1372 IEEE GEOSCIENCE AND REMOTE SENSING LETTERS, VOL. 15, NO. 9, SEPTEMBER 2018
Ship Detection in SAR Images Based
on Lognormal ρ-Metric
Meng Yang , Member, IEEE, and Chunsheng Guo, Member, IEEE
Abstract— Information geometry emerged from the study of
the geometrical structure of a manifold of probability distribu-
tions. It defines a Riemannian metric uniquely, which is Fisher
information metric. However, the classical Fisher metric method
has a limitation that it does not overcome the problem of
inhomogeneous and nonstationary clutter for ship detection in
synthetic aperture radar (SAR) images. By combing lognormal
model and the Riemannian geometry, this letter presents a mod-
ified Fisher metric (lognormal ρ-metric) based on information
geometry. Experiments show that lognormal metric for ρ in
the ship detection from SAR images can be tuned to increase
the performance of improving contrast between the object and
background, and reducing false alarms.
Index Terms— Information geometry, lognormal ρ-metric,
synthetic aperture radar (SAR) images, ship detection.
I. INTRODUCTION
S
YNTHETIC aperture radar (SAR) is an active remote
sensor, which makes it functional in all weather and day-
and-night operating conditions. SAR sensors have become an
important technology for the observation and surveillance of
the sea surface. In particular, the improved r esolution of SAR
images and the large amounts of open data being available
nowadays promote the development of new automatic ship
detection too ls in time. This is also evident from a large
number of research articles published on this subject. Marino
and Hajnsekand [1] tend to approach this topic from various
perspectives.
Among these, there are two fundamentally different means
of ship detection in SAR images: adaptive threshold and
feature representation. For the adaptive threshold algorithms,
constant false alarm rate (CFAR) detection of targets in heavy
sea clutter background is an important unit in the field of
automatic target recognitio n of SAR images [2]. However,
the difficulty of CFAR methods is to detect the ships appearing
on sea surfaces of varying degree of homogeneity and, at the
same time, to keep the false-alarm rate (FAR) down to a prede-
fined level. And, there are also many possible variations of the
shape and size of the target, guard, and background windows.
Manuscript received February 12, 2018; revised May 1, 2018; accepted
May 14, 2018. Date of publication May 30, 2018; date of current version
August 27, 2018. This work was supported by the Chinese National Natural
Science Foundation under Grant 61501152. (Corresponding author:
Meng Yang.)
The authors are with the College of Communication Engineering, Hangzhou
Dianzi University, Hangzhou 310018, China (e-mail: yangmeng@hdu.edu.cn).
Color versions of one or more of the figures in this letter are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LGRS.2018.2838043
Therefore, the final choice will be determined by the detection
problems at hand. Due to its simplicity and effectiveness, it is
expected that the distribution-based detection performance will
be improved by incorporating some novel analysis techniques.
Another approach to detect targets in a radar clutter
background is to extract the features of ship images [3].
Wang et al. [3] focus on the feature analysis of ships in high-
resolution SAR images and p ropose an optimizing algorithm
for ship detection. However, each feature representation for
ship detection has its own strengths and weaknesses, which
should be evaluated in relation to the practical application
scenarios. In addition, the resolution of most satellite SAR
images is often not high enough to extract detailed ship
inform ation. Therefore, some difficulty exists in employing
the ship features for d etection.
Information geometry has emerged from investigating the
relationship between differential geometry and information
theory. Theory of information geometry has experienced a very
fast development in the past few d ecades [4]. It has penetrated
into many other mathematical disciplines and has been making
great progress in theory and application in recent y ears [5].
Apart from classical Riemannian descendants, there are many
special metrics associated with various geometrical structures
in the theory of information geometry, sometimes in a rather
unexpected and subtle way. It provides the information sci-
ences with a more efficient method for constructing signal/data
abstract model. It has been usefully applied to various areas
and provides them with a new perspective to view the structure
of the investigated systems.
Our principal tool is the statistical manifold and metric-
topological constructions based on information geometry. The
aim of this letter is to show the benefits of statistical manifolds
suitable for feature analysis in SAR imagery and based on
information geometry theory. Statistical manifolds are the
representations of smooth families of probability density func-
tions. It allows differential geometry to be applied to problems
in ship target detection of SAR images.
The main contributions in the proposed method are as
follows: 1) ρ-metric construction for lognormal manifold with
high performance is exploited based on information geometry
and 2) a salience-based d escriptor method that exploits the
microstructure feature of statistical manifold.
II. P
ROPOSED METHODS
For this letter, we draw motivation from the modern math-
ematics thought and method, many of which are reflected in
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