Ka-band SAR interferometry studies for the SWOT mission

Daniel Esteban-Fernandez, Lee-Lueng Fu, Ernesto Rodriguez, Shannon Brown, Richard Hodges
<span title="">2010</span> <i title="IEEE"> <a target="_blank" rel="noopener" href="https://fatcat.wiki/container/6i67v2zuujhfvocqaapmnsoifm" style="color: black;">2010 IEEE International Geoscience and Remote Sensing Symposium</a> </i> &nbsp;
The primary objective of the National Research Council (NRC) Decadal Survey recommended SWOT (Surface Water and Ocean Topography) Mission is to measure the water elevation of the global oceans, as well as terrestrial water bodies (such as rivers, lakes, reservoirs, and wetlands), to answer key scientific questions on the kinetic energy of ocean circulation, the spatial and temporal variability of the world's surface freshwater storage and discharge, and to provide societal benefits on
more &raquo; ... climate change, coastal zone management, flood prediction, and water resources management. Radar altimetry has been a major achievement in the study of the Earth. Through the missions of TOPEX/Poseidon (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005), and its follow-on Jason (2001-present), and the Ocean Surface Topography Mission (OSTM)/Jason-2 (2008-), a 15+ year data record of the global ocean surface topography has been obtained, which will extend into the future. However, the spatial resolutions of these missions are not sufficient to address fundamental scientific questions such as: (1) the eddy currents of the ocean that contains 90% of the kinetic energy of ocean circulation, and (2) the variability of water storage and discharge over land, which is key to achieve understanding of the global water cycle. SWOT will use a new technique to measure water elevation that will provide an order-ofmagnitude improvement in resolution and accuracy that is required to address these scientific questions and to further our current knowledge of oceanography and land hydrology, while establishing a reference standard for future radar altimetry missions. The core technology for SWOT is the KaRIN instrument, originally developed from the efforts of the Wide Swath Ocean Altimeter (WSOA) [1], [2] . The KaRIn instrument (see Figure 1 ) will be complemented with the following suite of instruments:: a Ka-band interferometer, a dual-frequency nadir altimeter, and a multi-frequency water-vapor radiometer dedicated to measuring wet tropospheric path delay to correct the radar measurements. The interferometer's concept is as follows: radar pulses are transmitted from each antenna, and the radar echoes from each pulse are received by both. The interferometric phase difference between the coherent signals received by both antennas is essentially related to the geometric path length or range difference to the image point, which depends on the topography. Therefore, the knowledge of the range and the phase difference can be converted into an altitude for each image point. SWOT implements two Synthetic Aperture Radar (SAR) antennas (illustrated in the figure below), each one providing two separate beams at Ka-band (35.7 GHz). As a result, the total swath coverage provided by the interferometer is 120 km, at an unprecedented resolution of 1 km for the ocean (after on-board processing), and 50 m for land water.
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