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Time-dependent list of Non-functional or noisy detectors

 

Description

This characteristic is most significant for the SW/MWIR focal plane, which encompasses Bands 5 – 7, 26 and 20 – 25. The first four bands are the SWIR bands and the remaining six are the MWIR bands. RSB detectors are declared "noisy" based on the detector-dependent SNR. TEB detectors are declared "noisy" if the detector’s NEdT exceeds the specification for 2 weeks. These conditions are tracked by the Detector Quality Flags (DQF) in the Quality Assurance (QA) LUT.

Impact to L1B Data Set

Non-functional and noisy detectors are flagged to alert users. The L1B code does not calibrate EV pixels for non-functional detectors. Instead, the scaled integer is interpolated from the nearest live detectors.

Estimated Impact to L2 Science Products

The L1B product handles non-functional detectors in a manner to facilitate building images with L1B production data using simple raster scan software for the image generation. Science users should read and use the non-functional detector flags and decide for themselves the optimum manner to handle non-functional detector "gaps" for their products.

Cause of Effect

The MODIS SW/MWIR focal plane is designed to operate at reverse bias, and at launch was set to -1.1 volts. At launch all detectors were functional. All configurations before November 1, excluding the October 17 - 18 test period, are for an FPA bias larger than -1.1 V. This larger FPA bias, selected to minimize electronic crosstalk, forced several detectors into a forward bias condition that "turned off" these detectors.

Mitigation Approach/ Added Testing to Characterize Effect

Data for Non-functional detectors were replaced by nearest live-neighbor averages within the same scan in code version V2.4.3 (July 2000). The -1.3 V configuration used after October 31, 2000 results in reverse bias for all SW/MWIR detectors. Non-functional detectors are treated differently in Collection 6 processing (starting approximately May 2012). At that time, non-functional detectors will be given fill values that indicate the status of those detectors.

Estimated Schedule to Complete

The production of new tables is an on-going effort.

History of Characteristic

Terra Collection 6 (C6) processing began in August 2012.  For the remainder of 2012 and most of 2013, C6 and C5 processing will run concurrently.  The current Terra MODIS Collection 5 (V5) QA LUT, a time-dependent list of non-functional, noisy, and out-of-family detectors, as well as the collection 6 QA LUTs are available by clicking on the eponymous links below.  Information for processing based on earlier versions of the L1B code (collections 2, 3, and 4) is also available below.