ABSTRACT
Laser radars (ladars) typically output both range and intensity images. The range images provide explicit three-dimensional (3D) information about objects. Intensity returns measure the reflectivity of objects. There are two kinds of ladar systems: direct-detection ladar and coherent ladar. A directdetection ladars ends out a simple pulse for each pixel, receives the returning signal energy, and estimates the range to that pixel by detecting the pulse in the return signal. A coherent ladar system sends out a signal on a carrier frequency, just as a standard AM or FM radio does. An advantage of directdetection over coherent systems is that direct detection gives improved range accuracy for a given set of lasers parameters, because direct-detection ladars are less susceptible to speckle and turbulence distortion of the signal. An advantage of coherent systems is that they can measure target motion using Doppler processing, whereas direct detection systems can measure motion only by sending repeated pulses and measuring the difference in range. Ladars are day/night sensors that operate well in a wide variety of weather conditions. They complement many traditional sensors (passive infrared, visible) and are useful in many applications. Figure 1 gives a simplified block diagram of ladar operation.
