NOAA KLM User's GuideSection 9.8.4 |
The Aerosol Observation File contains eight days of Sea Surface Temperature (SST) retrievals containing a single-channel (AVHRR Channel 1) optical thickness parameter τA. The SSTs in these retrievals are "aerosol-corrected" SSTs, but the uncorrected SSTs are also contained within the observation. The layout of the file is identical to the SST 8-day observation file with the exception that the 2-bytes used to store a water vapor parameter in the SST retrieval are used for an aerosol optical thickness value and a spare area is used for the uncorrected SST. This data file consists of 4002 physical records each with a length of 13,024 bytes.
The organization of the file is as follows: earth is divided into 5 degree by 5 degree blocks and by 1 degree by 1 degree subblocks within each block. The blocks are numbered from 1 to 2592 with the origin or first block at 180 degrees West or -180 and 90 degrees South or -90. Block numbers increase by 1 to the East and by 72 to the North. To locate information in an area, the block number is found which corresponds to the block encompassing the area. A table in the directory record points to the record which contains the desired block. After locating the record containing the block, another table at the beginning of the record locates the proper location of the desired subblock.
The file has overflow records and as such expands and contracts as data are available.
The first record is the directory record containing the block directory and other information. All other records are data records, each containing a subblock directory followed by observations.
This record describes the size, origin, and location of the blocks making up the file. To calculate the block number of a location (ILAT, ILON) use the following formula:
Where:
NOTE: To find INTEGER ILAT and ILON, round up if positive and down if negative. Each block includes the minimum whole latitude and longitude and excludes the maximum whole latitude and longitude which border the block.
For example: The limits of block 1 are:
Table 9.8.4.2-1 contains the format of the directory record.
| Halfword | Description | Comments |
|---|---|---|
| 1 | Latitude Origin | -90 |
| 2 | Longitude Origin | -180 |
| 3 | Size of block in latitudinal direction | in degrees (currently 5) |
| 4 | Size of block in longitudinal direction | in degrees (currently 5) |
| 5 | First free record pointer | Points to first available record |
| 6 | Number of records in file | Currently 4002 |
| 7 | Halfword number of start of block directory table | Currently 11 |
| 8 | Day of year of latest data | 1-366 |
| 9 | File availability | 0=available 1=unavailable update in progress |
| 10 | Year of century of latest data | 0-99 |
| 11 | Record number for block 1 | 2-4002 |
| 12 | Record number for block 2 | 0 if no data in block |
Table 9.8.4.3-1 contains the format of the data record.
| Halfword | Description | Comments |
|---|---|---|
| 1 | Record number | 2 to 4002 |
| 2 | Block number | 1 to 2592 |
| 3 | Extent number (# of records) removed from primary | 0 if primary |
| 4 | Pointer to succeeding overflow record. Last overflow record points to primary. | 0 if no overflow. |
| 5 | Pointer to halfword position of start of observation data | currently 61 |
| 6 | Pointer to start of subblock directory | currently 11 |
| 7 | Lower left latitude of block | degrees |
| 8 | Lower left longitude of block | degrees |
| 9 | Pointer to last halfword containing data | If no data in the record, this pointer points to the start position of observation data -1 |
| 10 | Unused | . |
| 11 | Halfword of start of data for subblock #1 | 0 if no data for this subblock in this record |
| 12 | Halfword of end of data for subblock #1 | 0 if no data for this subblock in this record. Other extents may or may not contain data for this subblock. |
| 13-60 | Similar to halfwords 11 and 12 for remaining subblocks. | . |
| 61-6512 | Observation data | . |
If the observations for a block cannot fit on one record, as many additional records (extents) are allocated as needed. Each additional record having the subdirectory and subdocumentation included. If the subblock is known to be empty for the current record, 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 is allocated for the remainder of the subblock. Unused portions of the records containing no data are zero filled.
Given IX longitude and IY latitude, the subblock number (SBN) can be calculated as follows:
This assumes all subblocks are 1 degree boxes. Here LLA and LLL are respectively the lower left latitude and longitude for the 5 degree blocks.
Simplifying the above:
Where C = -LLA x LOO - LLL + 1 is previously determined.
Satellite Aerosol/SST Observations are of variable lengths with a minimum length of 28 halfwords (2-byte integer) and a maximum of 48 halfwords. The observation length must be an even number of halfwords with no odd halfword except the first halfword being negative (i.e. the sign bit is 1). The first odd halfword of an observation is always negative. Table 9.8.4.4-1 gives the format for the observations.
| Halfword # | Byte | Quantity | Range |
|---|---|---|---|
| 1 | 1 | Type of Observation (see Table 9.8.4.4-2) | 129 to 255 |
| 1 | 2 | Source of Observation (see Table 9.8.4.4-3) | 0 to 255 |
| 2 | 3 | Year of Century | 0 to 99 |
| 2 | 4 | Month of Year | 1 to 12 |
| 3 | 5-6 | Latitude (+N,-S) x 100 | -9000 to 9000 |
| 4 | 7-8 | Longitude (+E,-W) x 100 | -18000 to 17900 |
| 5 | 9 | Day of Month | 1 to 31 |
| 5 | 10 | Hour of Day | 0 to 23 |
| 6 | 11 | Minute of Hour | 0 to 59 |
| 6 | 12 | Second of Minute | 0 to 59 |
| 7 | 13-14 | Aerosol-corrected SST (degrees C x 10) | -20 to 350 |
| 8 | 15-16 | Reliability | 0 to 32767 |
| 9 | 17-18 | Solar Zenith Angle (degrees x 10) | 0 to 1800 |
| 10 | 19-20 | Satellite Zenith Angle (degrees x 100) (Negative to left of spacecraft track, positive to right.) | -6000 to 6000 |
| 11 | 21-22 | Analyzed Field SST (degrees C x 10) | -20 to 350 |
| 12 | 23-24 | Internal Error (RMS x 100) | 0 to 1000 |
| 13 | 25-26 | Relative Azimuth Angle (degrees x 10) | 0 to 1800 |
| 14 | 27-28 | Climatological SST (degrees C x 10) | -20 to 350 |
| 15 | 29 | Beginning Row of Unit Array | 1 to 11 |
| 15 | 30 | Beginning column of Unit Array | 1 to 11 |
| 16 | 31-32 | AVHRR Channel 1 Average (% x 100) | 0 to 10000 |
| 17 | 33-34 | AVHRR Channel 2 Average (% x 100) | 0 to 10000 |
| 18 | 35-36 | AVHRR Channel 3 Average (K x 100) | 0 to 32767 |
| 19 | 37-38 | AVHRR Channel 4 Average (K x 100) | 0 to 32767 |
| 20 | 39-40 | AVHRR Channel 5 Average (K x 100) | 0 to 32767 |
| 21 | 41-42 | Space View SDEV Channel 1 (% x 100) | 0 to 10000 |
| 22 | 43-44 | Space View SDEV Channel 2 (% x 100) | 0 to 10000 |
| 23 | 45-46 | Space View SDEV Channel 3 (K x 100) | 0 to 32767 |
| 24 | 47-48 | Channel 4 Blackbody Temperature (K x 100) | 0 to 32767 |
| 25 | 49-50 | Channel 5 Blackbody Temperature (K x 100) | 0 to 32767 |
| 26 | 51-52 | Algorithm Number | 1011 to ? |
| 27 | 53-54 | Aerosol Optical Thickness x 1000 | 0 to 2440 |
| 28 | 55-56 | Uncorrected SST (K x 100) | 27116 to 30816 |
|
If HIRS Data is appended: |
|||
| 29 | 57-58 | HIRS Channel 1 Temperature (K x 100) | 0 to 32767 |
| 30 | 59-60 | HIRS Channel 2 Temperature (K x 100) | 0 to 32767 |
| 31 | 61-62 | HIRS Channel 3 Temperature (K x 100) | 0 to 32767 |
| 32 | 63-64 | HIRS Channel 4 Temperature (K x 100) | 0 to 32767 |
| 33 | 65-66 | HIRS Channel 5 Temperature (K x 100) | 0 to 32767 |
| 34 | 67-68 | HIRS Channel 6 Temperature (K x 100) | 0 to 32767 |
| 35 | 69-70 | HIRS Channel 7 Temperature (K x 100) | 0 to 32767 |
| 36 | 71-72 | HIRS Channel 8 Temperature (K x 100) | 0 to 32767 |
| 37 | 73-74 | HIRS Channel 9 Temperature (K x 100) | 0 to 32767 |
| 38 | 75-76 | HIRS Channel 10 Temperature (K x 100) | 0 to 32767 |
| 39 | 77-78 | HIRS Channel 11 Temperature (K x 100) | 0 to 32767 |
| 40 | 79-80 | HIRS Channel 12 Temperature (K x 100) | 0 to 32767 |
| 41 | 81-82 | HIRS Channel 13 Temperature (K x 100) | 0 to 32767 |
| 42 | 83-84 | HIRS Channel 14 Temperature (K x 100) | 0 to 32767 |
| 43 | 85-86 | HIRS Channel 15 Temperature (K x 100) | 0 to 32767 |
| 44 | 87-88 | HIRS Channel 16 Temperature (K x 100) | 0 to 32767 |
| 45 | 89-90 | HIRS Channel 17 Temperature (K x 100) | 0 to 32767 |
| 46 | 91-92 | HIRS Channel 18 Temperature (K x 100) | 0 to 32767 |
| 47 | 93-94 | HIRS Channel 19 Temperature (K x 100) | 0 to 32767 |
| 48 | 95-96 | HIRS Channel 20 Temperature (% x 100) | 0 to 1000 |
| Code | Type |
|---|---|
| 157 | Day Operational Algorithm |
| align="center"158 | Day Operational Algorithm in relaxed cloud mode |
| 167 | Day Test Algorithm |
| 168 | Day Test Algorithm in relaxed cloud mode |
| Code | Source |
|---|---|
| 1 | NOAA-11 AVHRR |
| 3 | NOAA-14 AVHRR |
| 100 | Ship data from Navy (FNMOC) |
| 101 | Buoy data from TIROS collection system |
| 102 | Fixed Weather Ship (from NCEP) |
| 103 | Moving Ship with Name (from NCEP) |
| 104 | Moving Ship without Name (from NCEP) |
| 105 | Fixed Buoy (from NCEP) |
| 106 | Drifting Buoy (from NCEP) |
| 107 | XBT (from NCEP) |
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