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Electronic cross-talk (Bands 5 - 7, 20 - 26)

Description

Analyses of pre-launch test data showed that radiometric errors equal to 10% or more had been present in the SWIR bands (Bands 5, 6, 7 and 26), and 5% or more in the MWIR bands (Bands 20 - 25).

All 500 m bands are sampled twice (in scan direction) for each instance that the 1000 m bands are sampled, and these are identified as sub-frame 1 and sub-frame 2. For SWIR Bands 5, 6 and 7, there are differences in radiometric performance between the two sub-frames that we believe to be primarily due to the presence of electronic cross-talk.

Impact to L1B Data Set

This effect exists for all L1B products produced using software Version 3.0 and lower and amounts to radiometric errors of up to 10% in the SWIR bands (5, 6, 7, 26) and 5% in the MWIR bands (20 – 25).

Estimated Impact to L2 Science Products

This effect exists for all L1B products produced using software Version 3.0 and lower and is associated with errors greater than 2% in the SWIR bands and greater than 1% (0.75% fo band 20) for the MWIR bands.

Cause of Effect

These errors are due to electronic cross-talk while viewing structured Earth scenes, and were not evident in the low contrast scenes used for calibration. Electronic cross-talk is believed to be related to incomplete restoration of the baseline voltage on the capacitor used for signal integration in the FPA electronics. This effect was reduced by means of a change in the electronics external to the FPA prior to launch, but the system was not re-tested between this electronics change and launch.

Mitigation Approach/ Added Testing to Characterize Effect

Early MODIS data indicated that the electronics change reduced the errors from electronic cross-talk, but did not eliminate the effects. Subsequent on-orbit testing indicated that changing the detector bias voltage would reduce this cross-talk effect. For bias voltages larger than the –1.1 V used at launch, these changes led some detectors into reverse bias operation. Beginning in November 2000, a bias voltage level was found that minimized the electronic cross-talk and allowed all detectors to operate in reverse bias. Quantitative results for the magnitude of this effect are not available at the present time.

The reflective LUTs V2.4.4.2 contain a B-side SWIR OOB (5.3 micron leak) correction to improve the calibration of the firsrt subsample (in bands 5, 6, 7) and for band 26. The reflective LUTs V2.5.4.0 incorporate a new SWIR OOB correction. In both cases, the correction switch is On for the B-side calibration, OFF for the A-side. The SWIR OOB correction switch had previously been turned OFF for SWIR bands in LUT V2.4.3.1.

Estimated Schedule to Complete

Using SRCA tests, the magnitude of this effect was evaluated for the period after November 1, 2000. The analysis review is scheduled to be completed by October 31, 2001.

History of Characteristic

Time-dependent table of Electronic cross-talk testing

UTC TimeYYYYDDD.HHMM Vdet,Itwk Calibration
2000055.1527 190,79  
2000055.2004 sweep on No
2000055.204 190,79  
2000057.1616 226110  
2000057.182 sweep on No
2000057.1839 226110  
2000058.1444 220110  
2000059.1348 226110  
2000059.1908 sweep on No
2000059.221 226110  
2000061.2112 220110  
2000064.132 224110  
2000065.1913 228110  
2000066.1712 226110  
2000075.0059 sweep on No
2000075.011 225  
2000075.0137 sweep on  
2000075.0148 224  
2000075.0236 sweep on No
2000075.0248 223  
2000075.0323 sweep on No
2000075.0334 222  
2000075.0414 sweep on No
2000075.0425 221  
2000075.0528 sweep on No
2000075.054 220  
2000075.0619 sweep on No
2000075.0631 219  
2000075.071 sweep on No
2000075.0722 218  
2000075.0847 sweep on No
2000075.0859 226110  
2000083.144 218100  
2000084.1758 226110  
2000173.1842 190,79  
2000173.2242 226110  
2000174.0018 218100  
2000174.0425 226110  
2000221.16 190,79  
2000232.2049 226110  
2000238.1325 Sweep on No
2000238.134 226110  
2000238.1412 Sweep on No
2000238.1421 226110  
2000238.1504 Sweep on No
2000238.1523 226110  
2000252.1337 110,79  
2000252.1612 226110  
2000256.1412 110,79  
2000256.1639 226110  
2000291.1533 110,79  
2000291.1727 226110  
2000292.1943 110,79  
2000294.1329 226110  
2000305.1912 110,79  
2001113.2047 Sweep on No
2001113.2058 185,79  
2001152.1507 Sweep on No
2001152.1515 185,79  
2001183.2248 190,79  
2001214.0022 110,79  
2001214.0111 190,79  
2001221.2018 110,79  
2001221.211 190,79