McIDAS Programmer's Manual
Version 2003

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GVAR Sounder

GVAR Sounder areas are decoded from Block 11 data. The GVAR Sounder decoder reads the Block 11 holding areas, which contain blocks of type 32 (20 hex), type 35 (23 hex) and others. These blocks are documented in OGE, sections 3.3.7.2 and 3.3.7.3.

Navigation and calibration data is read from type 32 blocks, which are sounder documentation blocks. Sensor data is read from type 35 blocks, which are sounder scan data blocks. After the sensor data is read, it is reformatted and placed in the sounder image area.

 

The band information for the GVAR Sounder is provided in Appendix B, Satellite Information.

GVAR Sounder directory block

Word Value Description

12

10

line resolution; if lines are sampled or averaged, the resolution is a multiple of 10

13

10

element resolution; if pixels are sampled or averaged, the resolution is in multiples of 10

14

19

number of bands

19

524287

band filter map; translates to 0007ffff hex; a bit is set for each of bands 1 - 19

25-32

Priority Completed

normal entry; ASCII

49

36 or
216

length of the data block line prefix documentation, in bytes;
if 216, the first 180 words of Sounder Auxiliary Data block have been have been added

50

0

length of the data block line prefix calibration, in bytes

51

up to 24
(in multiples of four)

length of the data block line prefix band list, in bytes; see the section below for more information

52

GVAR

image source type; 4 bytes ASCII

53

RAW

calibration type; 4 bytes ASCII

GVAR Sounder data block

The GVAR Sounder produces data for a given spatial location in 18 IR spectral bands and one visible band. The number of bands in the sounder data must match the value in word 14 of the directory block. Word 19 designates the band map. All sounder data fields are 13 bits placed in 2-byte (16-bit) fields. Each data point in a scan data block has 23 bands of data. The data points correspond to a geographic area 11 pixels west-east and 4 pixels north-south. For each image line, the decoder produces 11 sets of 23 interleaved fields of data.

Bands 20-23 of this data are not displayable; they hold the latitude and longitude of the first 19 bands. The latitude and longitudes are 32-bit values. Since the actual sounder data is 16 bits, the latitude and longitude values must be split in half to store them in the area structure.

Band 20 holds the two most significant bytes of the latitude; band 21 holds the two least significant bytes. Band 22 holds the two most significant bytes of the longitude; band 23 holds the two least significant bytes.

If the latitude and longitude values are not requested, the band list section will contain 20 bytes total with 19 bytes used.

These latitude and longitude values are in the Gould floating point format. See OGE, section 3.5.4. For example, if the latitude of a data point is 100.1640625, the hex representation is 42642A00; band 20 holds 4264, and band 21 holds 2A00.

This package does not provide any code for using these latitudes and longitudes; they are included only for reference purposes.

The four sounder detectors are numbered 1, 2, 3, and 4. Each data block line contains information from only one detector. The documentation block contains a field indicating which detector was used for the current line.

The line prefix contains a 4-byte validity code and a documentation region, which is described in the table below. The remainder of the line consists of the interleaved sounder data.

Documentation region Bytes OGE table

first nine words of the Sounder Auxiliary Data Block ID

9

3-8

year, day and time of the scan line start

8

3-11

scan status

2

3-11

number of blocks in the scan

2

3-11

O&A location (not used)

2

 

detector status

10

3-11

number of the detector used for this line

1

 

padding

2

 

If the value in word 49 of the area directory is 216, the first 180 words of the Sounder Auxiliary Data block have been inserted here.

180

3-11

GVAR Sounder navigation block

Navigation blocks contain 640 words. Unless otherwise noted, words are twos complement binary integers. Navigation information comes from Block 11 records, type 32. Bytes designated R*4 in the OGE Tables are in Gould format in the holding areas. They must be scaled and then converted to integer, or converted to Real on the machine doing the decoding, scaled as designated below, and then converted to integer.

If the latitude and longitude values are not requested, the band list section will contain 20 bytes total with 19 bytes used.

Because the word allocation information for the sounder navigation block is nearly identical to that for the imager, it is not repeated here. Only the words with a different description are shown below. That difference is usually the OGE table number and/or byte numbers.

Word Value Description

3

 

scan status; bits 0-15 are right justified, bit 15 is the least significant bit; the IMC active flag is bit 8, counting from the least significant bit; 1=active (OGE Table 3-11, bytes 31-32)

4

 

yaw-flip flag; bits 0-15 are right justified, bit 15 is the least significant bit; the yaw-flip processing enabled flag is bit 16, counting from the least significant bit; 1=enabled (OGE Table 3-10, bytes 57-58)

6 - 62

 

(OGE Table 3-11, bytes 323 - 550)

63 - 117

 

roll attitude angle (OGE Table 3-11, bytes 551-770)

130-184

 

repeat of Words 63-117 for pitch attitude angle (OGE Table 3-11, bytes 771-990)

185-239

 

repeat of Words 63-117 for yaw attitude angle (OGE Table 3-11, bytes 991-1210)

258-312

 

repeat of Words 63-117 for roll misalignment angle (OGE Table 3-11, bytes 1211-1430)

313-367

 

repeat of Words 63-117 for pitch misalignment angle (OGE Table 3-11, bytes 1431-1650)

370

 

imager/sounder instrument flag; 1=imager, 2=sounder

380

 

instrument nadir, north/south cycles (OGE Table 3-6, byte 3005)

381

 

instrument nadir, east/west cycles (OGE Table 3-6, byte 3006)

382

 

instrument nadir, north/south increments (OGE Table 3-6, bytes 3007-3008)

383

 

instrument nadir, east/west increments (OGE Table 3-6, bytes 3009-3010)

GVAR Sounder calibration block

Word Value Description

1 - 4

 

visible bias coefficients; one per detector (OGE Table 3-11, bytes 3075-3090)

5 - 8

 

visible first order gain coefficients; one per detector (OGE Table 3-11, bytes 3091-3106)

9 - 12

 

visible second order gain coefficients; one per detector (OGE Table 3-11, bytes 3107-3122)

13

 

visible radiance to albedo conversion factor (OGE Table 3-11, bytes 3123-3126)

14 - 31

 

IR bias scaling factors; one per IR channel (OGE Table 3-11, bytes 3991-4278);
all channels contain the same values for each detector

32 - 49

 

IR gain scaling factors; one per IR channel (OGE Table 3-11, bytes 4279-4566);
all channels contain the same values for each detector

50-128

0

 


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