Daytime performance simulation of PN-code modulated micro-Joule lidar

Laser radar (LIDAR) has proven to be beneficial for retrieving atmospheric information. While most lidars to date have been mono-pulse systems that record the responses to individually transmitted pulses of light at significant energy levels (a few tenths to a few Joules), more research is now focusing on low-power, eye-safe systems. One method for obtaining range information from lidars transmitting with low peak power lasers is to implement pulse code modulation wherein the lidar transmits a CW pseudo-noise code modulated signal. This paper presents a simulation of the pn-code modulated lidar scheme. By choosing an appropriate maximal-length code and bit length, atmospheric ranges of interest can be sensed by statistical correlation analysis of the temporal return signal. A key issue concerning the viability of this approach is the signal to noise ratio (SNR). The averaging time needed to achieve an acceptable SNR in daylight conditions, when noise is high, is compared to that of a conventional monopulse lidar system. Input parameters and considerations such as detector limitations and model noise levels are discussed