NOAA KLM User's GuideSection 9.1.2 |
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:

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:

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.
| 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.
| Halfword # | Contents | Range |
|---|---|---|
| 1 | Record number | 2 to 8446 |
| 2 | Block number | 1 to 2592 |
| 3 | Extent number (number of records removed from primary) | 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.
| 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 |
| 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. | |
| 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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