21 December 1998 Absolute calibration of the EnviSat-1 radar altimeter
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The EnviSat-1 satellite will embark an innovative radar altimeter. The calibration of the measurements of range from this instrument will be performed using novel techniques. The range measurement will be calibrated absolutely by establishing the actual geocentric sea-level along the sub- satellite tracks. These tracks are located in a limited and well-controlled region in the western Mediterranean and will include a number of fully-equipped individual sites which will provide higher confidence in the overall analysis, combined with data from the whole area at lower weight. The determination of the geocentric sea-level is performed using tide gauges and geodetic means such as leveling and floating GPS receivers. The altimeter sea-level is derived from the altimeter range corrected for propagation effects and sea- state bias, and a precise restitution of the trajectory of the satellite. These measurements comprise three vectors: range, orbital height and sea-surface height. The difference between orbital-height minus range, and sea-surface height provides the bias. The backscatter coefficient measured by previous altimeters has not been absolutely calibrated. An emerging application of the RA-2 in investigation of surface properties has identified the need to perform this calibration. A number of techniques are under study to determine the feasibility of meeting this need, including the use of well-controlled natural targets, the use of the altimeter receiver as a passive radiometer in order to determine its gain and the use of a transponder to return a precisely known return echo power to the radar.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Monica Roca, Richard Francis, "Absolute calibration of the EnviSat-1 radar altimeter", Proc. SPIE 3498, Sensors, Systems, and Next-Generation Satellites II, (21 December 1998); doi: 10.1117/12.333667; https://doi.org/10.1117/12.333667

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