A semiempirical algorithm for SAR wave height retrieval and its validation using Envisat ASAR wave mode data
- PDF / 922,471 Bytes
- 8 Pages / 595 x 842 pts (A4) Page_size
- 110 Downloads / 188 Views
A semiempirical algorithm for SAR wave height retrieval and its validation using Envisat ASAR wave mode data WANG He1,2∗ , ZHU Jianhua1 , YANG Jingsong2 , SHI Chaoying3 1 2
3
National Ocean Technology Center, State Oceanic Administration, Tianjin 300112, China State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China National Center of Ocean Standard and Metrology, State Oceanic Administration, Tianjin 300112, China
Received 5 March 2011; accepted 12 October 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2012
Abstract Many synthetic aperture radar (SAR) wave height retrieval algorithms have been developed. However, the wave height retrievals from most existing methods either depend on other input as the first guess or are restricted to the long wave regime. A semiempirical algorithm is presented, which has the objective to estimate the wave height from SAR imagery without any prior knowledge. The proposed novel algorithm was developed based on the theoretical SAR ocean wave imaging mechanism and the empirical relation between two types of wave period. The dependency of the proposed model on radar incident and wave direction was analyzed. For Envisat advanced synthetic aperture radar (ASAR) wave mode data, the model can be reduced to the simple form with two input parameters, i.e., the cutoff wavelength and peak wavelength of ocean wave, which can be retrieved from SAR imagery without any prior knowledge of wind or wave. Using Envisat ASAR wave mode data and the collocated buoy measurements from NDBC, the semiempirical algorithm is validated and compared with the Envisat ASAR level 2 products. The root-mean-square-error (RMSE) and scatter index (SI) in respect to the in situ measurements are 0.52 m and 19% respectively. Validation results indicate that, for Envisat ASAR wave mode data, the proposed method works well. Key words: significant wave height, SAR, retrieval, validation
cording to the different spectra inversion algorithm, these schemes fall into two categories, each of which has its own drawback. Schemes of the first category, such as Max-Planck Institute (MPI) (Hasselmann and Hasselmann, 1991; Hasselmann et al., 1996), semiparametric retrieval algorithm(SPRA) (Mastenbroek and de Valk, 2000), partition rescaling and shift algorithm (PARSA) (Schulz-Stellenfleth et al., 2005), and others (e.g. Sun and Kawamura, 2009), have to rely on a first guess wave spectrum or additional wind information to invert the spectrum. The Hs retrievals of them, therefore, are not independent. In a separate set of schemes, including European Space Agency(ESA)’s algorithm (Johnsen et al., 2002; Collard et al., 2005) and Lyzenga’s (2002) unconstrained algorithm, the inverted spectra are restricted to the long wave regime.
1 Introduction The energy of ocean waves is conventionally represented by the significant wave height (Hs ). Hs is one of the most important parameters of ocean wave for offshore engineering. T
Data Loading...
