1 1 1 OS Os 1 1 1 OT Ot 1 1 1 LL 0 0 Total: 46 53 88
BiBs -type and size of iceberg (code table 12)
CC -total concentration of all ice in the area, reported in tenths (code table 1)
CaCa -Partial concentration of respectively thickest, CbCb second thickest and third thickest ice, reported in CcCc tenths (code table 1)
CrCr -concentration of topography features, in tenths (code table 1)
CsCs -concentration of snow coverage in tenths (code table 1)
D -1) Direction of dynamic processes (code table 5) -2) Orientation of water openings (code table 5) -3) Orientation of sastrugies (code table 5) -4) Orientation of topography feature (code table 5) Note: compacting of ice in for instance NE-SW direction is recorded either as 1 or 5
dp -dynamic processes (code table 4)
FaFa FbFb FcFc -form of ice corresponding to SaSa, SbSb, andScSc respectively (code table 3)
FpFp - predominant (FpFp) and secondary (FsFs) form FsFs of ice (code table 3)
MaMa -area coverage of melt water in tenths
Ms -melting forms (code table 11)
No -number of water openings (code table 7)
nBnB -number of icebergs (code table 13) (WMO code 2877)
Op -Observational method for individual parameters (code table 14)
Op -primary (Op), secondary (Os) and tertiary (Ot) Os source of observation on which the ice chart is Ot based (code table 14)
Ea -age of topography feature (code table 9)
RfRf -frequency of topography feature, in number per nautical mile
EhEh -mean height of topography feature, in tenths of meters
RxRx -maximum height of topography feature, in tenths of meters
Rn -nature of topography feature (code table 8)
SaSa -stage of development of respectively thickest, SbSb second thickest and third thickest ice, of which ScSc the concentration is reported by CaCa, CbCb and CcCc respectively (code table 2)
SdSd -stage of development of any remaining class of ice not reported by SaSa, SbSb, ScSc or SoSo (code table 2)
SoSo -stage of development of ice thicker than SaSa but with a concentration less than 1/10 (code table 2)
s -snow depth (code table 10) (WMO code )
TwTwTw -sea surface temperature, in tenths of degrees
tEtEtE -mean thickness of ice in centimeters
tntntn -minimum thickness in thickness interval
txtxtx -maximum thickness of ice, in centimeters
ViVi -rate of ice drift, in tenths of knots
Wf -form of water openings (code table 6)
WwWw -width of water openings, in hundreds of meters
YY -day of month when icebergs were sighted
Ice free 00 Less than 1/10 (open water) 01 Bergy water 02 1/10 10 2/10 20 . . . . . . 9/10 90 more than 9/10 less than 10/10 (9+) 91 10/10 92 concentration intervals ClCh
(Cl = lowest concentration in interval) Ch = highest concentration in interval)
1/10 - 3/10 13
4/10 - 6/10 46
7/10 - 9/10 79
7/10 - 10/10 71
Ice free 00 Ice thickness in cm 01 . . 50 55 cm 51 60 cm 52 65 cm 53 70 cm 54 thickness 80 cm 56 interval, 5 cm 85 57 90 58 95 59 -------------- 100 60 110 61 120 62 130 63 thickness 140 64 interval 10 cm 150 65 160 66 170 67 180 68 190 69 --------------- 200 70 thickness 250 71 interval 50 cm 300 72 350 73 --------------- 400 74 thickness 500 75 interval, 600 76 100 cm 700 77 800 78 --------------- 900 79 No stage of development 80 new ice 81 nilas, ice rind less than 10 cm 82 young ice 10 - 30 cm 83 gray ice 10 - 15 cm 84 gray-white ice 15 - 30 cm 85 first year ice 30 - 200 cm 86 thin first year ice 30 - 70 cm 87 thin first year stage 1 30 - 50 cm 88 thin first year stage 2 50 - 70 cm 89 for later use 90 medium first year ice 70 - 120 cm 91 for later use 92 thick first year ice greater than 120 cm 93 for later use 94 old ice 95 second year ice 96 multiyear ice 97 glacier ice 98 undetermined/unknown 99
Code Figure Pancake ice 30 mm -3 m 00 Shuga/small ice cake, brash ice less than 2 m across 01 Ice cake less than 20 m across 02 Small floe 20 m - 100 m 03 Medium floe 100 m - 500 m 04 Big floe 500 m - 2 km 05 Vast floe 2 km - 10 km 06 Giant floe greater than 10 km across 07 Fast ice 08 Growlers, floebergs or floebits 09 Icebergs 10 Strips and patches 11 Level ice 12 Undetermined or unknown 99
Compacting ice, no intensity given 0 Compacting ice, slight 1 Compacting ice, considerable 2 Compacting ice, strong 3 Diverging ice 4 Shearing ice 5 Ice drift, rate 0,1 - 0,9 knots 6 Ice drift, rate 1,0 - 1,9 knots 7 Ice drift, rate 2,0 - 2,9 knots 8 Ice drift, rate 3,0 knots or more 9
Note: When actual rates of ice drive (ViVi) are given, code figure ViVi = 99 is used for rate unknown
The direction is identified in relation to the grid. In a geographical grid, 1 would indicate northeast, 2 east, 3 southeast, etc.
cracks 1 crack at specific location 2 lead 3 frozen lead 4 polynia ` 5 ice edge 6
1 1 2 2 3 - 5 3 5 - 10 4 > 10 5
rafting 1 hummocks 2 ridges 3 jammed brash barrier 4
New 1 weathered 2 very weathered 3 aged 4 consolidated 5
Code Figure Code Figure
no melt 0 many thaw holes 5 few puddles 1 dried ice 6 flooded ice 3 rotten ice 7 few thaw holes 4 few frozen puddles 8 all frozen puddles 9
Type (Bi) Code Figure Size (Bs) Code Figure
growler and/or bergy bit 1 unspecified 0 iceberg unspecified 2 small 1 iceberg, glacier berg 3 medium 2 iceberg, dome 4 large 3 iceberg, pinnacled 5 very large 4 iceberg, tabular 6 ice island 7 floeberg 8 radar target 9 (suspected iceberg)
visual surface observation 1 visual aircraft observation 2 visual and infrared satellite observation 3 passive microwave satellite observation 4 radar surface or airborne observation 5 radar satellite observation (SAR) 6 laser/scatterometer/sonar 7 data buoys 8 estimated (temporal and/or spatial) 9 unknown 0
second order subdivision (4 squares) 2 third order subdivision (9 squares) 3 fourth order subdivision (16 squares) 4