Solid Earth geophysics and satellites

Abstract

Part of the frustrations in geophysics arise from the inability to adequately control the conditions for measurements and experiments. The earth is just too big to put into a conventional laboratory. Satellites provide a method of quickly‐making geophysical measurements globally.Early measurements of the earth and its gravity field were obtained from tracking satellite orbits. This led to experiments such as the geodetic satellites Geos‐1 and ‐2, which carried laser reflectors for improved tracking accuracy, and Geos‐3, which included a radar altimeter to measure directly ocean surface height. Radar altimeter technology has been improved and was tested on Skylab and used on the Seasat mission. These altimeter data make it possible to define the position of the geoid with respect to the spheroid more accurately over the oceans than over much of the continental masses. Uncertainties of the geoid's position over the oceans are 1 m to 5 m averaged over 5° by 5° areas. These uncertainties arise from our inability to account for all the variables, such as currents and tides, and from the lack of adequate data in some localities. The NASA Gravsat mission could provide a geoid accurate to 10 cm. This accuracy would make it possible to use future radar altimeter missions to measure ocean surface changes that deviate from the geoid. An additional product of radar altimetry would be a gravity map of the world that would include both oceans and continents. The map would be accurate to 1 to 5 mgal averaged over 1° by 1° areas.