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Definition:
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An instrument for altimetry that transmits and receives pulses of microwave radiation. Satellite radar altimeters (including ERS-1 and 2, Envisat and others) typically operate in the Ku band (13.5 ghz; 22 mm wavelength) and were designed primarily for oceanographic monitoring. Because of their relatively large footprint (several km), they are best suited for measuring elevationsof gently-sloping regions of the ice sheets. Steep or undulating terrain produces complex waveforms and difficulties in achieving accurate estimates of range (i. E. Distance). Surface and volume scattering also affect the radar pulse and create uncertainty in the effective depth of the reflecting horizon. Surface dielectric properties and roughness that cause scattering are time-varying and introduce errors in calculations of elevation change. Recent radar altimeters use synthetic aperture processing (see insar) that increases resolution and decreases slope errors relative to earlier radar altimeters. The Shuttle Radar Topography Mission (SRTM) used a C-band radar (5.6 ghz; 54 mm wavelength) and synthetic aperture processing to obtain an accurate map of surface elevations with near-global coverage. Cryosat-2, launched in April 2010, will also use insar to map glaciers and ice sheets.
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