NOAA KLM User's Guide

Section 9.2.2

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9.2.2 Mapped GAC (Mercator) Product

The mapped GAC (Mercator) data are organized as visible (Channel 1), and daytime and nighttime IR (Channel 4). These data are reported in pairs of files, totaling six files. The first file of each file pair consists of a documentation record for that variable, immediately followed by an EOF and a second file containing the data records for the same variable. All records are 4,052 bytes in length. Both documentation and data records are in binary format and have the same length. A value of zero indicates missing data.

Every day a 3480 cartridge is created which contains a day's worth of mapped GAC data in the mercator projection. Table 9.2.2-1 contains the general file structure of the daily mercator KLM Master Map cartridge. Each cartridge contains 6 files arranged as shown in the table.

The format of the basic documentation record is the same as the polar stereographic KLM Master Map which is contained in Table 9.2.1-2.

Each data record (4,052 bytes) consists of one mapped row, containing 4052 pixels of data. Each pixel is represented by one byte of data.

Table 9.2.2-1. General structure of the mercator KLM Master Map cartridge.
File, record # Contents
Visible Channels
F1, rec. 1 Channel 1 documentation record. See Table 9.2.1-2 for format.
F2, rec. 1-984 Channel 1 data records. Consists of 4,052 bytes of data or 1 mapped row of data. Each row contains 4052 pixels of data. Each pixel is one byte. A value of 0 indicates missing data.
IR Channels (Daytime)
F3, rec. 1 Channel 4 documentation record. See Table 9.2.1-2 for format.
F4, rec. 1-984 Channel 4 data records. Same as F2 data records
IR Channels (Nighttime)
F5, rec. 1 Channel 4 documentation record. See Table 9.2.1-2 for format
F6, rec. 1-984 Channel 4 data records. Same as F2 data records.


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