1,639 research outputs found
Ship detection with spectral analysis of synthetic aperture radar: a comparison of new and well-known algorithms
The surveillance of maritime areas with remote sensing is vital for security reasons, as well as for the protection of the environment. Satellite-borne synthetic aperture radar (SAR) offers large-scale surveillance, which is not reliant on solar illumination and is rather independent of weather conditions. The main feature of vessels in SAR images is a higher backscattering compared to the sea background. This peculiarity has led to the development of several ship detectors focused on identifying anomalies in the intensity of SAR images. More recently, different approaches relying on the information kept in the spectrum of a single-look complex (SLC) SAR image were proposed. This paper is focused on two main issues. Firstly, two recently developed sub-look detectors are applied for the first time to ship detection. Secondly, new and well-known ship detection algorithms are compared in order to understand which has the best performance under certain circumstances and if the sub-look analysis improves ship detection. The comparison is done on real SAR data exploiting diversity in frequency and polarization. Specifically, the employed data consist of six RADARSAT-2 fine quad-polacquisitions over the North Sea, five TerraSAR-X HH/VV dual-polarimetric data-takes, also over the North Sea, and one ALOS-PALSAR quad-polarimetric dataset over Tokyo Bay. Simultaneously to the SAR images, validation data were collected, which include the automatic identification system (AIS) position of ships and wind speeds. The results of the analysis show that the performance of the different sub-look algorithms considered here is strongly dependent on polarization, frequency and resolution. Interestingly, these sub-look detectors are able to outperform the classical SAR intensity detector when the sea state is particularly high, leading to a strong clutter contribution. It was also observed that there are situations where the performance improvement thanks to the sub-look analysis is not so noticeable
Multi-headed deep learning-based estimator for correlated-SIRV Pareto type II distributed clutter
This paper deals with the problem of estimating the parameters of heavy-tailed sea clutter in high-resolution radar, when the clutter is modeled by the correlated Pareto type II distribution. Existing estimators based on the maximum likelihood (ML) approach, integer-order moments (IOM) approach, fractional-order moments (FOM), and log-moments (log-MoM) have shown to be sensitive to changes in data correlation. In this work, we resort to a deep learning (DL) approach based on a multi-headed architecture to overcome this problem. Offline training of the artificial neural networks (ANN) is carried out by using several combinations of the clutter parameters, with different correlation degrees. To assess the performance of the proposed estimator, we resort to Monte Carlo simulation, and we observed that it has superior performance over existing approaches in terms of estimation mean square error (MSE) and robustness to changes of the clutter correlation coefficient
AN ARTIFICIAL INTELLIGENCE APPROACH TO THE PROCESSING OF RADAR RETURN SIGNALS FOR TARGET DETECTION
Most of the operating vessel traffic management systems experience problems, such
as track loss and track swap, which may cause confusion to the traffic regulators and
lead to potential hazards in the harbour operation. The reason is mainly due to the
limited adaptive capabilities of the algorithms used in the detection process. The
decision on whether a target is present is usually based on the magnitude of the
returning echoes. Such a method has a low efficiency in discriminating between the
target and clutter, especially when the signal to noise ratio is low. The performance
of radar target detection depends on the features, which can be used to discriminate
between clutter and targets. To have a significant improvement in the detection of
weak targets, more obvious discriminating features must be identified and extracted.
This research investigates conventional Constant False Alarm Rate (CFAR)
algorithms and introduces the approach of applying ar1ificial intelligence methods to
the target detection problems. Previous research has been unde11aken to improve the
detection capability of the radar system in the heavy clutter environment and many
new CFAR algorithms, which are based on amplitude information only, have been
developed. This research studies these algorithms and proposes that it is feasible to
design and develop an advanced target detection system that is capable of
discriminating targets from clutters by learning the .different features extracted from
radar returns.
The approach adopted for this further work into target detection was the use of
neural networks. Results presented show that such a network is able to learn
particular features of specific radar return signals, e.g. rain clutter, sea clutter, target,
and to decide if a target is present in a finite window of data. The work includes a
study of the characteristics of radar signals and identification of the features that can
be used in the process of effective detection. The use of a general purpose marine
radar has allowed the collection of live signals from the Plymouth harbour for
analysis, training and validation. The approach of using data from the real
environment has enabled the developed detection system to be exposed to real clutter
conditions that cannot be obtained when using simulated data.
The performance of the neural network detection system is evaluated with further
recorded data and the results obtained are compared with the conventional CFAR
algorithms. It is shown that the neural system can learn the features of specific radar
signals and provide a superior performance in detecting targets from clutters. Areas
for further research and development arc presented; these include the use of a
sophisticated recording system, high speed processors and the potential for target
classification
Investigation of Ground Target Detection Methods in Fully Polarimetric Wide Angle Synthetic Aperture Radar Images
Target detection is a high priority of the Air Force for the purpose of reconnaissance and bombardment. This research investigates and develops methods to distinguish ground targets from clutter (i.e. foliage, landscape etc.) in Wide Angle Synthetic Aperture Radar (WASAR) images. WASAR uses multiple aspect angle SAR images of the same target scene. The WASAR data was generated from a pre-release software package (XPATCH-ES) provided by the sponsor (WL-AARA). A statistical analysis and feature extraction is performed on the XPATCH-ES data. Polarimetric and wide angle covariance matrices are estimated and analyzed. From an analysis of the wide angle covariance matrix it is shown that natural clutter has in general a uniform radar return for changing aspect angles, whereas the radar return for a target varies. Based on this analysis, two new wide angle algorithms, the WASAR Whitening Filter and the Adaptive WASAR Whitening Filter (AWWF) are developed. The target detection performance of polarimetric and multi aspect angle image combining algorithms are quantified using Receiver Operating Characteristic curves and target to clutter ratios. It is shown that wide angle processing provides superior target detection performance over polarimetric processing. Combinations of wide angle and polarimetric algorithms were used to achieve a 13.7 dB processing gain in target to clutter ratio when compared to unprocessed images of the target scene. This represents a significant improvement in target detection capabilities
Constant False Alarm Rate Target Detection in Synthetic Aperture Radar Imagery
Target detection plays a significant role in many synthetic aperture radar (SAR) applications, ranging from surveillance of military tanks and enemy territories to crop monitoring in agricultural uses. Detection of targets faces two major problems namely, first, how to remotely acquire high resolution images of targets, second, how to efficiently extract information regarding features of clutter-embedded targets. The first problem is addressed by the use of high penetration radar like synthetic aperture radar. The second problem is tackled by efficient algorithms for accurate and fast detection. So far, there are many methods of target detection for SAR imagery available such as CFAR, generalized likelihood ratio test (GLRT) method, multiscale autoregressive method, wavelet transform based method etc. The CFAR method has been extensively used because of its attractive features like simple computation and fast detection of targets. The CFAR algorithm incorporates precise statistical description of background clutter which determines how accurately target detection is achieved. The primary goal of this project is to investigate the statistical distribution of SAR background clutter from homogeneous and heterogeneous ground areas and analyze suitability of statistical distributions mathematically modelled for SAR clutter. The threshold has to be accurately computed based on statistical distribution so as to efficiently distinguish target from SAR clutter. Several distributions such as lognormal, Weibull, K, KK, G0, generalized Gamma (GGD) distributions are considered for clutter amplitude modeling in SAR images. The CFAR detection algorithm based on appropriate background clutter distribution is applied to moving and stationary target acquisition and recognition (MSTAR) images. The experimental results show that, CFAR detector based on GGD outmatches CFAR detectors based on lognormal, Weibull, K, KK, G0 distributions in terms of accuracy and computation time.
Bispectrum- and Bicoherence-Based Discriminative Features Used for Classification of Radar Targets and Atmospheric Formations
This chapter is dedicated to bispectrum-based signal processing in the surveillance radar applications. Detection, recognition, and classification of the targets by surveillance radars have various applications including security, military intelligence, battlefield purposes, boundary protection, as well as weather forecast. One of the particular and effective discriminative features commonly exploited in modern radar automatic target recognition (ATR) systems is the micro-Doppler (m-D) contributions extracted from joint time-frequency (TF) distribution. However, a common drawback of the energy-based strategy lies in the impossibility to retrieve additional particular information related to frequency-coupling and phase-coupling contributions containing in the radar backscattering. Phase coupling contains additional discriminative features related to individual target properties. Bispectrum-based strategy allows retrieving a phase-coupled data containing unique discriminative features related to individual target properties. Bispectrum tends to zero for a stationary zero-mean additive white Gaussian noise (AWGN), providing smoothing of AWGN in TF distributions. Hence, bispectrum-based approach allows improving extraction of robust discriminative features for ATR radar systems
Neural Network-Based Multi-Target Detection within Correlated Heavy-Tailed Clutter
This work addresses the problem of range-Doppler multiple target detection in
a radar system in the presence of slow-time correlated and heavy-tailed
distributed clutter. Conventional target detection algorithms assume
Gaussian-distributed clutter, but their performance is significantly degraded
in the presence of correlated heavy-tailed distributed clutter. Derivation of
optimal detection algorithms with heavy-tailed distributed clutter is
analytically intractable. Furthermore, the clutter distribution is frequently
unknown. This work proposes a deep learning-based approach for multiple target
detection in the range-Doppler domain. The proposed approach is based on a
unified NN model to process the time-domain radar signal for a variety of
signal-to-clutter-plus-noise ratios (SCNRs) and clutter distributions,
simplifying the detector architecture and the neural network training
procedure. The performance of the proposed approach is evaluated in various
experiments using recorded radar echoes, and via simulations, it is shown that
the proposed method outperforms the conventional cell-averaging constant
false-alarm rate (CA-CFAR), the ordered-statistic CFAR (OS-CFAR), and the
adaptive normalized matched-filter (ANMF) detectors in terms of probability of
detection in the majority of tested SCNRs and clutter scenarios.Comment: Accepted to IEEE Transactions on Aerospace and Electronic System
Improved Shape Parameter Estimation in Pareto Distributed Clutter with Neural Networks
The main problem faced by naval radars is the elimination of the clutter input which is a distortion signal appearing mixed with target reflections. Recently, the Pareto distribution has been related to sea clutter measurements suggesting that it may provide a better fit than other traditional distributions. The authors propose a new method for estimating the Pareto shape parameter based on artificial neural networks. The solution achieves a precise estimation of the parameter, having a low computational cost, and outperforming the classic method which uses Maximum Likelihood Estimates (MLE). The presented scheme contributes to the development of the NATE detector for Pareto clutter, which uses the knowledge of clutter statistics for improving the stability of the detection, among other applications
A False-alarm-controllable Modified AdaBoost Wake Detection Method Using SAR Images
A false-alarm-controllable modified AdaBoost-based method is proposed for detecting ship wake from sea clutter in synthetic aperture radar (SAR) images. It reformulates the wake detection problem as a binary classification task in the multifeature space. The update strategy of the sample weights in the original AdaBoost is modified for wake detection. First, a detection result confidence factor is designed to deal with class imbalance between sea clutter and ship wake; then, the AdaBoost is further modified as a false alarm rate (FAR) controllable detector by introducing penalty parameters to adjust weights update strategies for the sea clutter. Meanwhile, the multifeature space is spanned by a novel frequency peak height ratio (FPHA) feature and four salient features. FPHA is proposed to enhance the separation between the wake and sea clutter, which is computed from the amplitude spectrum peak of the image after the Fourier transform. Experimental results show that the proposed detector can tackle the imbalanced data problem and flexibly control FAR by adjusting penalty parameters. Moreover, improved detection probability is also achieved compared with existing methods
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