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Band 27 anomalous band width, anomalous gain

Description

The linear gain for Band 27 was observed to be changing on orbit in July 2000.

Impact to L1B data set

The radiance values for Band 27 were found to be inaccurate by an amount that increased nearly linearly over time from day 48 to day 162, 2000, reaching a 2.5% error.

Estimated impact to L2 science products

The brightness temperature effect is always less than 0.3K. Band 27 is used primarily for determining the cloud mask, but other bands could be used. If viewing large-scale spectral sructures such as atmospheric lines, investigatorsshould contact MCST to obtain the relative spectral response time dependence.

Cause of Effect

The short-wavelength side of the band pass filter is influenced by the dielectric coating on the window of the intermediate-stage of the radiative cooler. Beginning on day 48, the temperature of intermediate stage cooler window began to increase. This resulted in an increase the bandwidth, which in turn appeared as an increase in Band 27 gain in the Level 1B algorithm.

Mitigation Approach/ Added Testing to Characterize Effect

The Band 27 bandwidth has been more stable following the cooler outgas cycle in August 2000. A correction to bandwidth based on cooler window temperature is under consideration for installation into the L1B production algorithm.

Estimated Schedule to Complete

Completed.

History of Characteristic

Epoch
Number
Time SpanVersion Number at
start of epoch
General CharacteristicsImprovementsDocumentation
1Feb. 24, 2000 - June 28, 2000
2000055.1550 - 2000180.1900
2.3.2.0FPA temperature is controlled.Not applicable. 
2June 28, 2000 - July 12, 2000
2000180.1900 - 2000194.1440
2.4.2.0RSR changed as temperature control of FPA is lost. FPA floating full orbit.  
3July 12, 2000 - Aug. 3, 2000
2000194.1440 - 2000216.2004
2.4.2.0RSR changed as temperature control of FPA is lost. FPA floating full orbit.New B27 gains set.MCST Library M0915, July 25, 2000.
4Aug. 3, 2000 -Aug. 5, 2000
2000216.2004 - 2000218.2206
2.4.2.0FPA temperature contol re-established.  
5Aug. 8, 2000 - Aug. 12, 2000
2000221.1755 - 2000225.2046
Not applicableCooler outgas sequence  
6Aug. 18, 2000 - present
2000231.1640 - present
2.4.3.1FPA temperature is controlled.