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The present paper describes the conceptual design and potential scientific and engineering applications of the Geodynamics Laser Ranging System (GLRS). The latter instrument is a spaceborne laser ranging and altimeter system. It is currently scheduled to be launched in the 1997 time frame as a facility on the first European polar orbiting platform which is being developed as part of the multiple satellite Earth Observing System (Eos). In the geodynamics or retroranging mode, the system will use the green and ultraviolet output from a subnanosecond pulse, frequency-tripled, Nd:YAG laser to measure the geometric range from the spacecraft to arrays of strategically placed groundbased retro-reflectors. The use of two colors, in conjunction with a two picosecond resolution streak tube receiver to measure the interpulse propagation delay introduced by atmospheric dispersion, will permit measurement of the geometric range with an absolute accuracy of 0.5 cms or better. Large radar cross- sections, on the order of a million square meters from the passive ground retroreflectors permit the use of small (0.18 m) receiver telescope diameters and optical trackers with the high slew rates and fast settling times necessary to interrogate large numbers of targets in a typical ten minute pass over the array. This data can be processed to provide decimeter accuracy satellite orbital ephemeris to collocated instruments, perform centimeter accuracy global geodetic measurements, provide data on the motion of tectonic plates or ice floes, and produce high spatial resolution information on regional crustal deformation caused by seismic, volcanic, or other forces such as oil or water withdrawal. Other potential scientific uses include the measurement of atmospheric surface pressure, ocean wave height and surface roughness, cloudtop heights, subnanosecond time transfer between widely separated sites, and longterm general relativity experiments. In the engineering arena, GLRS could provide preliminary surveys in support of land management applications or large scale engineering projects such as interstate highways as well as important information on long term ground stability relevant to the location of nuclear power plants, pipelines, aquaducts, dams, etc. The unconverted fundamental Nd:YAG radiation at 1.06 micrometers is directed to a nadir or near-nadir viewing altimetric channel and viewed by a somewhat larger (0.5 m diameter) telescope. A topographic channel provides both time-of-flight to the underlying terrain and nanosecond resolution waveforms to study geologic structures, transport properties associated with sand dunes and lava flows, and the thickness, growth, and decay of ice sheets. A second lower resolution digitizer provides data on cloud distributions and cloudtop heights.
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