Overview of Instrument Response Calibrations

Kurzfassung

The Instrument Response Calibration (IRC) constitutes a fundamental part of the Aeolus processing chain and the basis for accurate and precise wind information provided to the global user community. The IRC is a crucial instrument mode for the wind measurement and has, hence, been extensively investigated with the ALADIN Airborne Demonstrator already before launch of the Aeolus satellite. IRCs are used to determine the relationship between the Doppler frequency shift on the backscattered light, i.e. the wind speed, and the frequency response of the Rayleigh and Mie spectrometers. This is achieved by sampling a frequency range of 1 GHz in steps of 25 MHz around the nominal laser frequency for the wind measurement. Whereas Aeolus wind measurements (WVM) are obtained under an off-nadir viewing angle of 35°, IRCs are performed in nadir viewing mode, thereby trying to avoid the atmospheric horizontal wind component along the line-of-sight as well as the component of the satellite velocity. The special importance of the IRC mode has changed with time caused by the experiences gained after the launch of Aeolus.