https://cdn.earthdata.nasa.gov/conduit/upload/5182/KeywordsCommunityGuide_Baseline_v1_SIGNED_FINAL.pdf 23.9 2026-05-13T10:52:13.516Z https://gcmd.earthdata.nasa.gov/KeywordViewer/scheme/instruments/faef1e3c-e201-4fbc-8f7e-5ab2818c0a62 ALTIMETERS Date=2021-08-04 User Id=sritz Entity=AltLabel Operation=INSERT System Note=insert AltLabel New Value=id: null category: primary text: ALTIMETERS language code: en The altimeter is a 13.5 GHz near-nadir pointing radar which measuresthe range to the surface of the ocean. The height measurement fromthe altimeter to the ocean surface is useful in various oceanographicapplications. Determination of sea surface topography is useful formarine gravity determinations, seafloor bathymetry estimations, anddynamic circulation of the oceans.In addition, wave height and wind speed can be measured by altimeters.The characteristics of the radar return signal are determined by theocean surface. The wave height is found from the sharply risingleading edge slope of the return wave form, and the amplitude of theocean return signal is a measure of the backscatter coefficient whichis related to wind speed.The earliest returns from the transmitted radar pulse come from thewave crests with contributions increasing with time from reflectorsdeeper in the waves. The plateau region of the wave form, which is ata fairly constant level is reached at about the time that the firstreflectors from the wave troughs are received. As a result the returnsignal has a steep slope in low sea states and a relatively gentleslope in high wave heights. The mathematical model relating the shapeof the leading edge to significant wave height assumes that the seasurface is Gaussian and linear. Amplitude of the ocean return signalis normalised by an automatic gain control (AGC) loop. This AGCsetting is a measure of the backscatter coefficient (radarcross-section, s0) at the surface which depends on wind speed. 2021-08-04 17:01:28.0