Performance Analysis of a Multistatic Coherent Doppler Lidar

Wind velocity can be obtained using a light detection and ranging (lidar) system by measuring the Doppler shift of the scattered return from aerosols and particulates in the atmosphere. Doppler lidar systems for wind velocity measurements can be classified into two categories, coherent detection and direct (or incoherent) detection. Under each category there are novel approaches to measuring the return signal frequency. Regardless of the measurement mode, the goal for both types is to measure the frequency difference between the transmitted laser pulse and the scattered signal. This frequency shift is proportional to the velocity of the scatterers. How accurately these systems can measure the frequency shift, and thus the velocity, is dependent upon the system characteristics. Existing Doppler lidar systems employ monostatic configurations which require scanning a volume to obtain wind velocity and direction. Range resolution in these systems is normally obtained by using a pulsed laser system. This places a fundamental limit on the range-velocity resolution product. The purpose of this research is to investigate the feasibility of utilizing a multistatic configuration for measuring 3-dimensional vector winds. In the multistatic configuration, horizontal and vertical resolution are determined by the telescope field-of- view, laser divergence, and baseline separation distance between the laser and the telescope. This enables the use of a continuous-wave (CW) or long pulse laser transmitter (narrow spectral width) and eliminates the dependence between range and velocity resolution. The results of this research show that a multistatic pulsed Doppler lidar system will provide estimates of wind velocity with errors less than 1 m/sec and spatial resolution between 10 and 100 cm3 within the atmospheric boundary layer. Detailed signal-to-noise ratio calculations indicate that small transmit and local oscillator beams actually improve system performance.