Performance Analysis of the Improved Second-Order Retracking Algorithm and Its Application for Significant Wave Height Estimation

Jiasheng Tian^1,2*Jin Wang¹Jian Shi¹

• ¹Huazhong University of Science and Technology, Wuhan, China
• ²Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources of the People's Republic of China, Beijing, China

Compared to the measurement bias of sea surface height (<5 cm), the measurement bias of significant wave height (SWH) is around 10% (typically resulting in a 40 cm deviation for a 4 m SWH), making it challenging to meet the increasing demand for disaster prevention and reduction. In this study, the presented second-order retracking algorithm (MLE6) is investigated to specify furtherly the accuracy of SWH inversion. MLE6 includes skewness coefficient (s) and electromagnetic bias coefficient (em), in addition to four conventional parameters. The effects of non-linear or non-Gaussian random ocean surfaces on estimating SWH are analyzed and an improved adaptive algorithm is presented by considering the real radar point target response (PTR). The echoes simulated by MLE6 were compared with those of a three-term convolution model (Brown model) that considered the non-Gaussian rough sea surface elevation distribution. MLE6 showed closer alignment with the Brown model compared to the conventional model (MLE4), and exhibited better accuracy in SWH inversion. The improvement achieved by MLE6 in inverting SWH was approximately 3–7 cm. MLE6 was refined into an improved adaptive algorithm to address the realistic radar PTR. Finally, testing done with the surface wave investigation and monitoring (SWIM) measurements demonstrated that MLE6 could increase the accuracy of SWH inversion by an additional 4 cm compared to MLE4. The improved adaptive algorithm, which incorporated the actual PTR of SWIM, further improved the accuracy of SWH inversion by 3–4 cm when compared to the adaptive algorithm used by SWIM.