NOAA Polar Orbiter Data User's Guide

Section 5.2.1

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5.2.1 SST Field Format

All of the SST Field products (14-km gridded, 50-km gridded, and 100-km gridded) are derived from the basic 8-km SST observations. An SST Field consists of a specific set of information pertaining to global latitude and longitude intersections. Files have been generated for 0.125 degree, 0.5 degree, and 1 degree latitude-longitude resolution (or 14-km, 50-km, and 100-km resolution, respectively). The Global-Scale (1 degree resolution) file includes the area from 180W to 179E longitude and from -70S to 70N latitude. Using the SST observations as input, NESDIS produces Regional-Scale (50-km) SST analyses and Local-Scale (14-km) SST analyses twice weekly by analyzing all the SST observations obtained during the period since the last analysis.

All resolution field (accumulation) files consist of a Directory Record and a Field Documentation Record, followed by Field Data Records for each field in the accumulation file. Each file (except the Header File) begins with a Directory Record which points to the Field Documentation Record for each field in the file. Details of the Directory Record are contained in Section 5.2.1.1. The Field Documentation Record is described in Section 5.2.1.2, and is always followed by a Field Data Record for each latitude or row of the field. The Field Data Record is described in Section 5.2.1.3.

The fields will generally be arranged in chronological order. A field for a particular day may be missing or repeated so one should examine the Field Documentation Record for each field in the file to find that field spanning the time of interest. The Field Documentation Record (the first record of each field) should be used in referencing the data record for the field since it provides information concerning the organization, size, and time period of the field.

After the Directory Record, there are NFIELDS fields. The first record of each field is a Field Documentation Record which is followed by NRECS Field Data Records, one for each latitudinal row in the field. Each row consists of 28 bytes of information for each longitude or column forming a grid intersection plus 28 bytes at the end of the record (the Latitudinal Row Identifier) containing the row number identification and the date and time of the last analysis made for the field.

Prior to November 1, 1984, a 500-km gridded SST (Climatic-Scale Analysis) product was generated and included with the 50-km gridded fields on the monthly tape. This tape contained five files, the first being the Header File previously described in Table 5.2-1. The second file contained 36 500-km daily fields organized chronologically. The 500-km fields contained 72 grid intersections in each row, one for each 5 degrees of longitude from -180W eastward to 175E. The first physical record of the second file was the Directory Record which pointed to the beginning address of each of the 36 fields. Each field consisted of 30 logical records of 2044 bytes each, blocked into five 12,264-byte physical records. Since there were 36 fields, the data spanned slightly more than a month. The third, fourth, and fifth files of this tape (prior to November 1, 1984), contained 50-km gridded SST fields. The October 1984 archive tape was the last tape to contain a file of 500-km fields.

The third file of the 50-km and 500-km tape (second file after October 1984) contained the 50-km field data for Region 1 from 5N through 53N by -100W through -52W in five weekly fields organized chronologically. The first physical record of the third file was the Directory Record which pointed to the beginning of each of the five fields. Each field had 98 logical records of 2,744 bytes each, blocked into physical records of 10,976 bytes. There were 491 logical records blocked into 123 physical records in this file. The fourth and fifth files (third and fourth after October 1984) contained the 50-km gridded fields for Regions 2 and 3, covered by 15N through 63N by -145W through -97W, and 15N through 63N by 170E through -142W, respectively. They were identical to the third file in organization, but differed in the number and size of records in each file. The third file contained a region with 97 grid intersections per row, one for each .5 degrees of longitude from -100W eastward to -52W. Similarly, the fourth and fifth files had the same number of grid intersections per row, but different longitude ranges from -150W to -70W and 155E to -142W, respectively. The fourth file had five fields with each field having 62 logical records of 4,536 bytes and the fifth file had 5 fields with each field having 62 logical records of 3,416 bytes.

Before April 2, 1996, the 50-km gridded SST files were archived to tape twice each month. Beginning April 2, 1996, these 50 km gridded SST field accumulation files are archived to tape once a month (on the second day of each month) for the previous month and the field accumulation files have been enlarged. File 1 remains a header file while files 2-6 continue to contain the field files. Each field file contains 10 fields (instead of 5) which results in an increase in the number of records in each file. These fields are produced twice a week by analyzing all the SST observations obtained since the last analysis. Prior to August 1, 1986, the 50-km gridded fields were generated for three regions with grid points at every .5 degree latitude/longitude intersection as described above. After August 1, 1986, they were produced for five regions which are defined in Table 5.2.1-1:

Table 5.2.1-1. Areas of 50-km gridded SST fields after August 1, 1986.
Region 1: 5N through 53N latitude
-100W through -52W longitude
Region 2: 15N through 63N latitude
-145W through -97W longitude
Region 3: 15N through 63N latitude
+170E through -142W longitude
Region 4: -35S through 20N latitude
-150W through -70W longitude
Region 5: -35S through 20N latitude
+155E through -145W longitude

The 50-km gridded SST product (after August 1, 1986) contains six files. The first file is the Header File, and files 2 through 6 contain 50-km fields for Regions 1 through 5, respectively. These files are organized in the same manner as the 50-km gridded fields for three regions as previously described.

Before March 2, 1996, the 100-km SST field has the following structure. There are two files, the first being the Header File. In File 2, after the Directory Record, there are 20 fields, 142 physical records per field. The Field Documentation Record is followed by 141 Field Data Records, one for each 1 degree latitudinal row from -70S to 70N. There are 360 grid intersections in each row, one for each l degree of longitude from -180W eastward to 179E. Currently, each Field Data Record contains 2841 logical records with a maximum of 30,520 bytes.

Beginning March 2, 1996, the 100-km SST field tape is generated monthly (on the second day of the month). The tape still contains two files: file 1 is a header file, file 2 is an archive of the 100-km SST field accumulation file. However, file 2 contains 35 fields, but continues to have the same file organization as before (i.e., the directory record structure, the file record length and the format of each field have not changed). Only the number of fields and therefore the number of records in file 2 has increased.

The 14-km gridded SST fields (Local-Scale Analyses) are archived monthly on two tapes. There are eight 0.125 degree resolution fields over the areas shown in Table 5.2.1-2.

Table 5.2.1-2. Areas of 14-km gridded SST fields.
Region 2: 18N through 31N latitude
-98W through -80W longitude
Region 4: 39N through 52N latitude
-136W through -123W longitude
Region 5: 28N through 41N latitude
+155E through -145W longitude
Region 6: 30N through 36N latitude
-82W through -60W longitude
Region 7: 18N through 32N latitude
-85W through -70W longitude
Region 10: 50N through 62N latitude (Seasonal)
-160W through -126W longitude
Region 11: 50N through 70N latitude (Seasonal)
-180W through -157W longitude
Region 12: 20N through 32N latitude
-136W through -105W longitude

The first tape of the 14-km gridded SST field data contains Regions 2, 4, 5, 6, and 7 which cover the Gulf of Mexico, Northwest Pacific coast, Southwest Pacific coast, Northeast Atlantic coast, and Southeast Atlantic coast, respectively. This tape contains six files, the first file being the Header File. The second file contains the 14-km field data for Region 2. There are twelve weekly fields organized chronologically. The first record of each field data file is a Directory Record which points to the beginning of each of the twelve fields. Each field consists of 1273 logical records of 4060 bytes blocked into 12,180-byte physical records. There are 1,273 logical records blocked into 426 physical records in this file. The third file contains 14-km field data for Region 4. Each field in the third file consists of 1,273 logical records of 2,968 bytes blocked into 11,872-byte physical records. There are a total of 1,273 logical records blocked into 321 physical records in the file. The fourth file contains 14-km field data for Region 5. Each field consists of 1,273 logical records of 4,984 bytes blocked into 9,968-byte physical records. There are 1,273 logical records blocked into 640 physical records in this file. The fifth file contains 14-km field data for Region 6. Each field consists of 1,561 logical records of 4,984 bytes blocked into 9,968-byte physical records. There are a total of 1,561 logical records blocked into 784 physical records in this file. The sixth file contains 14-km field data for Region 7. Each field consists of 1,369 logical records of 3,416 bytes blocked into 10,248-byte physical records. There are a total of 1,369 logical records blocked into 460 physical records in this file.

The second tape of the 14-km gridded SST data contains Regions 10, 11 and 12 which cover the Gulf of Alaska, Bering Sea and the Gulf of California, respectively. This tape contains four files, the first file being the Header File which has already been described. The second file contains the 14-km field data for Region 10. This file contains twelve weekly fields organized chronologically. The first record in each field data file is a Directory Record which points to the beginning of each of the twelve fields. Each field consists of 1,177 records of 7,672 bytes each. The third file contains 14-km field data for Region 11 and has the same format as the second file except each field consists of 1,945 records of 5,208 bytes each. The fourth and file contains 14-km data for Region and is identical to the second file in organization except the record size is 7,000 bytes.

5.2.1.1 Directory Record Format

A Directory Record is always the first record of each SST Field File (except the Header File). It has a variable length with zero fill to the logical record size of the type of field, and serves as a pointer to the beginning of each field. Table 5.2.1.1-1 contains the format of the Directory Record.

Table 5.2.1.1-1. Format of the Directory record for the SST Field file.
Full Word # Content
1 Number of records in the data set
2 Number of records in each field (NRECS)
3 Number of fields in the accumulation file (NFIELDS)
4 Field number of latest field entered in accumulation file
5 Record number of first record of Field #1
6 Record number of first record of Field #2
... ...
4+NFIELDS Record number of first record of Field # NFIELDS

5.2.1.2 Field Documentation Record Format

The format of the Field Documentation Record is described in Table 5.2.1.2-1. There are 158 words of information in the Field Documentation Record with blank fill to the logical record size of the particular kind of field. The minimum size is 158 words (632 bytes) and the maximum size is 2,527 words (10,108 bytes). It has the following format (where R or I indicates real or integer words, respectively):

Table 5.2.1.2-1. Format of the Field Documentation Record.
Word # Parameter R or I Description
1 LDBGN I Record number of the first row of the field (currently 2 for all fields since the documentation record requires only one record).
2 SMGLAT R Minimum latitude included in field which is the bottom edge and first row of field (-South; + North).
3 AXLAT R Maximum latitude included in field which is the top edge and last row of field (-South; + North).
4 SMLONG R Minimum longitude included in field which is the left edge and first column of field (-West; + East).
5 AXLONG R Maximum longitude included in field which is the right edge and last column of field (excluding the I.D. column) (-West;+East).
6 RES R Number of latitude-longitude degrees between each grid point.
7 SMHOUR R Youngest time, in hours of the year, of observations used during last analysis, which becomes the oldest time allowed for the next analysis.
8 HOURS R Oldest time, in hours of the year, of observations used during last analysis.
9 TIMGAP R Number of hours between youngest and oldest times of observations used in analysis.
10 MAXDAT I Maximum number of hours allowed in time period for observation times to be included in analysis.
11 SMREL R Minimum reliability of observations to be used in analysis.
12 AXREL R Maximum reliability of observations to be used in analysis.
13-22 SORC(10) R List of source codes of observations to be used in analysis. (See Table 5.2.2.1-6)
23-32 OBTYPE (10) R List of observation types allowed to be used in analysis. (See Table 5.2.2.1-5)
33 NROWS I Number of rows (latitudinal parallels) included in field, excluding documentation record.
34 NCOLS I Number of columns (longitudinal meridians) in field, including the I.D. column.
35 IBLK I Number of rows or logical records per physical block.
36 NWRDS I Number of full words (32 bits) allocated to each grid point.
37 ISZ I Number of rows to be maintained in an array in core for temperature analysis and calculation of gradients.
38 ICENT I Center line within the array of ISZ rows upon which calculations will be performed.
39-41 LWT, LNT, LBT I Word number, length in bits, and starting bit location of analysis temperature within a grid intersection information unit of an SST field.
42-44 LWG, LNG,LBG I Word number, length in bits, and starting bit location of average gradient.
45-47 LWGXP, LNGXP, LBGXP I Word number, length in bits, and starting LBGXP bit location of gradient X+ direction.
48-50 LWGXN, LNGXN, LBGXN I Word number, length of bits, and starting LBGXN bit location of gradient X- direction.
51-53 LWGYP, LNGYP, LBGYP I Word number, length in bits, and starting LBGYP bit location of gradient Y+ direction.
54-56 LWGYN, LNGYN, LBGYN I Word number, length in bits, and starting LBGYN bit location of gradient Y- direction.
57-59 LWPD, LNPD, LBPD I Word number, length in bits, and starting LBPD bit location of Physiographic Description.
60-62 LWNO, LNNO, LBNO I Word number, length in bits, and starting LBNO bit location of Number Observations.
63-65 LWAGE, LNAGE, LBAGE I Word number, length in bits, and starting LBAGE bit location of Age of most Recent Observations.
66-68 LWREL, LNREL, LBREL I Word number, length in bits, and starting LBREL bit location of Reliability.
69-71 LWCLS, LNCLS,
LBCLS
I Word number, length in bits, and starting LBCLS bit location of Class 1 coverage.
72-74 LWSXP, LNSXP, LBSXP I Word number, length in bits, and starting LBSXP bit location of Spatial Covariance X+.
75-77 LWSXN, LNSXN, LBSXN I Word number, length in bits, and starting LBSXN bit location of Spatial Covariance X-.
78-80 LWSYP, LNSYP, LBSYP I Word number, length in bits, and starting LBSYP bit location of Spatial Covariance Y+.
81-83 LWSYN, LNSYN, LBSYN I Word number, length of bits, and starting LBSYN bit location of Spatial Covariance Y-.
84-86 LWIND, LNIND, LBIND I Word number, length in bits, and starting LBIND bit location of Independent Temperature.
87-96 GRDWTS (10) R Weight assigned to each grid unit, according to its distance from the grid intersection for which gradients are being calculated.
97 NP I Number of grid points to be used in calculation of gradients.
98-117 KMDST (10,2) I Look up table of gradient values and corresponding distances to be used in determining the search area for analysis.
118 MKM R Number of paired entries in KMDST.
119-138 H(10,2) R Look up table of gradient values and corresponding factors to be used in determining the new weight assigned to the observation temperature analysis.
139 MH I Number of paired entries in H.
140 EXP R Exponent used in temperature analysis.
141 FDX R Factor used in determining new weight assigned to the observation temperature for analysis.
142 XCLASS R Factor used to place gradients into a class for Gradient Class Summary.
143 DEL R Maximum number of degrees Centigrade (x 10) that the new analysis temperature may differ from the previous SST field temperature.
144 MF I Factor applied to the previous field temperature and reliability to determine the final analysis temperature and its reliability.
145 MSTAR I Factor applied to the combined observation temperature and weight in determining the new analysis temperature.
146 MNSRCH I Minimum distance in kilometers to be searched for analysis observations.
147 MXSRCH I Maximum distance in kilometers to be searched for analysis observations.
148 BDEL R Maximum distance in kilometers to be searched for analysis observations. Maximum difference allowed between new analysis temperature and the previous one for Class 1 coverage bit to be set to 1.
149 FCWT R Maximum value that can be assigned as the reliability of the new analysis temperature.
150 IYYY I Year of youngest time of observation data used (0-99).
151 IYMM I Month of youngest time of observation data used (1-12).
152 IYDD I Day of youngest time of observation data used (1-31).
153 IYHH I Hour of youngest time of observation data used (0-23).
154 IOYY I Year of oldest time of observation data used (0-99).
155 IOMM I Month of oldest time of observation data used (1-12).
156 IODD I Day of oldest time of observation data used (1-31).
157 IOHH I Hour of oldest time of observation data used (0-23).
158 ICURTM I Last time used in analysis (in Julian days from January 1, 4713 BC).

5.2.1.3 Field Data Record Format

Each Field Data Record (latitudinal row) consists of a series of grid intersection points. These points are 28 bytes in length. Each longitude (column) reflects one grid intersection. At the end of the data record (i.e., immediately following the last column) is the 28-byte Latitudinal Row Identifier. All parameters in the grid intersection are stored as integer values and have the format shown in Table 5.2.1.3-1. Note: Climatology values are available in global SST fields only.

Table 5.2.1.3-1. Format of the parameters in the grid intersection.
Word # Byte # Description Units Range
1 1-2 Analysis Temperature C (x 10) -850 to +610
1 3-4 Average Gradient C/100 km (x 10) 0 to 300
2 5-6 Gradient X+ C/100 km (x 10) 0 to 300
2 7-8 Gradient X- C/100 km (x 10) 0 to 300
3 9-10 Gradient Y+ C/100 km (x 10) 0 to 300
3 11-12 Gradient Y- C/100 km (x 10) 0 to 300
4 13 Physiographic Descriptor 0 = sea; 1=land 0 to 15
4 14 Spare Undefined Blank
4 15 Number of Observations Integer 0 to 255
4 16 Age Recent Observations Hours 0 to 255
5 17-18 Reliability Integer 0 to 32767
5 19-20 Class 1 Coverage Bits 0 or 1
6 21 Spatial Covariance X+ Grid units 0 to 10
6 22 Spatial Covariance X- Grid units 0 to 10
6 23 Spatial Covariance Y+ Grid units 0 to 10
6 24 Spatial Covariance Y- Grid units 0 to 10
7 25-26 Climatological Temperature C (x 10) -850 to +610
7 27-28 Spare Undefined Blank

The format of the Latitudinal Row Identifier (last 28 bytes of a row) is contained in Table 5.2.1.3-2. All parameters in the table are stored as integer values. Words 5 through 7 are the date and time at which analysis was performed.

Table 5.2.1.3-2. Format of the Latitudinal Row Identifier.
Word # # Bytes Description Units Range
1 4 Row Integer 1-141
2 4 Spare Undefined 0 to 232
3 4 Spare Undefined 0 to 232
4 1 Physiographic Descriptor Integer Always 255
4 3 Spare Undefined 0 to 224
Date and time at which analysis was performed:
5 4 Hour of Day, Minutes of hour 100 x hours + minutes 100 x (0-23) + (0-59)
6 4 Day of Year Days 1-366
7 4 Year (2-digit) Years 0-99

The terms used to describe the grid intersection points are defined as follows:

ANALYSIS TEMPERATURE - The latest sea surface temperature calculated based on the previous analysis temperature, weighted according to its reliability combined with a weighted average of current observations within a surrounding area which is determined according to the grid points gradient.

AVERAGE GRADIENT - The average of the gradients in all four directions (N, S, E, W) from the grid intersection.

GRADIENT IN X+ DIRECTION - Change in temperature between the grid point and neighbor points within the field in the positive direction along the X axis.

GRADIENT IN X- DIRECTION - Change in temperature in the negative direction along the X axis.

GRADIENT IN Y+ DIRECTION - Change in temperature in the positive direction along the Y axis.

GRADIENT IN Y- DIRECTION - Change in temperature in the negative direction along the Y axis.

PHYSIOGRAPHIC DESCRIPTOR - The land/sea tag indicating whether a grid intersection is a land or sea point.

SPARE - Unused parameter.

NUMBER OF OBSERVATIONS - The total number of current observations used in the analysis of the new temperature for the grid intersection.

AGE OF MOST RECENT OBSERVATION - The age, in hours from the time of last analysis, of the most recent observation used to determine the new temperature for a grid intersection.

RELIABILITY - New reliability associated with the new temperature, based on the previous reliability combined with the weighted reliability of all observations used in the last analysis. Larger values are more reliable.

CLASS 1 TEMPORAL COVERAGE - Set of bits (0-15) of which Bit 1 is set to 1 for each analysis which included observations with a reliability greater than or equal to a specific minimum reliability considered as Class 1. Bit 0 always remains a 0, and all bits are shifted right during each analysis leaving Bit 1 to 0 when no Class 1 reliability observations are used for a grid intersection.

SPATIAL COVARIANCE X+ - The distance in grid units from the grid intersection to the nearest land mass in the positive direction along the X axis.

SPATIAL COVARIANCE X- - The distance in grid units from the grid intersection to the nearest land mass in the negative direction along the X axis.

SPATIAL COVARIANCE Y+ - The distance in grid units from the grid intersection to the nearest land mass in the positive direction along the Y axis.

SPATIAL COVARIANCE Y- - The distance in grid units from the grid intersection to the nearest land mass in the negative direction along the Y axis.

CLIMATOLOGICAL GRID TEMPERATURE - The average sea surface temperature of a grid intersection for a particular month over a number of years, taken from the global climatology file (for the global field files only).

Amended January 21, 2000


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