McIDAS Programmer's Manual
Version 2015
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GVAR
Imager
The
GVAR Imager provides two types of data:
- Supplemental
data
- Sensor
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.
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 |
228 |
length, in bytes,
of the data block line prefix documentation if single band (last two bytes are zero); otherwise
a higher value |
50 |
0 |
length, in bytes,
of the data block line prefix calibration |
51 |
0 |
length, in bytes,
of the data block line prefix band list |
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
|
stray light correction status;
see OGE Table 3-6, bytes 259 - 260 |
2 |
3-6 |
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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