SDI Operator's Manual
Version 2005
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GVAR
System Overview
GVAR (GOES
VARiable) is the data transmission format used with the current generation
of GOES meteorological satellites, beginning with GOES-8.
Unlike the evolutionary format of the former GOES system (GOES A superseded
by GOES AAA), the GVAR format is not compatible with the previous GOES AAA
format.
The purpose
of this appendix is to provide sufficient information about the GOES satellite
capabilities and the GVAR format for you to understand the data ingesting and
processing requirements.
The variable
scan length is a major difference between GVAR and GOES. Another difference
is that GOES operated in either the imager or sounder mode, whereas GVAR can
operate in both modes simultaneously. In fact, the GVAR sensor groups can scan
unrelated areas of the earth at the same time.
Table A-1.
GVAR Format
DOC |
IR1 |
IR2 |
VIS 1 |
VIS 2 |
VIS 3 |
VIS 4 |
VIS 5 |
VIS 6 |
VIS 7 |
VIS 8 |
SAD |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
|
| Each GVAR block has: |
10032-bit synchronization code |
| |
720-bit header |
| |
N-bit information field |
| |
16-bit CRC |
|
| Blocks
0 and 11 have a fixed length information field of 64,320 bits |
| Blocks
1 through 10 have variable length information fields directly dependent
on the scan width, with a minimum information field length of 21440 bits |
| A single
imager scan generates blocks 0-10 in sequence |
| Blocks
0 through 10 may be followed by any number of block 11s (0-N) depending
on what is available. In priority order, the next block(s) transmitted
will be: |
1 |
Next
Imager Scan - blocks 0-10 |
2 |
Imager
Compensation and Servo Errors - 1 block 11 |
3 |
Sounder
Compensation and Servo Errors - 1 block 11 |
4 |
Imager
Telemetry Statistics - l block 11 |
5 |
Imager
Spacelook Statistics and Data - 2 block 11s |
6 |
Imager
Calibration Coefficients and Limits - 1 block 11 |
7 |
Imager
ECAL Statistics and Data - 2 block 11s |
8 |
Imager
Blackbody Statistics and Data - 1 block 11 |
9 |
Imager
Visible NLUIS - 2 block 11s |
10 |
Imager
Star Sense Data - 9 block 11s |
11 |
Sounder
Scan Data - 2 to 400 block 11s |
12 |
Sounder
Telemetry Statistics - 1 block 11 |
13 |
Sounder
Spacelook Statistics and Data - 5 block 11s |
14 |
Sounder
Calibration Coefficients and Limits - 2 block 11s |
15 |
Sounder
ECAL Statistics and Data - 3 block 11s |
16 |
Sounder
Blackbody Statistics and Data - 5 block 11s |
17 |
Sounder
Visible NLUTS - 9 block 11s |
18 |
Sounder
Star Sense Data - 3 block 11s |
19 |
GIMTACS
Text Messages - 1 to 2 block 11s |
20 |
SPS
Text Messages - 1 block 11 |
21 |
Auxiliary
Data - 1 to N block 11s |
22 |
Fill
Data - 1 block 11 |
|
The GVAR format
has its origin in the Operational VAS Mode AAA (Triple A) format. The AAA format
consists of a repeating sequence of twelve fixed-length, equal size blocks.
The range and
flexibility of satellite operations has increased with the advent of the three-axis
stabilized GOES craft employing two independent instruments, each having
two-degree of freedom scanning mirrors. Using a fixed length transmission format
would have placed operational limitations on the satellite's capabilities.
The GVAR format was developed to permit full use of the new capabilities while
maintaining as much commonality with AAA reception equipment as possible.
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