Revised 3/6/01

For GOES-12 and -N, the selection of infrared channels on the GOES Imagers will be different from that currently on GOES-8 through -11. Users will probably need to modify their GVAR ingest software to accommodate this change. The current 12-µm channel (channel 5), which has two 4-km detectors, will be replaced by a 13.3-µm channel with one 8-km detector. The current 6.7-µm channel (channel 3), which has one 8-km detector, will have two 4-km detectors, and its spectral response will be shifted slightly and broadened, giving it a nominal center wavelength near 6.5 µm. The visible channel (channel 1) will be unchanged.

The current GOES-8 through -11 detector configuration is as follows:

 The GOES-12 and -N detector configuration will be as follows:

To keep the channel numbering system consistent among satellites, NOAA will always maintain the same association between channel number and wavelength. Also, NOAA will number the channels in order of increasing wavelength. The new 13.3-µm channel will be labeled channel 6 to distinguish it from the old 12-µm channel (channel 5). (But since we assume the old 6.7-µm and the new 6.5-µm channels are effectively the same, both are channel 3.)

Beginning with GOES-O, another change will be made--channel 6 will have two 4-km detectors instead of one 8-km detector. The configuration will be as follows:

The observations in the infrared channels of the imagers are sent to users in blocks 1 and 2 of the GOES VARiable data stream (GVAR). For GOES-8 through GOES-11, the GVAR does not order the channels according to increasing wavelength, but by the arbitrary system, 4, 5, 2, 3. (This ordering was based on the old pre-GOES-8 AAA data stream). Beginning with GOES-12, this will be changed. The data in GVAR will be in order of increasing channel wavelength. For example, for GOES-12 the order will be 2, 3, 4, 6.

The new ordering will apply only to the GVAR for GOES-12 and beyond. The original GVAR ordering will be maintained for GOES-8 through GOES-11 throughout their lifetimes on orbit.

More information on these GVAR changes may be found in the following (slightly updated) excerpt from the GVAR Requirements Document:

Updated Excerpt from "Requirements for SPS, GVAR, and PM Modifications to Accommodate Imager Channel Changes for GOES-12 and Beyond" (Michael Weinreb, 3/16/99)

1. Channel Numbering: For all satellites from GOES-8 through GOES-P, the channel numbering will be fixed as a function of wavelength, as follows:

No imager will have both channels 5 and 6. Those on GOES-8 through GOES-L have channel 5. Those on GOES-12 through -O will have channel 6. For GOES-P, it is TBD.

This numbering system will be incorporated in the index LICHA, which is word 5 of the line documentation segment of each record of GVAR blocks 1 and 2.

2. Order of Data Records in GVAR: The order of the assignment of channels to the records in blocks 1 and 2 of GVAR will be changed, beginning with GOES-12. For GOES 8 through GOES-L, it is

Block 1 (four IR records)

Block 2 (three IR records)

The terms "North" and "South" detectors refer to the Earth frame of reference.

For GOES-12 and beyond, the records will be ordered with increasing wavelength. For GOES-12 and -N the order will become

Block 1 (four IR records)

 Block 2 (three IR records)

 
And for GOES-O and -P it will become

Block 1 (four IR records)

Block 2 (four IR records)

(If the GOES-P Imager returns to the 12-µm channel in place of the 13.3-µm channel, then the last two records in block 2 will carry data for channel 5 instead of 6.)

The word LICHA in each record’s line documentation segment indicates the channel number.

3. Imager Factory Coefficients in GVAR: Beginning with GOES-O, the imagers will have an additional infrared detector. There will be eight, instead of seven, IR detectors. In block 0, the amount of space for the drift correction coefficients (currently words 5587-6304) will need to be increased by approximately 15% to accommodate the data for the eighth detector. To make room in block 0, the factory coefficients (currently words 6305-8040) will be removed and will be sent instead in a new type of block 11. [The reason we retain the drift correction data but not the factory data in block 0 is that the drift correction data are updated with each scan line, whereas the factory coefficients remain the same for a given satellite for all time. (And, of course, blocks 0 are sent with each scan line, whereas blocks 11 are sent less often.)]

The following was added in March 2001: The new "Imager Factory Coefficients" block 11 will be introduced early with the GOES-12 satellite. This block 11 will be identified by the value "20" in words 5 and 6 ("Product ID") of the GVAR block header. However, the changes to block 0, including the removal of the Imager factory data and the addition of drift correction data for the eighth IR detector, will not become effective until GOES-O.

4. Versions of GVAR: The changes to GVAR outlined above will become effective with the GOES-12 satellite but will not be retroactive to GOES-8 through GOES-11.

The following was added in March 2001: Users can identify the version of GVAR they receive from word 8 ("Version Number") of the GVAR block header. When this word has the value "0," it indicates the original (GOES-8 through GOES-11) version of GVAR. The value "1" will also indicate the GOES-8 through -11 version of GVAR, but with certain spare words now utilized to transmit the status of a new algorithm to mitigate certain calibration anomalies that occur near satellite midnight. NOAA expects to make version 1 operational in mid- to late-2001. Its receipt will not require any modifications or actions by current users. For the GVAR versions for GOES-12/N and GOES-O/P, word 8 of the GVAR block header will take the values "2" and "3," respectively.