Aeolus' Response Calibration

Abstract

Aeolus was the first Doppler wind lidar in space. During its almost 5 years lifetime after launch in August 2018 it made use of two lasers operating at a wavelength of 354.8 nm. In contrast to coherent wind lidars that use heterodyning, the direct-detection approach applies high-resolution interferometry and hence requires accurate and regular calibration, but also allows measurements outside aerosol-loaded areas. The Instrument Response Calibration (IRC) plays an essential role in the Aeolus processing chain for L1B wind data, and helps to ensure the precision and accuracy of L2B wind data disseminated to the scientific community. The IRC is used to determine spectral characteristics of the receiver and the relationship between the instrument measurement output data (the response) and the actual frequency shift. We explain fundamental aspects of IRC, such as the monitoring of IRC-related parameters, the quality assessment of the receiver channels' calibration curves and the utilization of IRC-based parameters in the wind retrieval algorithm.