NOAA KLM User's Guide

Section 9.8.1

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9.8.1 Aerosol Daily Summary File

The Aerosol Daily Summary File contains statistical information pertaining to aerosol observations in each of the earth's 648 (10 degrees x 10 degrees ) Lat/Long boxes. File Structure Description

The first record is a directory record and all other records are data records. There are 41 records in the file. Directory Record Format

The directory record contains information about the time of the data in the file and pointers to the data records for particular Julian Days. Table contains the directory record format.

Table Aerosol Daily Summary Directory Record Format.
Halfword Quantity Range
1 # of records in the file 41 (initially)
2 Year of most recent data in the file 0-32767
3 Record number updated most recently 1-41
4 Julian day of data in first data record 1-366
5 Julian day of data in second data record 1-366
6 to N + 3 Julian day of data in the 3rd through Nth data record 1-366 Data Record Format

Each data record contains all data for a particular day. There are 648 blocks of information (1 block for each 10 degrees x 10 degrees Lat/Long box on the globe). Each block is 20 bytes long and thus each record is 20 x 648 or 12,960 bytes in length. The blocks are organized within each data record sequentially from West to East with the first block containing statistics from the box enclosed by -90.00 to -80.01 degrees latitude (-S, +N) and -180.00 to -170.01 degrees longitude (-W, -E). The second block has statistics from the next box to the east or the box bounded by -170.00 to -160.01 degrees longitude and -90.00 to -80.01 degrees latitude. The 37th block therefore contains statistics for the box -180.00 to -170.01 degrees longitude and -80.00 to -70.01 degrees latitude.

To calculate the starting byte number for the 20-byte block of statistics for a particular (10 degrees x 10 degrees ) box within a data record, the following formula can be used:

Starting Byte # = (36 x (LLLA-OLA)/10 + (LLLO-OLO)/10) x 20 + 1, where:

LLLA = Lower left latitude of desired (10x10 degrees ) box
LLLO = Lower left longitude of desired box
OLA = Latitude of file origin = -90.00
OLO = Longitude of file origin = -180.00

The documentation record is contained in a 20-byte block as shown in Table

Table Aerosol daily summary file documentation record format.
Halfword # of Bytes Quantity Range
1 2 Number of observations in the box 0-32767
2 1 Maximum Optical Thickness (OT) for the box (x 100) 0-244
2 1 Minimum OT for the box (x 100) 0-244
3-4 4 GMT of maximum OT value. (Hours x 10,000) + (minutes x 100) + seconds. 0-235959
5 2 Latitude of observation with maximum OT value. (Degrees x 100) -9000 to 9000
6 2 Longitude of observation with maximum OT value. (Degrees x 100) -18000 to 18000
7 1 Spare .
7 1 Mean OT for box (x100). 0-244
8 2 # of observations with OT above extreme event threshold 0-32767
9-10 4 Spare .

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