Development and Test of a Fringe-Imaging Direct-Detection Doppler Wind Lidar for Aeronautics

DLR currently investigates the use of Doppler wind lidar as sensor within feedforward gust alleviation control loops on fast-flying fixed-wing aircraft. Such a scheme imposes strong requirements on the lidar system such as sub-m/s precision, high rate, high spatial resolution, close measurement ranges and sensitivity to mixed and pure molecular backscatter.We report on the development of a novel direct-detection Doppler wind lidar (DD-DWL) within these requirements. This DD-DWL is based on fringe-imaging of the Doppler-shifted backscatter of UV laser pulses in a field-widened Michelson interferometer using a fast linear photodetector.A prototype for airborne operation has been ground-tested in early 2018 against a commercial coherent DWL, demonstrating its ability of measuring close-range wind speeds with a precision of 0.5 m/s, independent of the actual wind speed.