Estimation of Temporally Evolving Typhoon Winds and Waves from Synthetic Aperture Radar

Abstract

Abstract : The long-term goal of this project is to develop a methodology for using synthetic aperture radar (SAR) data to improve characterization of the winds and waves generated by typhoons in the western Pacific Ocean. The specific objective of the project is to develop a variational assimilation algorithm based on the SWAN model to estimate the near-surface typhoon wind field from SAR data. Third-generation wave spectrum models such as SWAN can be used to predict wind-generated waves. Combining SWAN and a model relating the SAR-image spectrum to the computed wave spectrum, one can predict the SAR-image spectrum which results from a known wind field. Using variational data assimilation, this relationship can be inverted to estimate the wind field from SAR data. The focus of this effort is to extend an existing SAR assimilation algorithm to enable the estimation of surface wind fields from SAR data. An assimilation algorithm has been developed to estimate the ocean-wave field for a near-shore region for stationary conditions using SAR data. The algorithm is variational in nature and is based on the SWAN 40.51 ocean-wave-spectrum model coupled to the nonlinear SAR-spectrum model of Hasselmann and Hasselmann. For this case, the algorithm is used to estimate the boundary conditions for SWAN that result in a wave-spectrum prediction which best fits the SAR data.