Abstract

Doppler lidar systems are typically classified into two types: (incoherent) direct detection and (coherent) heterodyne detection [1]. In direct detection, spectral analysis is directly performed on the backscattered radiation from the laser illuminated target, as opposed to the beat signal resulting from the coherent mixing of backscattered light with a reference beam. Unlike heterodyne detection which requires optimization of the spatial overlap between the (complex) backscatter and reference fields, direct detection is more robust to phase aberration and/or depolarization incurred by the probing laser beam (e.g. through the atmosphere or a liquid medium). Furthermore, direct detection lidars can inherently determine whether the Doppler shift is either a red or a blue shift while heterodyne detection lidars only measures the magnitude of the shift unless additional expensive components (e.g. acousto-optic modulator frequency shifter) are introduced in the optical setup.

© 2015 IEEE