Calibration of PRISM and AVNIR-2 Onboard ALOS “Daichi”

The Advanced Land Observing Satellite (ALOS); nicknamed ldquoDaichirdquo was successfully launched on January 24, 2006, and it continues to work very well. This paper describes the calibrations of two optical instruments onboard ALOS, which are the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) and Advanced Visible and Near-Infrared Radiometer type 2 (AVNIR-2). PRISM consists of three panchromatic radiometers and is used to derive a digital surface model (DSM) with high spatial resolution, which is an objective of the ALOS mission. AVNIR-2 has four radiometric bands from blue to near infrared, which are used for investigating regional environment issues such as land-use and land-cover classifications, and disaster monitoring. In this paper, we introduce the calibration and validation plan, methodologies, accuracy assessments of the standard products, image quality evaluations for PRISM and AVNIR-2, and their results. Geometric calibration is important in generating a precise DSM by a stereo pair image of PRISM. The relative geometric calibrations of both PRISM and AVNIR-2 are conducted by evaluating accuracies within one scene and evaluating sensor alignments as absolute calibration. For absolute geometric accuracies, we achieved 8.1 m for nadir-looking images and 9.3 m for forward- and backward-looking images of PRISM; we also achieved 114.2 m for AVNIR-2. PRISM is also radiometrically calibrated both relatively and absolutely. PRISM relative radiometric calibration is accomplished by using acquired images over homogeneous targets, such as oceans, deserts, ice, and snow areas, as well as nighttime observation. Simultaneously observed images with calibrated AVNIR-2 are used for absolute radiometric calibration by cross-calibration. The absolute radiometric accuracy of the PRISM nadir-looking radiometer is similar to that of AVNIR-2.