Caliration Technology For HY-2Radar Altimeter Sea Surface Height

The satellite radar altimetry has become a powerful tool in oceanography andclimate change studies, by providing amount of valuable globally distributed oceandynamic observations with the unprecedented precision, which serves a vital functionin a range of fields including marine disaster prevention and reduction, ocean resourcedevelopment and global change etc.Higher requirements are put forward to thequantitative application of the observation in light of furthering and studying of theradar altimeter derived data, and extension of the study field. Nevertheless, thestringently accurate calibration is essential prerequisite for wide application. TheHY-2, launched in August,2011, the in orbit validation of which suggests that thevarious technical indicators cater for basic needs in practicality. However, for the mostimportant ocean dynamic environment parameter (sea surface height), the accurate,reliable and standard process for absolute calibration and production evaluation hasnot achieved yet, significantly limiting quantitative application of altimetryproduction.Therefore, the paper performs research around calibration of altimetry seasurface height and evaluation of production of HY-2, to make a breakthrough inaltimetry errors correction, crossover calibration and absolute in situ calibration, andthus to carry out the crucial technologies. The results would be incorporated intocalibration/validation sub-system of HY-2satellite radar altimeter after further testand assessment, offering technical supports for operational altimeter data process andcalibration/validation of HY-2satellite ground data processing system.Calibration for radar altimeter involves complex data processes and crossesmultiple knowledge domains. The paper demonstrates the function that the altimeterserved and performs study in the global change context, and then presents thealtimetry principle and key technology. The calibration related components for HY-2radar altimeter are detailed in the paper including errors correction, for instance, seastate, atmospheric delay and geophysical effects, and crossover calibration, in situcalibration and the proposal of dedicated calibration site construction. The specifiedresearches and innovations are listed as following: 1) The corrections including range corrections and geophysical effects give rise tosignificant influence to altimetry, which are analyzed in detail in the paper. Thecomparison between Jason-2GDR corrections and independentmodel/algorithm corrections shows a agreement between former and latter witha root-mean-square-error of2.969cm, indicating the independent solution isprecision and feasible in calibration and validation for altimeters.2) Based on independent models/algorithms, the crossover calibration results areconcluded with a mean relative bias of0.26cm and rmse of6.61cm, indicatingthat the precision of crossover calibration reach the equivalent level from globalhomogeneous altimeter.3) Absolute in situ calibration of altimeter give the calibration parameters in anabsolute sense, to this end, a feasible method with a precision of1.88±0.20cmis presented to acquire nadir from onshore tidal gauge to perform absolutecalibration. The method caters for operational in situ altimeter calibration.4) The construction of dedicated calibration site is analyzed from several aspects,thus providing theoretical basis and tichnogical support for domestic dedicatedcalibration site construction.