干旱区生态环境知识资源中心

Sensor intercalibration has been widely performed over low-latitude deserts and circumpolar regions where surface conditions are generally well characterized. This letter proposes a new method for intercalibrating visible bands of Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR) over homogenous land surfaces that differ in brightness, in order to improve calibration results. The method is based on the extended simultaneous nadir overpass events. Initially, the spectral band adjustment factors are calculated using surface reflectances in the MODIS 552 and 645-nm bands. Sensor differences related to atmospheric effects are corrected using MODIS atmospheric parameters and MODIS/AVHRR sun-target-sensor geometries. In view of excellent MODIS calibration accuracy, the residual MODIS-AVHRR difference may result from AVHRR calibration bias. A preliminary validation study over radiometric sites shows <1.0% uncertainty for the high-gain calibration and <2.0% uncertainty for the low-gain calibration. The proposed method allows sensor intercalibration over varying land surfaces, and contributes to a collection of sensor calibration and intercalibration results of AVHRR sensors.