Altimeter Sea Surface Height Absolute Calibration Method

Radar altimeter is one of the most important microwave remote sensing instruments carried by marine dynamic environment satellite and it has played important role in many domains, such as oceanography, geodesy, and geophysics. HY-2 (Haiyang-2 satellite), the first marine dynamic environment satellite of China, will be launched in 2011 and it will carry a radar altimeter. In-situ calibration is one of the essential steps for the quantitative remote sensing. Calibration on sea-surface height includes absolute calibration with in-situ data and cross-calibration between different satellites. In this dissertation, the absolute calibration methods on sea- surface height of satellite altimeter are studied and some suggestion on HY-2 altimeter calibration is given.Three methods about absolute calibration of sea surface height are introduced and their relative merits and applicability are compared. The in-situ data from tide station, offshore platform and GPS buoy is used in these methods respectively. This dissertation is focused on the calibration method with tide station data.Errors of sea surface height by altimeter and tide station are analyzed and the corresponding correction models are given. Altimeter data correction includes atmospheric path delay, sea state bias, tide effects and inverse barometer effect. Tide data correction includes tide effects and inverse barometer effect. Correction of atmospheric path delay includes dry troposphere correction, wet troposphere correction and ionosphere correction. Tide effect includes ocean tide, solid earth tide and pole tide. The EGM2008 gravity field model is introduced in detail and it is used to correct the altimeter data and tide station data into the same datum plane.Sea surface height measurement of Jason-2 altimeter's pass063 was calibrated with Sheshan tide station data from Oct. 3 2009 to Dec. 23 2010. Altimeter data and tide data were executed quality control and data matching and 41 pairs of data were selected. Correlation coefficient of sea-surface height between tide station data and Jason-2's data is 0.94. The absolute deviation of Jason-2's calibration is -28.34±9.9cm, which is larger than Jason-2's official measurement precision of 3.4cm. This difference may be related to many factors, such as the location of tide station, tide model and less data points.Based on this study, the tide station data can be used in HY-2 sea-surface height calibration. Long time series data from more than one offshore tide stations and local tidal model should be used to improve precision of results.