McIDAS Programmer's Manual
Version 2003

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GVAR Imager

The GVAR Imager provides two types of data:

The supplemental data is provided in Block 0, which is the GVAR Imager documentation block. Block 0 has its own directory block, validity code, documentation region and data. The GVAR Imager sensor data likewise has its own directory, data, navigation and calibration blocks. Both types of data are described below.

The OGE tables referenced in this section are from Operations Ground Equipment, Internal Specification, DRL 504-02-1 Part 1, Specification No E007020, released February 9, 1994, Space Systems/Loral, 3825 Fabian Way, Palo Alto, California 94303-4604. That document describes data which is formatted by the ground station and then retransmitted.

 

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

Block 0

The GVAR Imager documentation, Block 0, contains additional control information about an image. Some of this information is also contained in the imager sensor data. For each line of GVAR Imager sensor data transmitted, one line of Block 0 documentation is transmitted and stored in a separate area. Below are the values specific to the Block 0 directory.

Word Value Description

12

8

line resolution

13

1

element resolution

14

1

number of bands

19

1

band map

25 - 32

RT IMGR DOC

normal entry; ASCII

49

44

length of the data block line prefix documentation,
in bytes

50

0

length of the data block line prefix calibration,
in bytes

51

0

length of the data block line prefix band list, in bytes

52

GVAR

image source type; 4 bytes ASCII

53

RAW

calibration type; 4 bytes ASCII

The line prefix's validity code for Block 0 is four bytes. Its documentation region is 44 bytes, consisting of the following:

Documentation region Bytes OGE table

block header CRC

2

3-5

scan status

4

3-6

year, day and time from Block 0

8

3-6

block header

30

3-5

The rest of the Block 0 line contains 8040 bytes of 8-bit data. See OGE Table 3-6.

Bytes 17-24 contain the time the block was sent from the ground station.

GVAR Imager directory block

The GOES-8 through GOES-12 satellites have two instruments: an imager and a sounder. Areas with SSEC-assigned, even-numbered sensor sources provide imager data, while odd-numbered sensor sources provide sounder data. Word 52 of the directory block contains the image source type (GVAR) for 2-byte GVAR data as it is ingested. Word 53 contains the units that data is stored in; RAW for 2-byte raw GVAR data.

Word 14 of the directory block contains the number of spectral bands present in an image. The filter band map in word 19 of the directory block describes the bands in an area. A bit is set for each band appearing in the area. The number of bands must match the value in word 14. The values specific to the sensor data's directory block are shown below.

Word Value Description

11

2

number of bytes per band

19

1 for VIS
2, 4, 8 or 16 for IR

band map; one bit should be set for each band in the area

25 - 32

RT IMGR IR
RT IMGR VIS
RT IMGR

normal entry; ASCII
visible band
multibanded

49

226

length of the data block line prefix documentation if single band, otherwise a higher value; in bytes

50

0

length of the data block line prefix calibration,
in bytes

51

0

length of the data block line prefix band list,
in bytes

52

GVAR

image source type; 4 bytes ASCII

53

RAW

calibration type; 4 bytes ASCII

55

1

 

GVAR Imager data block

The GVAR Imager produces observational data for a spatial location in five spectral bands: one visible (VIS) and four infrared (IR). An image contains only one of these five bands. Word 19 in the directory block contains a band filter map indicating the area file's band.

The highest resolution for a visible image is one. It is four for an IR image, since longer wavelengths have less resolution. For a GVAR satellite, resolution one means approximately 1 km resolution at the satellite subpoint.

Each element in a GOES-8 image contains one 10-bit pixel representing raw data from the instrument. Each pixel is stored as two bytes in the McIDAS-X area file. The hardware shifts the data so the 10 bits are formatted as shown below. The x's are the data bits; the rest is 0-filled after shifting.

| 0 | x | x | x | x | x | x | x | x | x | x | 0 | 0 | 0 | 0 | 0 |

The sensor data's line prefix contains a 4-byte validity code and a 76-byte documentation region consisting of the following:

Documentation region Bytes OGE table

block header CRC (the last three bits only); a bit is set if the block header copy is good; this data is usually 00,07

2

 

scan status

4

3-6

year, day and time from Block 0

8

 

block header

30

3-5

line documentation consisting of sixteen pairs of 10-bit fields, right justified; each 10-bit field can be obtained with a LOGICAL AND against 03FF

32

3-7

block zero record, first 150 words

150

3-6

The block header and line documentation blocks are included for every band in the image line.

The rest of the line consists of up to 41920 bytes of data. Since it is 2-byte data, half that many pixels are represented.

Bytes 17-24 contain the time the block was sent from the ground station.

GVAR Imager navigation block

The GVAR Imager navigation block contains 640 words. Unless otherwise noted, words are twos-complement binary integers. This navigation information comes from Block 0 records. Bytes designated R*4 in OGE Tables are in Gould format. They must be scaled and converted to integers or converted to Real on the machine doing the decoding, scaled as designated below, and then converted to integer.

Word Value Description

1

GVAR

navigation type; 4 bytes ASCII

2

 

ASCII string, usually a letter followed by three integers

3

 

imager scan status; bits 0-15 are right justified, with 15 the least significant; IMC active flag is bit 8, counting from the least significant bit; 1=active; see OGE Table 3-6, bytes 3-6

4

 

imager scan status; bits 16-31 are right justified, with 31 the least significant; yaw-flip processing enabled flag is bit 16, counting from the least significant bit; 1=enabled; see OGE Table 3-6, bytes 3-6

5

0

reserved

6 - 62
6
7
8
9
10
11
12
13 - 14
15
16
17
18
19 - 31
32 - 42
43 - 51
52 - 60
61
62

 

see OGE Table 3-6, bytes 295 - 522
reference longitude, rad*10000000
reference distance from nominal, km*10000000
reference latitude, rad*10000000
reference yaw, rad*10000000
reference attitude roll, rad*10000000
reference attitude pitch, rad*10000000
reference attitude yaw, rad*10000000
epoch date/time, BCD format
delta from epoch time, minutes*100
image motion compensation roll, rad*10000000
image motion compensation pitch, rad*10000000
image motion compensation yaw, rad*10000000
longitude delta from reference values, rad*10000000
radial distance delta from reference values, km*10000000
sine of the geocentric latitude delta values, units*10000000
sine of the orbit yaw delta values, units*10000000
daily solar rate, rad/min*10000000
exponential start time from epoch, minutes*100

63 - 117
63
64
65
66
67
68
...
95
96
97
98
99
100
101
102
103-107
108-112
113-117
118-127
128
129





















MORE
GVAR

roll attitude angle (OGE Table 3-6, bytes 523-742)
exponential magnitude, rad*10000000
exponential time constant, minutes*100
mean attitude angle, rad*10000000
number of sinusoids/angles, no units
magnitude of first order sinusoid, rad*10000000
phase angle of first order sinusoid, rad*10000000
...
magnitude of fifteenth sinusoid, rad*10000000
phase angle of fifteenth sinusoid, rad*10000000
number of monomial sinusoid, no units
order of applicable sinusoid, no units
order of first monomial sinusoid, no units
magnitude of monomial sinusoid, rad*10000000
phase angle of monomial sinusoid, rad*10000000
angle from epoch at daily solar rate, rad*10000000
repeat of words 98-102 for second monomial
repeat of words 98-102 for third monomial
repeat of words 98-102 for fourth monomial
reserved
4 bytes ASCII
4 bytes ASCII

130-239
130-184
185-239
240-255
256
257





MORE
GVAR

attitude angles
repeat of Words 63-117 for pitch attitude angle; see OGE Table 3-6, bytes 743-962
repeat of Words 63-117 for yaw attitude angle; see OGE Table 3-6, bytes 963-1182
reserved
4 bytes ASCII
4 bytes ASCII

258-367
258-312
313-367

 

misalignment angles
repeat of Words 63-117 for roll misalignment angle; see OGE Table 3-6, bytes 1183-1402
repeat of Words 63-117 for pitch misalignment angle; see OGE Table 3-6, bytes 1403-1622

368

 

year and Julian day, yyyddd

369

 

nominal start time of the image; comes from Block 0 when navigation data is taken from Block 0, HHMMSSmmm

370

1

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

371-379

 

reserved

380

 

instrument nadir, north/south cycles; see OGE Table 3-6, byte 6305

381

 

instrument nadir, east/west cycles; see OGE Table 3-6, byte 6306

382

 

instrument nadir, north/south increments; see OGE Table 3-6, byte 6307-6308

383

 

instrument nadir, east/west increments; see OGE Table 3-6, byte 6309-6310

384

MORE

4 bytes ASCII

385

GVAR

4 bytes ASCII

386-511

 

reserved

512

MORE

4 bytes ASCII

513

GVAR

4 bytes ASCII

514-640

 

reserved

GVAR Imager calibration block

The imager calibration block is made up of 128 words (512 bytes), as shown in the table below. The data is in the Gould format.

Word Value Description

1 - 8

 

visible bias coefficients; one per detector (OGE Table 3-6, bytes 6399-6430)

9 - 16

 

visible first order gain coefficients; one per detector (OGE Table 3-6, bytes 6431-6462)

17 - 24

 

visible second order gain coefficients; one per detector (OGE Table 3-6, bytes 6463-6494)

25

 

visible radiance to albedo conversion factor (OGE Table 3-6, bytes 6495-6498)

26 - 29

 

det side 1 IR bias scaling factors; one per IR channel (OGE Table 3-6: bytes 6667-6670 Ch 4, Side 1; bytes 6675-6679 Ch 5, Side 1; bytes 6683-6686 Ch 2, Side 1; bytes 6691-6694 Ch 3, Side 1)

30 - 33

 

det side 2 IR bias scaling factors; one per IR channel (OGE Table 3-6: bytes 6695-6698 Ch 4, Side 2; bytes 6703-6706 Ch 5, Side 2; bytes 6711-6714 Ch 2, Side 2; bytes 6719-6722 Ch 3, Side 2)

34 - 37

 

det side 1 IR gain scaling factors; one per IR channel (OGE Table 3-6: bytes 6723-6726 Ch 4, Side 1; bytes 6731-6734 Ch 5, Side 1; bytes 6739-6742 Ch 2, Side 1; bytes 6747-6750 Ch 3, Side 1)

38 - 41

 

det side 2 IR gain scaling factors; one per IR channel (OGE Table 3-6: bytes 6751-6753 Ch 4, Side 2; bytes 6759-6762 Ch 5, Side 2;bytes 6767-6770 Ch 2, Side 2; bytes 6775-6778 Ch 3, Side 2)

42-128

0

 

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