ABSTRACT
This chapter reviews some of the science of these systems and considers the kind of coherent optical sources are that are required. Radio and microwaves have long been used for the detection of remote objects through the use of radar techniques. The shorter wavelengths allow better angular resolution, the very short pulses that can be generated with light can allow better distance resolution, the wavelengths involved can allow significant backscatter from aerosols, and the photon energies involved can allow the unique property of detecting specific atomic or molecular species. The simplest form of lidar, and the form that is closest in principle to radar, is basic laser ranging. In this case a pulsed laser is used to send out a short pulse of light to a hard target. A measurement of the time taken till the return signal comes back gives the distance to the object. Additional information can be obtained if the frequency of the reflected light is analysed.
