radaraltimetrie

Radar altimetry is a remote sensing technique that uses a satellite-borne radar to measure the height of the Earth's surface above a reference ellipsoid. The altimeter emits microwave pulses toward the surface, records the round-trip travel time, and, with precise orbit data and atmospheric corrections, derives surface height. It is widely used for oceans and ice, and has applications over land in some contexts.

Principle: The instrument measures range, backscatter, and waveform. The round-trip time is corrected for ionospheric and tropospheric delays, tides, and instrument biases. Height is referenced to a geodetic ellipsoid using precise orbit determination. Most radar altimeters operate in the Ku-band; some missions use Ka-band. Dual-frequency systems help separate ionospheric effects, and waveform analysis yields information on sea state and surface roughness.

Platforms and products: Notable missions include TOPEX/Poseidon (1992–2005), Jason-1 (2001–2013), Jason-2 (2008–2019), Jason-3 (2016–present), CryoSat-2 (2010–present), Envisat/AltiKa (Ka-band, 2009–2012), and Sentinel-3 with the SRAL instrument (2016–present). Core data products are sea surface height with centimeter accuracy, significant wave height, ocean wind speed inferred from backscatter, and, over ice, ice-sheet elevations. Near-coastal and inland applications are more limited due to land interference and signal complexity.

Applications and limitations: Radar altimetry provides global sea-level monitoring, insights into ocean circulation and climate variability, and supports weather forecasting through SSH data. It contributes to ice-dynamics studies and water-resource monitoring in large rivers and lakes. Limitations include reduced accuracy near coastlines, land contamination, and biases from sea-state, instrument drift, and atmospheric corrections, which require calibration with tide gauges and models.