Estimating significant wave height from SAR imagery based on
an SVM regression model
GAO Dong
1, 2
, LIU Yongxin
1
, MENG Junmin
2
, JIA Yongjun
3
, FAN Chenqing
2
*
1
College of Electronic and Information Engineering, Inner Mongolia University, Hohhot 010020, China
2
The First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China
3
National Satellite Ocean Application Service, State Oceanic Administration, Beijing 100081, China
Received 17 January 2017; accepted 31 May 2017
©The Chinese Society of Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
A new method for estimating significant wave height (SWH) from advanced synthetic aperture radar (ASAR) wave
mode data based on a support vector machine (SVM) regression model is presented. The model is established
based on a nonlinear relationship between σ
0
, the variance of the normalized SAR image, SAR image spectrum
spectral decomposition parameters and ocean wave SWH. The feature parameters of the SAR images are the input
parameters of the SVM regression model, and the SWH provided by the European Centre for Medium-range
Weather Forecasts (ECMWF) is the output parameter. On the basis of ASAR matching data set, a particle swarm
optimization (PSO) algorithm is used to optimize the input kernel parameters of the SVM regression model and to
establish the SVM model. The SWH estimation results yielded by this model are compared with the ECMWF
reanalysis data and the buoy data. The RMSE values of the SWH are 0.34 and 0.48 m, and the correlation
coefficient is 0.94 and 0.81, respectively. The results show that the SVM regression model is an effective method
for estimating the SWH from the SAR data. The advantage of this model is that SAR data may serve as an
independent data source for retrieving the SWH, which can avoid the complicated solution process associated
with wave spectra.
Key words: advanced synthetic aperture radar wave mode, support vector machine, significant wave height
Citation: Gao Dong, Liu Yongxin, Meng Junmin, Jia Yongjun, Fan Chenqing. 2018. Estimating significant wave height from SAR imagery
based on an SVM regression model. Acta Oceanologica Sinica, 37(3): 103–110, doi: 10.1007/s13131-018-1203-7
1 Introduction
Ocean wave is an important research topic in physical ocean-
ography, and a significant wave height (SWH) is one of the most
important parameters of an ocean wave observation. The classic-
al SWH inversion methods are an algorithm developed by the
Max Planck Institute (MPI), a partition rescale and shift al-
gorithm (PARSA), and a semiparametric retrieval algorithm
(SPRA). The SWH retrieved by the MPI is based on the nonlinear
mapping relation between the wave spectrum and the image
spectrum of a SAR image. Although good SWH results can be ob-
tained, MPI must run an ocean wave numerical model (such as
WAM) to obtain a first-guess spectrum (Hasselmann and Hassel-
mann, 1991; Hasselmann et al., 1996). The PARSA method is an
improvement and extension of the MPI method. Compared with
buoy measurements, the PARSA method yields better inversion
results, but it requires the multi-view cross-spectrum of a SAR
image as the input for inversion. The SPRA algorithm requires ex-
ternal synchronized wind field information, and the wind vector
parameter is used as an input to obtain ocean wave spectra (Mas-
tenbroek and de Valk, 2000). In analyzing the MPI and SPRA al-
gorithms for the wave spectrum inversion, Sun and Guan (2006)
outlined the advantages and disadvantages of the two. An im-
proved parameterized preliminary guessing spectrum model was
used as an input of the inversion, and the SAR image spectrum
was divided into wind and wave spectra to retrieve SWH.
At present, an empirical CWAVE model (Schulz-Stellenfleth
et al., 2007) and a CWAVE_ENV model (Li et al., 2011) are mainly
applied to retrieving the SWH. Both models are second-order
multiple regression models. The main difference between them
is the SAR data used to retrieve the SWH. To avoid the problem of
having too many unknown parameters in a polynomial regres-
sion model, the researchers put forward a new method based on
a support vector machine (SVM) regression model. The SVM is a
new machine learning algorithm generated within the frame-
work of a computational learning theory. The SVM is mainly used
for data classification, but a version of the SVM for regression was
proposed by Vapnik (1998), which has made it possible to apply
the SVM as a regression estimation model (Elbisy, 2015; Wang
and Bai, 2014; Xu et al., 2016). Compared with the classical ocean
wave spectrum inversion methods, the SVM regression model
does not need additional data as inputs; the SAR data can be
used as an independent data source for SWH extraction. Further-
more, compared with the second-order multiple regression mod-
els, it is able to solve the problem of poor learning, over learning
and poor generalization. The SVM-based SWH extraction meth-
od proposed in this paper provides a new choice for estimating
the SWH from the SAR imagery.
Foundation item: The National Key Research and Development Program of China under contract Nos 2016YFA0600102 and
2016YFC1401007; the National Natural Science Youth Foundation of China under contract No.61501130; the Natural Science
Foundation of China under contract No. 41406207.
*Corresponding author, E-mail: fanchenqing@fio.org.cn
Acta Oceanol. Sin., 2018, Vol. 37, No. 3, P. 103–110
DOI: 10.1007/s13131-018-1203-7
http://www.hyxb.org.cn
E-mail: hyxbe@263.net