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

Abstract

<jats:p>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.</jats:p> <jats:p>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.</jats:p> <jats:p>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.</jats:p>

Aeronautics Application of Direct-Detection Doppler Wind Lidar: An Adapted Design Based on a Fringe-Imaging Michelson Interferometer as Spectral Analyzer

“…In the detailed design process, a more comprehensive simulation should be used that also accounts for additional, real-world physical phenomena. Hence, the above-explained analytical model may be seen as the basis of a somewhat more comprehensive "end-to-end" lidar model of one specific implementation of a direct-detection Doppler wind lidar (DD-DWL) demonstrator (Section 2.3), realized and continuously augmented at DLR [43,46]. Due to the incorporation of the actual technical design, it necessarily loses its generality.…”

“…This is the reason why the analytical model of Equation ( 8) must be used in the overall aircraft GLA simulation procedure. Given its extent, we do not fully describe this model here (more thoroughly in [46]), but briefly touch upon it: referring to Figure 2, the basis of this model is again the lidar equation that delivers, for each laser pulse, the photon number (over time) collected by the optics as a function of the receiver variables, including the overlap function O(R). The next module derives the spatial distribution of the actual fringe produced by our Michelson interferometer as a convolution of the atmospheric scattering spectrum and the interferometer instrument function.…”

Influence of airborne LiDAR wavelength on the detection distance of clear air turbulence

“…In nonfatal aviation accidents, atmospheric turbulence is a leading cause of injuries to passengers and crew members 2 – 4 With global air traffic and rising concentrations of greenhouse gases (CO2) in the atmosphere, the frequency of CAT will continue to grow, seriously threatening aviation safety 4 – 6 Real-time detection and early warning of CAT have become hot spots in international aviation safety.…”

An Airborne Visible Light Lidar’s Methodology for Clear Air Turbulence Detection Based on Weak Optical Signal

“…Among atmospheric turbulence accidents, 40% are designated as caused by CAT [2]. It is a major cause of non-fatal aviation accidents, resulting in injuries to passengers and damage to aircraft structures; according to the Federal Aviation Administration (FAA), in the United States, an average of 58 passengers are injured each year, costing commercial airlines more than USD 100 million [3][4][5]. With the increases in global climate change and air traffic, the frequency of CAT occurrences will continue to rise, posing a significant threat to aviation safety [2,5].…”