Sorry, you need to enable JavaScript to visit this website.

MCST Banner Image

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 Time
YYYYDDD.HHMM
Vdet,ItwkCalibration
2000055.1527190,79 
2000055.2004sweep onNo
2000055.204190,79 
2000057.1616226110 
2000057.182sweep onNo
2000057.1839226110 
2000058.1444220110 
2000059.1348226110 
2000059.1908sweep onNo
2000059.221226110 
2000061.2112220110 
2000064.132224110 
2000065.1913228110 
2000066.1712226110 
2000075.0059sweep onNo
2000075.011225 
2000075.0137sweep on 
2000075.0148224 
2000075.0236sweep onNo
2000075.0248223 
2000075.0323sweep onNo
2000075.0334222 
2000075.0414sweep onNo
2000075.0425221 
2000075.0528sweep onNo
2000075.054220 
2000075.0619sweep onNo
2000075.0631219 
2000075.071sweep onNo
2000075.0722218 
2000075.0847sweep onNo
2000075.0859226110 
2000083.144218100 
2000084.1758226110 
2000173.1842190,79 
2000173.2242226110 
2000174.0018218100 
2000174.0425226110 
2000221.16190,79 
2000232.2049226110 
2000238.1325Sweep onNo
2000238.134226110 
2000238.1412Sweep onNo
2000238.1421226110 
2000238.1504Sweep onNo
2000238.1523226110 
2000252.1337110,79 
2000252.1612226110 
2000256.1412110,79 
2000256.1639226110 
2000291.1533110,79 
2000291.1727226110 
2000292.1943110,79 
2000294.1329226110 
2000305.1912110,79 
2001113.2047Sweep onNo
2001113.2058185,79 
2001152.1507Sweep onNo
2001152.1515185,79 
2001183.2248190,79 
2001214.0022110,79 
2001214.0111190,79 
2001221.2018110,79 
2001221.211190,79