Validation of the ERS-2 scatterometer ground processor upgrade

Due to gyroscopes malfunctions, the ERS-2 spacecraft cannot accurately be yaw steered. Moreover, the actual yaw angle of the spacecraft is unknown. Since the yaw angle is not known in advance and not periodic, the look-up tables-based original scatterometer processor is not able to compute accurate values for the backscattering coefficients from the measurements made. This implies the need for an upgraded wind scatterometer ground processor in order to obtain accurate backscattering coefficients. Moreover, the upgraded processor includes several other enhancements. This paper presents the results of the validation of the upgraded processor. The validation of the geometrical model is performed by comparing geometric parameters such as the incidence angle and the sub-satellite track heading. The radiometric performance of the upgraded processor is first evaluated with data acquired in nominal attitude, by comparing the backscattering coefficients. The radiometric performance of the upgraded processor is then further assessed with data acquired in degraded attitude. This is only possible over the calibration test site and over other selected land areas.