SDI Operator's Manual
Revised July 2000

[Search Manual] [Table of Contents] [FAQ] [Go to Previous] [Go to Next]

GVAR System Overview

GVAR (GOES VARiable) is the data transmission format used with the new generation of GOES meteorological satellites. These satellites are designated GOES I-M. Unlike the evolutionary format of the former GOES system (GOES A superseded by GOES AAA), the GVAR format is not compatible with the previous GOES AAA format.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 GVAR format greatly impacts the data ingest hardware.

The purpose of this appendix is to provide sufficient information about the GOES I-M 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 I-M 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.

[Search Manual] [Table of Contents] [FAQ] [Go to Previous] [Go to Next]