Abstract
Analysis of the radar echoes from a spaceborne altimeter gives information on sea surface height, wave height and wind speed, as well as other parameters over land and ice. The first spaceborne radar altimeter was pioneered on Skylab in 1974. Since then, there have been about 20 further missions, with several advances in the sophistication of hardware and complexity of processing with the aim of increased accuracy and precision. Because of that, the importance of regular and precise calibration and validation (“cal/val”) remains undiminished, especially with efforts to merge altimetric records from multiple missions spanning different domains and time periods. This special issue brings together 19 papers, with a focus on the recent missions (Jason-2, Jason-3, Sentinel-3A and HY-2B) as well as detailing the issues for anticipated future missions such as SWOT. This editorial provides a brief guide to the approaches and issues for cal/val of the various different derived parameters, including a synopsis of the papers in this special issue.
Highlights
Centre National d’Etudes Spatiales (CNES), 18 Avenue Edouard Belin, 31400 Toulouse, France; Abstract: Analysis of the radar echoes from a spaceborne altimeter gives information on sea surface height, wave height and wind speed, as well as other parameters over land and ice
Altimetric records of sea level can be compared with coastal tide gauges, measurements from offshore platforms, bottom-pressure recorders or surface buoys tied into the space geospatial framework via GNSS (Global Navigation Satellite System) technology
Altimeter data are critical for global observations of many essential climate variables, they can only be used quantitatively for long-term studies of climate change if they are accurately calibrated
Summary
Radar altimeters record the reflection of radio-wave pulses from the Earth’s surface, interpreting the timing, power and shape of the received echo waveform as range to the surface, indications of its roughness at various scales and, for snow, penetration depth [1]. The process of fitting a shape model to the observed return is known as “retracking”. The basic shape model for a homogeneous isotropic perfectly reflecting surface, such as the ocean, was developed by Brown [2] and Hayne [3]. The range information is combined with precise orbit predictions and detailed modelled or measured geophysical and environmental corrections to give the topography of the surface. This is further processed to obtain the sea surface height (SSH) with respect to the geoid (a reference geopotential surface). Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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