Signal-to-noise ratio of pseudo-random noise continuous wave backscatter lidar with analog detection

Backscatter lidars are useful tools for range determination in various applications, particularly if they provide compact and robust set-ups with suitable light sources, efficient sensors and adequate signal processing. A promising perspective to achieve such requirements is offered by the Pseudo-Random Noise continuous wave (PRN cw) lidar technique, employing cw laser diodes as transmitter. Here the Signal-to-Noise ratio (SNR) of such lidar will be investigated in detail for the following cases: power (amplitude) modulation of the transmitted laser beam and analogue detection by an avalanche photodiode, surface detection. The SNR is calculated numerically, allowing selection of the factors limiting the lidar detection under various environmental conditions. A set of various measurements, obtained with a PRN cw lidar, employing a diode laser in the near IR spectral range and an avalanche photodiode will be presented. The results from the analytical and numerical study are compared with the experimental results. Various applications for the PRN cw lidar will be examined and critical factors influencing its detection performances discussed. Finally an outlook is provided for possible applications of such a lidar in specific atmospheric and surface measurements.