Inter-Calibration of ERS AMI and MetOp ASCAT Backscatter Measurements
Reimer, Christoph; Hahn, Sebastian; Wagner, Wolfgang
Vienna University of Technology, Department of Geodesy and Geoinformation, Research Group Remote Sensing, AUSTRIA

ESA Living Planet Symposium 2013 Abstract

Inter-Calibration of ERS AMI and MetOp ASCAT backscatter measurements

Christoph Reimer, Wolfgang Wagner

Vienna University of Technology, Department of Geodesy and Geoinformation, Research Group Remote Sensing

Theme of Abstract: Calibration and Validation

Keywords: Calibration and Validation Results

Spaceborne scatterometer observations are used in a broad field of scientific applications ranging from weather and ocean-atmosphere interactions to applications over land and ice. Climate change research in these scientific fields requires long-term consistent data sets across various scatterometer missions. Similarities in the instrument technical design of ERS AMI and MetOp ASCAT facilitate the fusion of these data sets to a homogenous time series comprising more than 20 years of backscatter measurements for climate change research. In this paper an inter-calibration approach is presented, which will account for potential instrument related biases in ERS AMI and MetOp ASCAT backscatter measurements. The theoretical framework of this calibration method is based on the precise empirical modelling of the backscatter coefficient exhibited by extended area land-targets. The methodology is to initially monitor the end-to-end instrument performance of each scatterometer antenna separately, to infer potential degradation of instrument components affecting the radiometric accuracy. Deviations of the measured backscatter coefficients from an empirically estimated backscatter model gave an assessment of changes undergone by the instrument antennas. Compensating for of these effects is referred to as intra-sensor calibration, based on temporally stable and azimuthally isotropic characteristics of extended area land-targets. A temporally constant inter-calibration error can be assumed between AMI and ASCAT after intra-sensor adjustment. Accordingly the inter-calibration error can be estimated from the differences between the empirical backscatter models derived for intra-sensor calibration. Furthermore, additional extended area land-targets can be used to improve the assessment of the instrument bias between AMI and ASCAT, since the target requirements for inter-calibration differ slightly from those of intra-sensor calibration, in respect to the precondition of azimuthal isotropy. The calibration method presented is based on the determination of empirical backscatter models for AMI and ASCAT. Hence a robust estimation of these models is essential, to infer meaningful calibration results. The model estimation process will be discussed in detail in the final paper.