Both the surface water hydrology and ocean surface topography communities recognize the importance of wide-swath altimetry for its capability of acquiring high-resolution elevation measurements (status of the science and technology in support of the advanced wide-swath altimeter). The technology for SWOT is a Ka-band Radar INterferometer (KaRIN, 0.86 cm wavelength) that has been developed from the efforts of the Wide Swath Ocean Altimeter (WSOA; Fu, 2003; Fu and Rodriguez, 2004). KaRIN is essentially a smaller version of SRTM with two Ka-band SAR antennae at opposite ends of a 10 m boom and both antennae transmitting and receiving the emitted radar pulses along both sides of the orbital track. Look angles are limited to 4.5° providing a 120 km wide swath. Interferometric SAR processing of the returned pulses yields a 5 m azimuth and 10 m to 70 m range resolution, with elevation precision of ± 50 cm. Polynomial based averaging over areas less than 1 km² increases the height precision to less than ± 1 cm. At Ka band, the interferometer will penetrate clouds and relies on subtle canopy openings to penetrate to any underlying water surfaces (openings of only 20% are sufficient).