Gravimetric Methods – Spacecraft Altimeter Measurements

Satellite altimetry has become an important tool for studying the Earth. Here, we summarize the basic concepts of satellite radar altimeters, including how range is measured, how the precise orbit height is calculated, and how these are combined to determine sea surface height (SSH). Corrections needed to account for path delays of the radar pulse in the atmosphere and biases at the surface are described. These include the ionosphere, wet troposphere, and dry troposphere atmospheric corrections and the sea state bias and inverted barometer surface corrections. The calibration and verification of the SSH measurement is explained, using specific examples from the TOPEX/Poseidon and Jason-1 missions. We also comment on some geophysical applications of the altimeter measurement, including the ocean geoid, bathymetry, tides, and global mean sea level. Finally, we briefly discuss other types of satellite altimeters, including laser, delay-Doppler, and wide-swath altimeters.