Methodology · Radar altimetry

Radar altimetry - sea surface height and inland water levels

Measures sea surface height, significant wave height, and inland water levels from nadir-pointing radar pulse returns; good for sea level rise monitoring, ocean circulation, and river/lake hydrology.

How it works

Nadir pulse-limited or SAR-mode altimeter measures round-trip travel time to the surface. Corrections applied for ionosphere, wet/dry troposphere, and tides. TOPEX/Poseidon -> Jason-1/2/3 -> Sentinel-6 constitutes an unbroken record since 1992. Wikipedia: Radar altimeter

Topics this serves

Topic

Fit

Inland waterfirst choice

Ocean currentsfirst choice

Sea-surface-height gradients are the standard satellite route to broad geostrophic surface circulation.

Sea level and ocean dynamicsfirst choice

Sea statefirst choice

significant-wave-height retrieval

Floodingsuitable

Glacier and ice-sheet masssuitable

radar-altimetry

Ocean heat contentsuitable

Altimetry contributes sea-level/steric-height constraints used in OHC and Earth-energy-imbalance estimates.

Space geodesysuitable

Terrain elevationsuitable

Radar altimetry (CryoSat-2 SIRAL) maps ice-sheet surface elevation and elevation change over Greenland and Antarctica at coarse grid spacing.

Coastal erosionadequate

Droughtadequate

Groundwater and terrestrial water storageadequate

surface-water-component

Ocean surface windsadequate

along-track altimeter wind-speed context

Existing implementations

Demonstrated

HY-2D Radar Altimeter via HY-2D
HY-2D carries an operational radar altimeter for ocean dynamic environment measurements.
Poseidon-4 SAR Altimeter via Sentinel-6B
Poseidon-4 is Sentinel-6B primary SAR radar altimeter for sea-surface height and inland-water measurements.
Ka-band Radar Interferometer (KaRIn) via Surface Water and Ocean Topography (SWOT)
KaRIn is the primary SWOT radar-interferometry payload for water-surface elevation.
Poseidon-3C Altimeter via Surface Water and Ocean Topography (SWOT)
Poseidon-3C/Jason-class nadir altimeter collects SWOT nadir-gap sea-surface-height measurements.
SAR Interferometer Radar Altimeter (SIRAL) via CryoSat-2
SIRAL is the Ku-band SAR/interferometric radar-altimeter payload on CryoSat-2.
HY-2B Radar Altimeter via HY-2B
HY-2B ALT is a dual-frequency radar altimeter for sea-surface-height ocean dynamics observations.
Surface Waves Investigation and Monitoring instrument (SWIM) via CFOSAT
SWIM is a Ku-band multi-beam altimeter; existing radar-altimetry method fits nadir/off-nadir ranging, while a wave-spectra method gap is proposed separately.
Synthetic Aperture Radar Altimeter (SRAL) via Sentinel-3B
SRAL demonstrates radar altimetry for sea-surface topography and inland-water height on Sentinel-3B.
HY-2C Radar Altimeter via HY-2C
HY-2C ALT is the radar-altimetry payload.

Capable, undemonstrated

2C Degrees Water-Risk Signals

Sources

[1]Wikipedia: Radar altimetercommunity2026-05-22

Methodology

Edited from public sources by SpectraWorks editorial. See the data dictionary for field definitions.

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Radar altimetry - sea surface height and inland water levels. EO-Atlas, SpectraWorks B.V. https://eo-atlas.org/topics/methodologies/radar-altimetry (CC BY 4.0)

BibTeX

@misc{eoatlas:topics:methodologies:radar-altimetry,
  title = {Radar altimetry - sea surface height and inland water levels},
  author = {{EO-Atlas}},
  publisher = {SpectraWorks B.V.},
  note = {CC BY 4.0},
  url = {https://eo-atlas.org/topics/methodologies/radar-altimetry}
}