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Satellite laser ranging (SLR) has been used for over two decades in the study of a variety of geophysical phenomena, including global tectonic plate motion, regional crustal deformation near plate boundaries, Earth''s gravity field, the orientation of its polar axis and rate of spin, lunar dynamics and general relativistic studies. The subcentimeter precision of the technique is now attracting the attention of a new community of scientists, notably those interested in high- resolution ocean, ice, and land topography. Over the next several years, the international SLR network will provide an essential link between the geocentric terrestrial reference frame (as presently defined by the international VLBI and SLR networks) and two new oceanographic satellites, ERS-1 and TOPEX-Poseidon, which will range to sea and ice surfaces using microwave altimeters. The combined SLR/altimetry data set will provide precise orbits, improved gravity models, and estimates of the marine geoid. The latter are necessary to infer the dynamic sea surface topography and will enable measurements of parameters important to an understanding of global change, such as mean sea level and ice sheet thickness. Laser tracking of oceanographic satellites from multiple sites as they overfly special calibration towers equipped with tide gauges will also provide periodic estimates of microwave altimeter bias. The few-centimeter precision orbits determined by the SLR network will be used as ''ground truth'' data in the intercomparison and performance evaluation of developmental space radio-navigation systems such as GPS (TOPEX/Poseidon) and PRARE (ERS-1). Future spaceborne two-color SLR instruments, such as NASA''s geoscience laser ranging system (GLRS), can monitor the tectonically-induced motions of tide gauges by bouncing laser pulses off of collocated retroreflectors. Similar systems can measure the barometric loading over the open ocean. When used as transmitters in spaceborne or airborne altimeters, the narrow beamwidths and short pulsewidths available from lasers can provide high spatial resolution (both horizontal and vertical) topographic data over land and ice in support of a diverse set of science applications.
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