Theory of the double-edge molecular technique for Doppler lidar wind measurement

Abstract

The theory of the double-edge lidar technique for measuring the wind with molecular backscatter is described. Two high-spectral-resolution edge filters are located in the wings of the Rayleigh-Brillouin profile. This doubles the signal change per unit Doppler shift, the sensitivity, and improves measurement accuracy relative to the single-edge technique by nearly a factor of 2. The use of a crossover region where the sensitivity of a molecular- and an aerosol-based measurement is equal is described. Use of this region desensitizes the molecular measurement to the effects of aerosol scattering over a velocity range of +/-100 m/s. We give methods for correcting short-term, shot-to-shot, frequency jitter and drift with a laser reference frequency measurement and methods for long-term frequency correction with a servo control system. The effects of Rayleigh-Brillouin scattering on the measurement are shown to be significant and are included in the analysis. Simulations for a conical scanning satellite-based lidar at 355 nm show an accuracy of 2-3 m/s for altitudes of 2-15 km for a 1-km vertical resolution, a satellite altitude of 400 km, and a 200 km x 200 km spatial resolution.

Airborne wind lidar observations over the North Atlantic in 2016 for the pre-launch validation of the satellite mission Aeolus

“…Due to the Doppler effect, the frequency f 0 of the outgoing pulse is shifted upon The measurement principle of the Rayleigh channel relies on the double-edge technique (Chanin et al, 1989;Garnier and Chanin, 1992;Flesia and Korb, 1999;Gentry et al, 2000) and involves two bandpass filters (A and B) which are placed symmetrically around the frequency of the emitted laser pulse, as illustrated in Fig. 2(a).…”

Analysis on wind retrieval methods for Rayleigh Doppler lidar

“…[5][6][7][8][20][21][22][23][24][25] The molecular signal with Doppler shifts is spectrally broadened due to the random thermal motion of the molecules and Brillouin scattering. [26][27][28][29] As shown in Fig.…”

“…Coherent lidar measures the Doppler shift by beating the backscattered signal with light from a continuous-wave local oscillator laser, which often resolves the narrowband aerosol and cloud return and is commonly used for relatively small velocity detection. 3 The theory of direct-detection Doppler wind lidar was first described and realized by BenedettiMichelangeli et al 4 Various kinds of instruments, such as Fabry-Perot interferometer (FPI), [5][6][7][8][9][10] iodine absorption filter, 11,12 Fizeau interferometer, 13 and Mach-Zehnder interferometer, 14 have been chosen to discriminate the Doppler shift from the spectrally broadband Rayleigh-Brillouin return of molecules and spectrally narrowband Mie backscatter return of aerosol or cloud particles. The Doppler shift determination for direct detection has two typical implementations: edge technique and fringe-imaging technique.…”

“…The edge technique uses one or more narrowband filters to transform the Doppler shift into an irradiance variation, [5][6][7][8]15 whereas the fringeimaging technique retrieves the Doppler shift from the radial angular distribution or spatial movement of the interference patterns of an interferometer. 16,17 The double-edge technique as a powerful variation of the single-edge technique used for retrieving the instantaneous wind information has been demonstrated by Korb et al 7,8 It inherits the advantage of edge technique and extends its capabilities but has higher measurement precision. In the Atmospheric Dynamic Mission Aeolus (ADM-Aeolus) payload Atmospheric Laser Doppler Instrument (ALADIN), the double-edge technique will be used to analyze the molecular Rayleigh return with two FPIs as discriminator.…”

“…Different from the method of Chanin, Flesia and Korb described the wind determination algorithm for double-edge molecular technique in detail in 1999. 8 The measurement precision related to the instrument performance was discussed by McGill and Spinhirne through modeling the Doppler wind lidar techniques and making improvement on general instrument design. 17 In order to make the model more intuitive and conveniently implemented, McKay developed an another analytical model considering aperture finesse effects of FPI and background noise.…”