Laser Heterodyne Radars and Lidars

Abstract

The title of this chapter is so contradictory that it needs special clarification before commencing the detailed discussion of the chapter matter. The term RADAR emerged in 1941 as an acronym for radio detection and ranging. Thus, the two words “laser radar” being put together represent first contradiction. It sounds even more curios, considering the fact that both words are acronyms: LASER stands for light amplification by stimulated emission of radiation. The combination “laser radar” was introduced in the early 1960s in order to represent new remote-sensing devices based on lasers. The very first laser remote-sensing systems were basically a compilation of traditional radar concepts designed for the same purpose: to detect and measure coordinates of moving remote targets. Much smaller wavelength and shorter pulses ignited enthusiasm of obtaining much more precise measurements with more compact systems. Those first laser systems were designed by people proficient in radar technology, which explains partially why the term “laser radars” was readily accepted. Soon, however, new generation of people came to the scene, educated in the field of optics, and eager to establish their own language in rapidly expanding area of laser systems. Their concern was mainly the peculiar optical phenomena related to optical scattering in atmosphere. Since laser systems developed for this particular purpose had nothing to do with detection and ranging of moving targets, the quest for new term for that kind of laser remote-sensing systems was initiated. As a result, the term LIDAR – light detection and ranging – emerged. It is also possible to encounter the third acronym: LADAR for laser detection and ranging. After some short period of friendly battles between the groups of supporters of these different names for basically very similar technical concepts, the areas of responsibilities were divided as follows: systems designed for tracking of moving targets, space-ships docking, or military applications are now commonly recognized as laser radars, whereas the systems for remote sensing of atmosphere and monitoring wind vectors are referred to as lidars.