Abstract
The first laser range finder (1961) used direct detection and since then a great number of direct detection system have become operational. Work on coherent laser radars began after the discovery of the CO2 laser by Patel in 1964. Since then coherent laser radars have been developed for range finding, wind measurements, vibration sensing, obstacle avoidance and advanced imaging. There are however very few operational coherent laser radars probably due to complexity and high costs. The main advantages of coherent detection over direct detection systems are instantaneous Doppler and shot noise limited detection. Many of laser radar functions can also be realized with direct detection. The direct detection systems are in general simpler. Recent development of efficient short wavelength laser sources might change this in favor of coherent systems but it might also lead to efficient direct detection systems. In this talk we will investigate performance for hard target laser radars using either type of detection. System examples for range finding, target imaging and obstacle avoidance/terrain following will be analyzed. Important parameter variations beside the system parameters include target/background characteristics, atmospheric attenuation and turbulence.