NOAA KLM User's Guide

Section 9.1.2

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9.1.2 Eight-Day SST Observation File

The current operational technique for calculating SSTs is a multichannel technique with separate algorithms for day and night observations. This multichannel technique yields an improved resolution of 8 km. The SST Observation File contains eight days of SST observations, which are organized in 5 x 5 degree blocks. These 5 x 5 degree blocks are further subdivided into 1 x 1 degree subblocks. Global coverage requires 2,592 blocks. The block number IBLOCK for an observation located at ILAT latitude (+N,-S) and ILONG longitude (+E,-W) can be calculated using the following equation:

IBLOCK={(ILAT-LA)over LAO }x INBC +{ (ILONG-LO) over LOO}+1

where LA is the latitude origin of the file (-90 degrees), LO is the longitude origin of the file (-180 degrees), LAO is the size of the block in the latitudinal direction (5 degrees), LOO is the size of the block in the longitudinal direction (5 degrees), and INBC is the number of column blocks (360 degrees/LOO). Each block includes the minimum whole latitude and longitude, and excludes the maximum whole latitude and longitude which borders the block. For example, the limits of Block 1 are: -90.0S to -85.01S and -180.0W to -175.01W. Since all subblocks are 1 degree boxes, the Subblock number SBN for a given latitude and longitude can be defined as:

SBN=(ILAT-LLA) x LOO + ILONG - LLL +1

where LLA and LLL are respectively the lower left latitude and longitude of the 5 degree block.

The first record in the Eight Day SST Observation File is the Block Directory which contains 13,024 bytes. The format of the Block Directory is contained in Table 9.1.2-1.

Table 9.1.2-1. Format of the Block Directory record.
Halfword # Contents
1 LA, the latitude origin of the file (range: -90)
2 LO, the longitude origin of the file (range: -180)
3 LAO, size of block in latitudinal direction (range: +5)
4 LOO, size of block in longitudinal direction (range: +5)
5 First free record pointer (points to record # of first record available as an overflow track, 0 if no more tracks available).
6 Number of records in file (3,100 initially)
7 Start of Block Directory Information in halfwords (11 initially)
8 Day of year of most recent information (range: 1-366)
9 File availability: 0=available, 1=unavailable, update in progress
10 Year of century of last data (range: 0-99)
11 Record number for Block 1 (range: 2-3,100)
12 Record number for Block 2 (0 for no data in block)
... ...

Using the block number, the record number can be calculated and found in the portion of the Block Directory which serves as a lookup table. If the record number entry is zero, there is no data for that corresponding block in the file. The record number points to the Observation Data record, of which the first portion is a subdirectory. The file contains 8,446 records of 13,024 bytes each. The Observation Data record has the format shown in Table 9.1.2-2.

Extent number (number of records removed from primary)
9.1.2-2. Format of Observation Data Record.
Halfword # Contents Range
1 Record number 2 to 8446
2 Block number 1 to 2592
3 0 (if primary)
4 Pointer to succeeding overflow record. Last overflow record points to primary record. 0 if no overflow
5 Pointer to halfword position of start of Observation Unit 61
6 Pointer to start of Subblock Directory 11
7 Lower left latitude of block LLA (+N,-S) in degrees -90 to +90
8 Lower left longitude of block LLL (+E,-W) in degrees -180 to +180
9 Pointer to last halfword containing data 1 to 6512
10 Unused n/a
11 Halfword of start of data for Subblock #1 0 if no data for subblock; 61 otherwise
12 Halfword of end of data for Subblock #1 (other extents may or may not contain data for this subblock). 1 to 6512
13-60 Similar to halfwords 11 and 12 for remaining subblocks 1 to 6512
61-6512 Observation data (observation units are variable length but usually they are 56 bytes each) n/a

If the block size is changed in the future, a block may contain a different number of subblocks, thus changing the number of subblock pointers and the starting halfword of the Observation Unit. If the observations for a block do not fit on one record, then as many records (extents) are allocated as needed. Each additional record will include the subdirectory and Observation Unit. If the subblock contains no information, then the start and end position contain a zero. Subblocks may cross record boundaries. If an entire subblock cannot fit into one record, it will be split and a new record will be allocated for the remainder of the subblock. Unused portions of records and records containing no data will be zero filled.

The Observation Unit for the Eight Day SST Observation File is of variable length, ranging from a minimum of four 4-byte words to a maximum of 24 words. The length must be an even number of full words with no odd full word (except the first word which is always negative). The first three words of an Observation Unit contain identification information including the type of algorithm used, the satellite, date, time, and location. The fourth word contains the actual SST data and the reliability assigned to the observation. The remainder of the Observation Unit is unique to the type of algorithm used. The format of the Eight Day SST Observation Unit is contained in Table 9.1.2-3. Tables 9.1.2-4 and 9.1.2-5 contain the SST Observation types and source codes, respectively.

Table 9.1.2-3. Format of the Eight Day SST Observation Unit.
Halfword# Byte # Contents Range
1 1 Type of Observation (Table 9.1.2-4) 129 to 255
1 2 Source of Observation (Table 9.1.2-5) 0 to 255
2 3 Year 0 to 99
2 4 Month 1 to 12
3 5-6 Latitude (+N,-S) x 100 -9000 to 9000
4 7-8 Longitude (+E,-W) x 100 -18000 to 17999
5 9 Day 1 to 31
5 10 Hour 0 to 23
6 11 Minute 0 to 59
6 12 Second 0 to 59
7 13-14 SST (degrees C x 10) -20 to 350
8 15-16 Reliability 0 to 32,767
9 17-18 Solar zenith angle (degrees x 10) 0 to 1800
10 19-20 Satellite zenith angle (degrees x 10) -600 to 600
11 21-22 Analyzed Field SST (degrees C x 10) -20 to350
12 23-24 Internal Error (RMS x 100) 0 to 1000
13 25-26 Solar azimuth angle (degrees x 10) 0 to 1800
14 27-28 Climatological SST (degrees C x 10) -20 to 350
15 29 Beginning Row if unit array 1 to 11
15 30 Beginning Column of unit array 1 to 11
16 31-32 AVHRR Ch. 1 average (% x 100) 0 to10,000
17 33-34 AVHRR Ch. 2 average (% x 100) 0 to 10,000
18 35-36 AVHRR Ch. 3 average (K x 100) 0 to 32,767
19 37-38 AVHRR Ch. 4 average (K x 100) 0 to 32,767
20 39-40 AVHRR Ch. 5 average (K x 100) 0 to 32,767
21 41-42 Space View σ Ch. 1 (% x 100) 0 to 10,000
22 43-44 Space View σ Ch. 2 (% x 100) 0 to 10,000
23 45-46 Space View σ Ch. 3 (K x 100) 0 to 32,767
24 47-48 Ch. 4 Blackbody temperature (K x 100) 0 to 32,767
25 49-50 Ch. 5 Blackbody temperature (K x 100) 0 to 32,767
26 51-52 Year of observation 1998 to 32767
27 53-56 Spares n/a

Table 9.1.2-4. SST Observation Types.
Code Type
151 AVHRR-only day operational
152 AVHRR-only night operational
153 HIRS-only day operational
154 HIRS-only night operational
155 AVHRR + HIRS day operational
156 AVHRR + HIRS night operational
157 Aerosol Retrieval - (AVHRR-only day operational)
158 Aerosol Retrieval - (AVHRR-only day operational - warm spot mode)
159 AVHRR-only day operational warm spot mode (relaxed visible cloud test)
160 Reserved
161 AVHRR-only day test
162 AVHRR-only night test
163 HIRS-only day test
164 HIRS-only night test
165 AVHRR + HIRS day test
166 AVHRR + HIRS night test
167-168 Reserved
169 AVHRR-only day test - warm spot mode (relaxed visible cloud test)
170-178 Reserved
179 ITOS SST
180-199 Reserved
200 Independent SST (Ship or buoy)
201-254 Reserved
255 Erroneous Data - Do not use this Observation
Note: Codes having values between 151 and 169 (inclusive) indicate a multichannel technique in use at the present time.

Table 9.1.2-5. SST Observation Source Codes.
Source code Source

128

No source
129 TIROS-N
130 NOAA-61
131 Not Used
132 NOAA-7
133 Not Used
134 NOAA-81
135,72 NOAA-9
8 NOAA-101
1 NOAA-11
5 NOAA-12
2 NOAA-133
3 NOAA-14
4 NOAA-15
5-20 TBD
21-50 Reserved
51 ITOS NOAA-1 Sensor # 1
52 ITOS NOAA-1 Sensor #2
53 ITOS NOAA-1 Sensor # 1
54 ITOS NOAA-2 Sensor #2
55-58 ITOS NOAA-3 and -4
59-62 ITOS NOAA-5
63-127 Reserved
1 No SSTs were archived for these satellites.
2 NOAA-9 source code was 135 prior to August 4, 1986. NOAA-9 source code was 7 beginning on August 4, 1986.
3 No SSTs were ever generated for this satellite.

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