Sea Clutter Distribution Modeling: A Kernel
Density Estimation Approach
Hongkuan Zhou, Yuzhou Li, and Tao Jiang
School of Electronic Information and Communications, Huazhong University of Science and Technology, Wuhan, China
{hongkuanzhou, yuzhouli, taojiang}@hust.edu.cn
Abstract—An accurate sea clutter distribution is crucial for
decision region determination when detecting sea-surface floating
targets. However, traditional parametric models possibly have
a considerable gap to the realistic distribution of sea clutters
due to the volatile sea states. In this paper, we develop a
kernel density estimation based framework to model the sea
clutter distributions without requiring any prior knowledge. In
this framework, we jointly consider two embedded fundamental
problems, the selection of a proper kernel density function
and the determination of its corresponding optimal bandwidth.
Regarding these two problems, we adopt the Gaussian, Gamma,
and Weibull distributions as the kernel functions, and derive the
closed-form optimal bandwidth equations for them. To deal with
the highly complicated equations for the three kernels, we further
design a fast iterative bandwidth selection algorithm to solve
them. Experimental results show that, compared with existing
methods, our proposed approach can significantly decrease the
error incurred by sea clutter modeling (about two orders of mag-
nitude reduction) and improve the target detection probability
(up to 36% in low false alarm rate cases).
I. INTRODUCTION
An important application for marine surveillance radar is to
detect sea-surface small floating targets such as buoys, human
divers, and small boats [1]. When detecting, the received target
signals at the radar are buried in the strong returned signals
reflected by the sea surface, referred to as sea clutters [2], [3].
It is known that better detection performance is achieved if
prior knowledge of sea clutters’ distribution can be acquired,
since by this a proper detection threshold can be determined
at the detector [4]–[6]. Therefore, an important question that
arises is how to accurately model the distribution of sea clutters
in the fluctuating sea state for small target detection.
By adopting various parametric models [7]–[10], there have
been extensive works attempting to characterize the distribu-
tion of sea clutters to obtain better detection performance.
In [7], the authors utilized the Gauss distribution to model
the amplitude of the sea clutter at a low-resolution radar.
With an increase in radar’s spatial resolution, the amplitude
distribution of the sea clutters was further extended from the
Gaussian to compound-Gaussian probability density functions
(PDFs) in [8] for small target detection. Gao et al. in [9]
This work was supported in part by the National Science Foundation of
China with Grant Numbers 61601192, 61631015, 61831013, and 61729101,
the Young Elite Scientists Sponsorship Program by CAST with Grant Number
2017QNRC001, the State Key Laboratory of Integrated Services Networks
(Xidian University) with Grant Number ISN19-09, and the Fundamental Re-
search Funds for the Central Universities with Grant Numbers 2016YXMS298
and 2015ZDTD012.
adopted the generalized Gamma distribution to describe the
statistical behaviors of sea clutters, and provided a parameter
estimation scheme by taking both of estimation precision and
applicable conditions into consideration. In [10], the authors
adopted the Weibull model in the constant false alarm rate
(CFAR) detector for radar detection and evaluated the involved
parameter optimization problem.
To summarize, the distributions of sea clutters adopted
in [7]–[10] for target detection are generally established as
parametric models. However, considering the two following
defects of the parametric models, a considerable gap possibly
exists between the fitted and realistic distribution of sea clut-
ters. Firstly, the parametric models can hardly depict the spiky
components in sea clutters, which is produced when the high-
resolution radar works at a low grazing angle or under dynamic
sea states [11]. Secondly, as the distribution of sea clutters
usually varies with different detection environments, assuming
a fixed parametric model for it cannot guarantee satisfactory
fitting performance in the varying detection environments and
thus degrades the detection performance.
Following these insights, the distribution of sea clutters
should be characterized by sufficiently analyzing the collected
data instead of assuming a parametric model. Inspired by
this, the kernel density estimation (KDE), a non-parametric
approach for estimating the PDF of a random variable, can be
adopted to reveal the distribution of the collected sea clutters.
Different from the methods in [7]–[10], the KDE method uti-
lizes smooth kernel functions to fit the realistic distribution of
the observed data without making any assumption on it, which
can effectively reflect the information of the spiky components
and flexibly adapt to the varying detection environments.
When applying the KDE method, it is of utmost importance
to determine two key parameters, namely the kernel function
and the bandwidth [12]. In [13], the Gaussian kernel and some
traditional bandwidth selectors such as the plug-in were adopt-
ed in the KDE method, which show good fitting performance
on random sequence samples. However, few works have
ever studied how the KDE method works in the sea-surface
target detection. In addition, whether there are other kernel
functions that can achieve better fitting performance than the
Gaussian kernel or not is still unclear. Furthermore, it is also
quite challenging to derive the optimal bandwidth for other
specialized kernels by the traditionally complicated bandwidth
selection methods such as the plug-in technique [13]. These
challenges impose restrictions on the application of KDE
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