SDI Operator's Manual
Version 2005

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Scan Format

The GVAR transmission sequence is depicted in Table A-1. It consists of twelve blocks numbered 0 through 11. Blocks 0 through 10 are transmitted when an Imager scan line is completed. Block 10 is followed by a variable number of block 11s (0-N) according to the data available for transmission. Block 11 (Sounder/Auxiliary Data-SAD) transmits sounder data and all non-imager data. Blocks 1 through 10 vary in length directly in accordance with the length of the imaging instrument scan line. Table A-2 provides further details about the structure of the GVAR format. In turn, Tables A-3 through A-7 further explain the GVAR block formats.

 

Table A-2. GVAR Scan Characteristics

Scan Characteristics  
Period Variable
Blocks/Imager Scan 11
Bit Rate   2,111,360 bits/second
   
Block Characteristics  
Period 15.25 to 104.6 msec
Sync Length 10032 bits
Header Word Length 8 bits/word
Header Length (triple redundant) 90 words (720 bits)
   
Information Field:  
  Block 0 - Documentation Block (Table A-3)
  Word Size 8 bits
  Field Length 8040 words (64,320 bits)
   
  Block 1 - Infrared Block 1 (Table A-4)
  Word Size 10 bits
  Field Length 68 to 21008 words*
  Number of Records 4 per block
  Line Documentation 16 words
  IR Detector Data 1 to 5236 words
   
  Block 2 - Infrared Block 2 (Table A-5)
  Word Size 10 bits
  Field Length 51 to 15756 words*
  Number of Records 3 per block
  Line Documentation 16 words
  IR Detector Data 1 to 5236 words
   
  Blocks 3 to 10 - Visible Blocks (Table A-6)
  Word Size 10 bits
  Field Length 20 to 20960 words*
  Number of Records 1 per block
  Line Documentation 16 words
  Visible Detector Data 4 to 20944 words
   
  Block 11 - Sounder Auxiliary Data (Table A-7)
  Word Size 6, 8 or 10 bits
  Field Length 10720, 8040 or 6432 words
  Record Types 1 to 8
     
  Cyclic Redundancy Check (CRC) 16 bits
 
* Variable length information fields are subjected to zero packing to meet the minimum block length of 32208 bits. The maximum values above assume a 19.2 degree scan width.

 

Table A-3. GVAR Block 0 (Documentation Block) Format

Sync Code
1254 Bytes
Header
90 Bytes
Triple Redundant
Information Field - 8,040 Bytes

CRCC
2 Bytes

Instrument and Scan Status Orbit and Attitude Parameters
1412 Bytes
Scan Reference Data
616 Bytes
Grid Data
3080 Bytes
Spares
918 Bytes
Factory Parameters
1736 Bytes
10,032 Bits 720 Bits 2,224 Bits 11,296 Bits 4,928 Bits 24,640 Bits 7,344 Bits 13,888 Bits 16 Bits

Note: Block 0 provides documentation for blocks 1-10 (imager data blocks) only. It does not apply to Block 11.

 

Table A-4. GVAR Block 1 (IR1 Block) Format

Sync Code
1254 Bytes
Header
90 Bytes
Triple Redundant
Data Field - Maximum 15,756 Words (10-bit)
CRCC
2 Bytes
Channel 4, Detector 1
Channel 4, Detector 2
Channel 5, Detector 2

Line Doc.

16 Words

Data *

1-5,236 Words

Line Doc.

16 Words

Data *

1-5,236 Words

Line Doc.

16 Words

Data *

1-5,236 Words

10032 Bits 720 Bits 160 Bits 10-52,360 Bits 160 Bits 10-52,360 Bits 160 Bits 10-52,360 Bits 16 Bits

* The minimum Data Field is specified at 21,440 bits (2,1440 words). Therefore, the minimum detector field length, including the 160-bit Line Doc, is 715 words. Detector data fields less than 715 words are padded out to 715 words with zeros.

 

Table A-5. GVAR Block 2 (IR2 Block) Format

Sync Code
1254 Bytes
Header
90 Bytes
Triple Redundant
Data Field - Maximum 15,756 Words (10-bit)
CRCC
2 Bytes
Channel 2, Detector 1
Channel 2, Detector 2
Channel 3

Line Doc.

16 Words

Data *

1-5,236 Words

Line Doc.

16 Words

Data *

1-5,236 Words

Line Doc.

16 Words

Data *

1-5,236 Words

10032 Bits 720 Bits 160 Bits 10-52,360 Bits 160 Bits 10-52,360 Bits 160 Bits 10-52,360 Bits 16 Bits

* The minimum Data Field is specified at 21,440 bits (2,1440 words). Therefore, the minimum detector field length, including the 160-bit Line Doc, is 715 words. Detector data fields less than 715 words are padded out to 715 words with zeros.

 

Table A-6. GVAR Blocks 3-10 (Visible Image Data) Format

Sync Code
1254 Bytes
Header
90 Bytes
Triple Redundant
Data Field - Variable Length - 2,144-20,960 Words (10-bit)
CRCC
2 Bytes

Line Doc.

16 Words

Data

4-20,944 Words

Zeros *

0-2,124 Words

10032 Bits 720 Bits 160 Bits 40-209,440 Bits 0-21,240 Zero Bits 16 Bits

* The minimum Data Field is specified at 21,440 bits (2,1440 words). Therefore, blocks having less than 2,128 data words (21,280 bits) are padded with zeros to achieve the minimum Data Field length.

 

Table A-7. GVAR Block 11 Format for Sounder Scan Data

Sync Code
1254 Bytes
Header
90 Bytes
Triple Redundant
Data Field - Variable Length - 64,320 Bits (6-, 8- or 10-bit Words)
CRCC
2 Bytes

SAD
Block ID

40 6-bit Words

Data - 64,080 Bits

Twelve blocks of raw data samples consisting of one sample from each of 76 sensors.

Line and pixel locators

Seventy-six (76) calibrated channels of 12 pixels each

10032 Bits 720 Bits 240 Bits 4,096 Bits/Block
49,152 Bits Total
336 Bits 16 Bits/Pixel
14,592 Bits Total
16 Bits

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