Sensitivity Analysis of Brown Model Waveform in Radar Altimetry

 In satellite altimetry (radar altimetry), the altimeter emits a pulse, with known power, to the earth surface and receives it back continuously to determine of the sea surface height. The time series of the mean returned power is recorded individually at satellite as the so-called waveform. Analytical model for the waveform is first introduced by Brown, which consists of six parameters: significant wave height, epoch, skewness of surface, off-nadir angle, thermal noise and backscatter coefficient. The midpoint of the waveform has the main role in determining the distance between sensor and water surface (range). Then, assessing sensitivity of the model to these parameters plays an important role in determining reliability of the range parameter. In this study, the received waveform sensitivity analysis to the mentioned parameters is done for simulated waveform of JASON-2 radar altimetry mission. Then, in order to demonstrate effect of the parameters in observed JASON-2 data, 22 points are chosen over Persian Gulf and Oman Sea from cycle 208 and sensitivity analysis is performed using these points. Our results indicate that the mid-point of the waveform shape is less affected by significant wave height, skewness of surface and off-nadir angle but epoch of half height affects mid-point position significantly, which results in inaccurate range calculation. Because the process of determining the waveform components is a repetitive process, we discuss the choice of initial values of the parameters for using the least squares estimation.