Study On The Backscattering Coefficient In-orbit Calibration Of HY-2 Altimeter Using A Reconstructive Transponder

Transponder, as an in-orbit calibration instrument of radar altimeter, has been proposed in the 1980 s.At the early 2000 s, in-orbit altimeter calibration mission based on a bent pipe transponder was carried out and the measured value of backscattering coefficient reached appropriate precision. In the 1990 s, a reconstructive transponder based on reconstructing returning signals was available. However, none in-orbit backscattering coefficient calibration mission of radar altimeter has utilized the reconstructive transponder yet. HY-2 is the first marine dynamic environment satellite of China and the radar altimeter as its main payload has turned into operational application. In order to increase the measuring precision of sea wind measured by the HY-2 altimeter, an in-orbit calibration work for it was needed.HY-2 in-orbit calibration campaign using the reconstructive transponder has begun in 2012.This thesis proposes an in-orbit calibration approach of HY-2 altimeter using the reconstructive transponder and The scaling factor has been calculated after conducting in-orbit calibration experiments. Then the scaling factor is used in correcting backscattering coefficient measured by the altimeter. Finally, we compared the value from HY-2 with the result from Jason2 and the consistent result verifies the feasibility and accuracy of the approach. The main contents are as follows(The rest of the abstract use ?transponder? to call the reconstructive transponder that is applied in HY-2 in-orbit calibration work):1. The development of domestic and international altimeter and operational theory of altimeter is introduced. The structure, key technology and dominating mode of HY-2 altimeter are elaborated well.2. The development process of external calibration method for an radar altimeter system is presented, from passive corner reflector to active transponder. Focus on the structure, principle, work mode and performance indicators of the transponder.3. An in-orbit backscattering coefficient calibration approach for HY-2 altimeter is proposed, which uses the transponder. The radar cross section of the transponder could be gotten through a self-calibration system, where one metal circle act as a standard reflector in the near. The value of scaling factor can be calculated by processing data from the experiment of in-orbit calibration of the altimeter.4. Calculate the backscattering coefficient from HY-2 after calibration and combine the backscattering coefficients from HY-2 before calibration and corresponding result from Jason2, proving the feasibility and accuracy of the approach put forward in the thesis.