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 These satellites are designated GOES I-M. Unlike the evolutionary format of the former GOES system (GOES A superseded by GOES AAA), the GVAR format is not compatible with the previous GOES AAA format.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

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.