Solar contamination effects on the infrared channels of the advanced very high resolution radiometer (AVHRR)

Solar impingement on the advanced very high resolution radiometers (AVHRRs) near the terminator can contaminate the onboard radiometric calibration system and degrade AVHRR data. The solar contamination causes disagreement between the sensor-measured radiometric output of the onboard blackbody versus its bulk temperature measured by the platinum resistance thermometers. Despite the sun shield installed on the latest AVHRR unit, solar contamination can still contribute errors of more than 0.5 K in the 3.7 mum channel and 0.25 K in the long-wave infrared channels. The timescale and spectral characteristics of the contamination are analyzed to find the possible causes. In addition, stray light in Earth scenes is found whenever the radiometric calibration is contaminated. These effects occur as the spacecraft moves out of the shadow of the Earth at spacecraft sunrise. The intensity of the effects varies by orbit and season and is related to the solar zenith and azimuth angles at the spacecraft.