The Impact of Receiver Aperture Design and Telescope Properties on LIDAR Signal-to-Noise Ratio Improvements

Range and sensitivities of lidar measurements in daylight are limited by sky background noise power (BGP). This is particularly important for Raman lidar techniques where the Raman backscattered signal is relatively weak. This often restricts Raman lidar measurements to nighttime where BGP is absent. The background noise elimination is particularly important in daytime measurements in case where full overlap between laser beam and receiver telescope field-of-view (FOV) is necessary. Results of numerical simulations for a vertically pointing Lidar show that significant improvements in Lidar signal to noise ratio (SNR) can be obtained, by minimizing the detected sky BGP. This can be, optimally achieved if the receiver telescope aperture is properly designed to track lidar target images, which are range dependant. In this context, the connection between receiver telescope field of view and optimum aperture size are examined. The SNR improvements, which can be obtained in this manner, translate to corresponding improvements in Lidar range for backscatter schemes including Raman and DIAL