Conference Paper

On the use of polarimetric SAR data for ship detection

Authors:
  • Canada Centre for Remote SEnsig
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Abstract

The polarization information is investigated for ship detection, using the polarimetric Convair-580 SAR. Ocean and ship polarimetric signatures are analysed within the incidence angle range 45°-70° using a data set off the Nova Scotia coast. It is shown that among the classical linear polarizations HH, VV, and HV, the polarization HH gives the best ship-sea contrast at grazing angles, even though the sea clutter is the lowest for the HV polarization. Circular polarizations perform better than the HH polarization at lower incidence angles. The polarization entropy is investigated for use in ship detection. It permits a significant improvement of the ship-sea contrast for incidence angles up to 60°. For larger incidence angles, the increasing heterogeneity of the ocean scattering mechanisms reduces the efficiency of the polarization entropy tool for ship discrimination

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... From the analysis provided by Liu et al. [22] and shared by other authors [28], it was shown that the quad-polarimetric mode provides the best detection performance, followed by the dual co-polarization combination and . A second type of polarimetric ship detectors is based on physical scattering properties of targets and ships [2], [23]- [25], [28] (some of them exploited the difference in coherence or degree of polarization shown by ships and sea clutter. The technique presented in this paper, namely Geometrical Perturbation -Polarimetric Notch Filter (GP-PNF) was developed in [1]- [3] and evaluates the differences in the polarimetric signature between the sea and targets. ...
... The entropy is defined as: (4) are the probabilities of each eigenvalue and can be calculated as: (5) where are the eigenvalues. As mentioned in the previous section, the entropy (or more generally other measures of depolarization) was proposed for ship detection [23]. The rationale behind this choice is that the sea has a rather deterministic polarimetric behavior that leads the pixels inside the averaging window to be rather coherent to each other. ...
... This may appear contradicting the fact that the best single channel for ship detection was demonstrated to be [23], [6]. An interpretation of these results is that the co-polarizations allow to characterize more precisely the sea polarimetric behavior and, therefore, to identify more accurately its complementary (target) subspace. ...
Article
The surveillance of maritime areas is a major topic for security aimed at fighting issues as illegal trafficking, illegal fishing, piracy, etc. In this context, Synthetic Aperture Radar (SAR) has proven to be particularly beneficial due to its all-weather and night time acquisition capabilities. Moreover, the recent generation of satellites can provide high quality images with high resolution and polarimetric capabilities. This paper is devoted to the validation of a recently developed ship detector, the Geometrical Perturbations Polarimetric Notch Filter (GP-PNF) exploiting L-band polarimetric data. The algorithm is able to isolate the return coming from the sea background and trigger a detection if a target with different polarimetric behavior is present. Moreover, the algorithm is adaptive and is able to account for changes of sea clutter both in polarimetry and intensity. In this work, the GP-PNF is tested and validated for the first time ever with L-band data, exploiting one ALOS-PALSAR quad-pol dataset acquired on the 9th of October 2008 in Tokyo Bay. One of the motivations of the analysis is also the attempt of testing the suitability of GP-PNF to be used with the new generations of L-band satellites (e.g., ALOS-2). The acquisitions are accompanied by a ground truth performed with a video survey. A comparison with two other detectors is presented, one exploiting a single polarimetric channel and the other considering quad-polarimetric data. Moreover, a test exploiting dual-polarimetric modes (HH/VV and HH/HV) is performed. The GP-PNF shows the capability to detect targets presenting pixel intensity smaller than the surrounding sea clutter in some polarimetric channels. Finally, the quad-polarimetric GP-PNF outperformed in some situations the other two detectors.
... The experiments on SIR-C quad-pol images displayed the effectiveness of Cameron decomposition on ship detection. Touzi [8] explored the polarization information in ship detection and found out that background and was stable under incident angles from 18 • to 45 • [29]. Yin deduced three parameters for ship and oil detection based on the X-Bragg model and proved their ability in discriminating targets from lookalikes [30]. ...
... Remote Sens. 2016, 8,751 3 of 16 farm target and the ocean background and was stable under incident angles from 18° to 45° [29]. Yin deduced three parameters for ship and oil detection based on the X-Bragg model and proved their ability in discriminating targets from lookalikes [30]. ...
... Remote Sens. 2016,8, 751 ...
Article
A few previous studies have illustrated the potentials of compact polarimetric Synthetic Aperture Radar (CP SAR) in ship detection. In this paper, we design a ship detection algorithm of CP SAR from the perspective of computer vision. A ship detection algorithm using the pulsed cosine transform (PCT) visual attention model is proposed to suppress background clutter and highlight conspicuous ship targets. It is the first time that a visual attention model is introduced to CP SAR application. The proposed algorithm is a quick and complete framework for practical use. Polarimetric features-the relative phase δ and volume scattering component-are extracted from m-δ decomposition to eliminate false alarms and modify the PCT model. The constant false alarm rate (CFAR) algorithm based on lognormal distribution is adopted to detect ship targets, after a clutter distribution fitting procedure of the modified saliency map. The proposed method is then tested on three simulated circular-transmit-linear-receive (CTLR) mode images, which covering East Sea of China. Compared with the detection results of SPAN and the saliency map with only single-channel amplitude, the proposed method achieves the highest detection rates and the lowest misidentification rate and highest figure of merit, proving the effectiveness of polarimetric information of compact polarimetric SAR ship detection and the enhancement from the visual attention model.
... The existing polarimetric SAR systems have quad-polarized imaging modes which have proved very effective in ship detection [9], [10]. Studies for determining the best polarization combinations composed from the four polarimetric channels (HH, HV, VH and VV) for ship detection were performed by Yeremy [11], Touzi [12], [10], and Liu [13], [14]. These studies showed that quad-pol and dual-pol data often yield higher accuracy than single channel data. ...
... > η for a ship ≤ η for ocean (12) where ...
Article
Quad-pol data are generally acknowledged as providing the highest performance in ship detection applications using SAR data. Yet quad-pol data have half the swath width of single and dual-pol data and are thus less useful for maritime surveillance, where wide area coverage is crucial. Compact polarimetry (CP) has been proposed as a compromise between swath width and polarization information. The circular-transmit-linear-receive (CTLR) CP data have certain engineering advantages over other CP configurations. CP data may be used to reconstruct a reduced quad-pol covariance matrix (termed pseudo-quad, or PQ, data) and the potential of these data in terrestrial applications has recently been demonstrated. We present some of the first results on the use of CTLR data and reconstructed quad-pol data for ship detection. We use Radarsat-2 fine-quad (FQ) data to examine 76 ships over a range of incidence angles and ship orientations at low to moderate wind speeds. We examined the ship detection performance of full quad-pol and full-PQ data; several dual-pol configurations suggested in the literature, HV and PQ HV and the raw CTLR data. We find that the ship detection performance of the PQ HV data is the strongest of all the detectors we examined, with performance that was comparable to quad-pol data. Other strong performers were HV and CTLR data.
... In the co-polarization mode, HH polarization is known to have a higher contrast between sea and ship than VV polarization. Therefore, it was expected that this would yield a better ship detection performance [24]. TerraSAR-X used a total of four images, and these images were captured in Songdo, Korea, and the Kerch Strait between the Black Sea and the Azov Sea. ...
... For polarization, both SAR images used the HH mode. In the same polarization mode, because it is widely known that HH polarization shows a higher contrast between sea and ship than that shown by VV polarization, it was expected that this would yield a better ship detection performance [24]. TerraSAR-X used a total of four images, and these images were captured in Songdo, Korea, and the Kerch Strait between the Black Sea and the Azov Sea. ...
Article
Full-text available
Synthetic aperture radar (SAR) images have been used in many studies for ship detection because they can be captured without being affected by time and weather. In recent years, the development of deep learning techniques has facilitated studies on ship detection in SAR images using deep learning techniques. However, because the noise from SAR images can negatively affect the learning of the deep learning model, it is necessary to reduce the noise through preprocessing. In this study, deep learning vessel detection was performed using preprocessed SAR images, and the effects of the preprocessing of the images on deep learning vessel detection were compared and analyzed. Through the preprocessing of SAR images, (1) intensity images, (2) decibel images, and (3) intensity difference and texture images were generated. The M2Det object detection model was used for the deep learning process and preprocessed SAR images. After the object detection model was trained, ship detection was performed using test images. The test results are presented in terms of precision, recall, and average precision (AP), which were 93.18%, 91.11%, and 89.78% for the intensity images, respectively, 94.16%, 94.16%, and 92.34% for the decibel images, respectively, and 97.40%, 94.94%, and 95.55% for the intensity difference and texture images, respectively. From the results, it can be found that the preprocessing of the SAR images can facilitate the deep learning process and improve the ship detection performance. The results of this study are expected to contribute to the development of deep learning-based ship detection techniques in SAR images in the future.
... The cross-polarization (HV) channel is able to provide better ROC curves compared with the co-polarization ones (HH and VV). This outcome has been also observed by other researchers [3,21,40,41]. According to the Bragg model, sea clutter has a very low (or even null) backscattering in the cross-channel, leading in many circumstances to an increased contrast. ...
... In the performed test, it seems that the cross-polarization (HV) provides the best ROC curves for all of the experiments. This has been also reported by several researchers [3,40]. Additionally, this result is in line with the assumption that the sea can be modeled as a Bragg surface [9,51], which assumes a null cross-polarization. ...
Article
Full-text available
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.
... dual-pol SAR performs better than single-pol (Liu & Meek, 2005;Touzi, 1999). This is intuitively expected since the amount of information extracted from SAR data gradually decreases by moving from quad-pol through single-pol data and from amplitude and phase to amplitude only data. ...
... Full PQ, coherent PQ HH-VV, and PQHV Merged CP detector: RH-RV-PQHV This is a total of nine systems. We do not examine any of the observed single-pol systems as it has been reported in the literature that single-pol systems have much weaker detection performance with respect to dual-pol and quad-pol systems (Liu & Meek, 2005;Touzi, 1999). Note that the HH-VV configuration will not be available in the RCM Ship Detection imaging mode, only in the Medium Resolution and Low Resolution modes. ...
Article
Full-text available
The RADARSAT Constellation Mission (RCM) planned to be launched in 2018 is designed to support maritime surveillance requirements in which ice, wind, oil pollution, and ships are to be monitored by providing wide swath beam modes. In this article, we introduce the first analysis of ship detection performance using simulated RCM data. We report ship detection performance using a likelihood ratio test (LRT) for three wide swath RCM imaging modes: Ship Detection (25 m), Low Resolution (100 m), and Medium Resolution (50 m). These beam modes were assessed for a number of dual-polarimetric (dual-pol) systems, including the standard linear polarizations as well as compact polarimetry (CP). These data were simulated from RADARSAT-2 Fine Quad (FQ) mode in the three RCM modes. Furthermore, the detection performance of the pseudo-quad data reconstructed from the simulated circular transmit, linear receive data is also investigated and compared to the other systems’ performance for the three RCM modes. The receiver operating characteristic curves are used in this study as the basic measure of detection performance for all beam modes and all detectors. We found that the compact polarimetric SAR detectors outperform the conventional linear dual-pol detectors at the three RCM modes for ship detection for medium to high incidence angles. At steep angles, the performance of the two polarization configurations was comparable. Our study confirmed that detection performance improved as incidence angle and spatial resolution increased. We also investigated the impact of the ship orientation with respect to the radar beam and found that detection performance was generally higher when ship was oriented perpendicular to the radar beam.
... The backscatter response in various polarization bases provides complete information about the target and thus can be advantageous for their characterization. The PS technique has been widely used to discriminate point targets and distributed targets (Touzi 1999;Evans et al. 1988;Strzelczyk and Porzycka-Strzelczyk 2014;Choe et al. 2019) in diverse applications viz., land cover feature extraction, crop classification, etc. (Huang et al. 2017;Jafari, Maghsoudi, and Zoej 2015;Dos Santos et al. 2009;Verma and Haldar 2019;Mandal, Bhattacharya, and Rao 2021). (Touzi 1999) investigated the polarimetric signature of ships and oceans. ...
... The PS technique has been widely used to discriminate point targets and distributed targets (Touzi 1999;Evans et al. 1988;Strzelczyk and Porzycka-Strzelczyk 2014;Choe et al. 2019) in diverse applications viz., land cover feature extraction, crop classification, etc. (Huang et al. 2017;Jafari, Maghsoudi, and Zoej 2015;Dos Santos et al. 2009;Verma and Haldar 2019;Mandal, Bhattacharya, and Rao 2021). (Touzi 1999) investigated the polarimetric signature of ships and oceans. The circular polarization is suggested to perform better than the linear polarization at a lower incidence angle for ship detection. ...
Article
The synthesized received power for every wave ellipticity (−45°≤χ≤45°), and orientation (−90°≤ψ≤90°) angle describe the polarization signature (PS) of a target. Thus, it provides valuable information for target characterization. The PS of various crops at two frequencies (C- and L-band) is assessed in this study for various crops. It is observed that the volume scattering mechanism is mainly produced at C-band by the tall and medium height crops viz. Sugarcane, Maize, and Finger Millet. The depolarized power is evident from such targets with the pedestal height (PH) (0≤PH≤1) values, ranging between 0.34 and 0.22. In contrast, we noticed that the surface scattering mechanism is dominant for short-height crops such as Chilli, Turmeric, and Paddy. It is also interesting to note the differential backscatter response for a few common polarization states widely varies for the two frequencies between −5.72 dB to −1.5 dB for Paddy, Sugarcane, and Maize.
... In this way, the WT is able to characterize the local regularity of the signal: the existence of discontinuities in the original images produces large wavelet coefficients, while homogeneous areas, on the contrary, present small coefficients [18]. In [20] and [22], instead, polarimetric analyses are employed to detect ship targets over the sea clutter pointing out that, generally, SAR polarimetry improves ship-detection performance. ...
... Furthermore, in many real cases, when ϕ = 0, the double reflection component may be lower than the noise floor level and undetectable on SAR images. However, it has been demonstrated that on real SAR images, the RCS relevant to the cross-polarized channels is not negligible and can be useful to improve the performance of the SAR detectors [10], [20]. For these reasons, and for the sake of completeness, the authors have added here also the results relative to the cross-polarized channel. ...
Article
Full-text available
Synthetic aperture radar (SAR) sensors represent one of the most effective means to support activities in the sector of maritime surveillance. In the field of ship detection, many SAR-based algorithms have been proposed recently, but none of them has ever considered the electromagnetic aspects behind the interactions of SAR signals with the ship and surrounding waters, with the detection step and rate strongly influenced by relative thresholding techniques applied to the SAR amplitude or intensity image. This paper introduces a novel model to evaluate the radar cross section (RCS) backscattered from a canonical ship adapted, to the case at issue, from similar existing models developed for, and applied to, urban areas. The RCS is modeled using the Kirchhoff approximation (KA) within the geometrical optics (GO) solution and, following some assumptions on the scene parameters, derived by empirical observations; its probability density function is derived for all polarizations. An analysis of the sensitiveness of the RCS to the uncertainty on the input scene parameters is then performed. The new model is validated on two different TerraSAR-X images acquired in November 2012 over the Solent area in the U.K.: the RCS relevant to several isolated ships is measured and compared with the expected value deriving from the theoretical model here introduced. Results are widely discussed and ranges of applicability finally suggested.
... A solution should be developed for this problem in the future. Besides, there are many efficient ship detection methods using multi-polarization data [3,[34][35][36]. Though this paper focuses on the single polarization channel imagery, it will exploit more polarization channels in the future. ...
... the future. Besides, there are many efficient ship detection methods using multi-polarization data [3,[34][35][36]. Though this paper focuses on the single polarization channel imagery, it will exploit more polarization channels in the future. ...
Article
Full-text available
With the rapid development of spaceborne synthetic aperture radar (SAR) and the increasing need of ship detection, research on adaptive ship detection in spaceborne SAR imagery is of great importance. Focusing on practical problems of ship detection, this paper presents a highly adaptive ship detection scheme for spaceborne SAR imagery. It is able to process a wide range of sensors, imaging modes and resolutions. Two main stages are identified in this paper, namely: ship candidate detection and ship discrimination. Firstly, this paper proposes an adaptive land masking method using ship size and pixel size. Secondly, taking into account the imaging mode, incidence angle, and polarization channel of SAR imagery, it implements adaptive ship candidate detection in spaceborne SAR imagery by applying different strategies to different resolution SAR images. Finally, aiming at different types of typical false alarms, this paper proposes a comprehensive ship discrimination method in spaceborne SAR imagery based on confidence level and complexity analysis. Experimental results based on RADARSAT-1, RADARSAT-2, TerraSAR-X, RS-1, and RS-3 images demonstrate that the adaptive scheme proposed in this paper is able to detect ship targets in a fast, efficient and robust way.
... Although the dominant backscatter is single-bounce surface scattering, PolSAR can also be applicable to deep waters such as ship E.-S. Won detection, and estimation of wind speed, ocean surface slopes, and wave spectra [6]- [9]. Laver (Porphyra), rich in protein, dietary fiber, and vitamins, is an edible algae and also a source of mineral extracts for food and medical industries. ...
Article
This letter describes a technique of extracting and estimating the underwater laver cultivation nets by using the entropy analysis of polarimetric synthetic aperture radar (PolSAR) data. The cultivation nets are placed at 10-20 cm below the sea surface, so that the Bragg waves responsible for L-band radar backscatter do not fully develop in this area of effectively shallow water. Consequently, the surface becomes smooth, and the backscatter radar cross section (RCS) becomes small in comparison with that from deep water without cultivation nets. If RCS from the cultivation area is at the system noise level, the image can be considered as arising from a random process, and the polarimetric entropy should be higher than the open sea area where the radar backscatter is dominated by the single-bounce surface scattering process. We will show that, using the data acquired by Phased Array L-band SAR onboard the Advanced Land Observing Satellite over the Tokyo Bay, Japan, the polarimetric entropy is an effective means of extracting underwater cultivation areas in comparison with the amplitude images. The area of the laver cultivation is then estimated by applying a constant false alarm rate to the entropy images to yield good agreement with the ground-truth data.
... The CCRS airborne SAR system [1,2] was transferred to Environment Canada in 1996 and is owned and operated by the Emergency Science Division there. CCRS and DND (Department of National Defense) continue to use and evaluate the facility and explore its use in a number of applications [3,4]. The system can collect SAR data in a number of modes including alongtrack and cross-track interferometry. ...
... The cross-polarisation (HV ) channel is able to provide better ROC curves compared with the co-polarisation ones (HH and V V ). This result was also observed by other researchers [1], [11], [12]. Accordingly to the Bragg model, the sea clutter has a very low (or even null) backscattering in the cross-channel, leading in many circumstances to an increased contrast. ...
... Forthcoming systems with configurations that enable the acquisition of C-band or multi-frequency quadpolarized data are expected to extend the potential for ship detection and identification (e.g. Touzi, 1999). Ship detection is a striking example of the type of applications that will benefit most from the enhanced spatial resolutions of satellites like RADARSAT-2. ...
Article
Full-text available
To date, space-borne SAR data have been widely available from single channel, that is, single frequency and single polarization, radar systems. In the near future, we expect SAR satellites with enhanced capabilities in terms of polarization, frequency, spatial resolution, spatial coverage and temporal resolution. In this paper, we will introduce some of the satellites planned and deliberate upon the increase in applications potential resulting from the progress in SAR technology. The application fields discussed are agriculture, forestry, geology, hydrology, oceans, and sea ice. Most applications are anticipated to benefit from the upcoming availability of cross-polarized C-band data. Likewise the introduction of fully polarimetric C-band satellites and multi-frequency satellites is expected to improve the overall application potential.
... In the literature, several papers have described ship detection using radar polarimetry [4][5][6][7], however the technique proposed here is entirely innovative since it makes use of a methodology introduced by the authors in [1][2][3]. The proposed detector will be referred to as a notch filter since the detector rejects the target selected (in our case the sea) and detects anything different from sea. ...
Article
Full-text available
Target detection of marine feature is a major topic for the security and monitoring of coastlines. Synthetic Aperture Radar (SAR) has been shown to be particularly useful for this application because of its all-weather and night capability. In this paper a new ship and iceberg detection methodology is described that makes novel use of the polarimetric representation of targets contained in SAR data. This polarimetric representation can be characterized by a vector with an algebraic formalism in a multi-dimensional complex space. The algorithm proposed is based on a perturbation analysis in the target space recently developed and published by the authors [1-3], which was focused on land based target detection. In this new work, the general target detector is optimised for detection of marine features like ships or icebergs. The algorithm can be considered to be a negative filter focused on sea. Consequently, all the features which have a polarimetric behaviour different from the sea are detected and considered as targets. Testing with RADARSAT-2 full polarimetric data shows significant agreement with the expected location of ships, boats and buoys, moreover the detection seems to be independent on the sea state. Further validation exercises are planned where SAR data will be acquired over regions containing ships with GPS location trackers.
... Their results show that the mean backscattering coefficient of fishponds is slightly higher on C-band images acquired in VV polarization than in HH. VV data are, however, more sensitive to sea surface roughness (Touzi, 1999) which in turn depends on wind speed. Wind speeds greater than approximately 1.5 m/s (Fingas and Brown, 2000) create waves that increase the return signal intensity in C-band, diminishing the contrast among sea surface and the structures located offshore. ...
Technical Report
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Inventory and monitoring of coastal aquaculture and fisheries structures provide important baseline data for decision-making in planning and development, including regulatory laws, environmental protection and revenue collection. Mapping these structures can be performed with good accuracy and at regular intervals by satellite remote sensing, which allows observation of vast areas, often of difficult accessibility, at a fraction of the cost of traditional surveys. Satellite imaging radar (SAR) data are unique for this task not only for their inherent all-weather capabilities, very important as aquaculture activities mainly occur in tropical and subtropical areas, but essentially because the backscatter from the structure components allows for their identification and separation from other features. The area selected and object of the study has been Lingayen Gulf, sited in Northwestern Luzon Island, the Philippines, where all these structures of interest occur. Field verification of the methodology resulted in the following accuracy: fishponds 95 percent, fish pens 100 percent. Mapping accuracy for fish cages was estimated at 90 percent and for fish traps at 70 percent. The study is based on interpretation of SAR satellite data and a detailed image analysis procedure is described. The report aims at the necessary technology transfer for an operational use of the approach indicated in other similar environments.
... The proposed concept could exploit an additional polarization (dual-pol) to improve the detection performance [43] - [50]. The improved performance, however, comes at the expense of an increased complexity and cost. ...
Article
Full-text available
This paper addresses the design of a low-cost synthetic aperture radar (SAR) for a single dedicated application, namely illegal vessel detection, which can be implemented using a small satellite and is characterized by reduced transmit power and high resolution. Minimum requirements in terms of noise-equivalent sigma zero and resolution that ensure acceptable detection performance are derived based on ship statistics extracted from TerraSAR-X data. One peculiarity of the design is that a pulse repetition frequency much smaller than the nominal Doppler bandwidth is selected to increase the swath width beyond the classical SAR limitation without using digital beamforming, as azimuth ambiguities can be tolerated for this specific application. Several design examples of SAR systems operating in X band demonstrate the potential of this concept for small ship monitoring over swaths of 50-90 km with antennas smaller than 0.6 m2 and very low average transmit powers comprised between 20 and 80 W.
... In addition, the polarimetric entropy H is extracted from dual-polarimetric covariance matrix and used as a comparison parameter. A ship detector based on the entropy H retrieved from full-polarimetric airborne SAR data was first proposed in [28]. ...
Article
The Sentinel-1A is the first of two satellites that composes the Sentinel-1 radar mission. Both satellites operate a C-band synthetic aperture radar (SAR) system to give continuity to the European SAR program. SAR is a flexible sensor able to fulfil users/applications requirements in terms of resolution and coverage thanks to different operational modes and polarizations.With the in-orbit availability of very-high-resolution X-band SAR sensors, the Sentinel-1 satellites have been designed to achieve wide coverage at medium to high resolution. The interferometric wide swath (IWS) mode implemented with the terrain observation with progressive scan (TOPS) technique is the standard acquisition mode over European waters and land masses. IWS in dual-polarization (VV/VH) combination offers 250-km swath at 5 m × 20 m (range × azimuth) spatial resolution. These specifications are in line with the needs of the European Maritime and Security Agency (EMSA) for oil spill and ship detection applications included in the CleanSeaNet program. The main goals of this paper are: assessment of medium-tohigh- resolution C-band Sentinel-1 data with very-high-resolution X-band TerraSAR-X data for maritime targets detection; synergetic use of multiplatforms satellite SAR data for target features extraction; evaluation of polarimetric target detectors for the available co-polarization and cross-polarization Sentinel-1A IWS VV/VH products. The objectives are achieved by means of real, almost coincident C-band and X-band SAR data acquired by Sentinel-1A and TerraSAR-X satellites over Gulf of Naples and Catania (South Italy). Furthermore, the obtained results are supported by recorded ground truth vessel reports via terrestrial automatic identification system (AIS) stations located in the area.
... Circular polarised SAR has received more attention. It has been applied to ocean monitoring systems in various countries [6,7]. This paper compares the imaging results of circular polarised SAR and linear polarised SAR under heavy sea conditions and evaluates the suppression effects to sea waves by polarisations. ...
Article
Full-text available
Multi-polarisation synthetic aperture radar (SAR) imaging simulation of ship under heavy sea condition is presented here. Full-wave method is used to compute the fully polarimetric backscattered waves of the complex scene of ship and sea surface. The influence by heavy sea on SAR imaging results is investigated; furthermore, the suppression effects to sea waves by different polarisations are evaluated in detail.
... It represents more detailed information about the target backscattering in various polarization bases and thus can be advantageous for target characterization. The PS technique has been widely used to characterize point and distributed targets [3][4][5] including diverse applications viz., land cover feature extraction, crop classification, etc. [6,7]. ...
... Man-made target detection from polarimetric SAR data has been widely used in many applications, such as disaster assessment, city change detection, and military target surveillance [6]. For instance, several methods based on physical mechanisms have been applied to polarimetric SAR image data for ship detection [7] [8] [9]. ...
Article
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Detection of man-made targets using polarimetric synthetic aperture radar (PolSAR) data has become a promising research area. The reflection symmetry is gradually being applied to man-made target detection algorithms as a physical property that can distinguish between man-made targets and natural clutter. However, the two terms related to the reflection symmetry property in the polarimetric coherency matrix, namely, the 12C and 23C terms, are not fully exploited by the traditional methods. To fully exploit the polarization information of the two terms, an image fusion strategy based on the position and scale information of the scale-invariant feature transform (SIFT) key points is proposed in this paper. Then, a new Wishart classifier based on the patch-level Wishart distance is used to realize automatic target detection of the fused image. The experimental results on measured data show that the proposed method can enhance the contrast between targets and clutter. In addition, the detection performance of the proposed method under different target-to-clutter ratios (TCRs) are verified on the synthetic data and measured data.
... As X pq LR 0, the preferred direction for the two changes tends to ς = 0 and ς = π, respectively. These changes may occur when large targets appear on the sea (e.g., ships) [40] or when there is a growth of large vegetation [41]. The variation of multiple target parameters may occur for complex changes and depends on collateral conditions. ...
Article
Change detection (CD) is a crucial topic in many remote sensing applications. In the recent years, satellite polarimetric synthetic aperture radar (PolSAR) systems (e.g., the Sentinel-1 constellation) became a suitable tool for multitemporal monitoring due to the regular acquisitions with a short revisit time in different polarimetric channels. Methods for CD in PolSAR data mainly focus on binary CD (i.e., they provide information about the presence/absence of change only), whereas the polarimetric enhanced information provides multiple features that can be exploited for performing multiclass CD. In this article, we introduce a novel framework for the characterization of multitemporal changes in dual-polarimetric data. The framework is based on the definition of polarimetric change vectors (PCVs) and their representation in a polar coordinate system. PCVs allow characterizing and, thus, to separate multiclass changes in terms of target properties of the single-time scenes and the scattering theory. The proposed model is used to: 1) derive the statistical behaviors of change and no change classes in PolSAR multitemporal images; 2) design an automatic and unsupervised strategy to estimate the optimal number of changes; and 3) distinguish no change from change classes and the kinds of change from each other. An experimental analysis has been conducted on three multitemporal PolSAR data sets having different complexities in terms of number and kinds of change classes. The results confirm the effectiveness of the proposed approach and the better performance with respect to both specific techniques for CD in dual-pol SAR data and a general multiclass CD method, not designed for PolSAR data.
... In addition, SAR polarimetry provides significant information for ship detection. Compared against the co-polarized channels (HH or VV), a substantial improvement is observed when using the cross-polarized channel (HV) [29]. Generally, since it had been shown that QP SAR provides the best ship detection performance [30], polarimetric properties of ships have been employed for ship detection [31,32]. ...
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Compact polarimetric synthetic aperture radar (CP SAR), as a new technique or observation system, has attracted much attention in recent years. Compared with quad-polarization SAR (QP SAR), CP SAR provides an observation with a wider swath, while, compared with linear dual-polarization SAR, retains more polarization information in observations. These characteristics make CP SAR a useful tool in marine environmental applications. Previous studies showed the potential of CP SAR images for ship detection. However, false alarms, caused by ocean clutter and the lack of detailed information about ships, largely hinder traditional methods from feature selection for ship discrimination. In this paper, a segmentation method designed specifically for ship detection from CP SAR images is proposed. The pixel-wise detection is based on a fully convolutional network (i.e., U-Net). In particular, three classes (ship, land, and sea) were considered in the classification scheme. To extract features, a series of down-samplings with several convolutions were employed. Then, to generate classifications, deep semantic and shallow high-resolution features were used in up-sampling. Experiments on several CP SAR images simulated from Gaofen-3 QP SAR images demonstrate the effectiveness of the proposed method. Compared with Faster RCNN (region-based convolutional neural network), which is considered a popular and effective deep learning network for object detection, the newly proposed method, with precision and recall greater than 90% and a F 1 score of 0.912, performs better at ship detection. Additionally, findings verify the advantages of the CP configuration compared with single polarization and linear dual-polarization.
... Additionally, various studies on wake detection based on frequency have shown that ships and wakes are more easily imaged in X-band SAR data than C-band data [7], [8]. One study that utilized polarization showed that among HH, VV, and HV, HH polarization provides the best ship-sea contrast [9]. The performance of ship detection using polarimetry SAR data has also been compared with that obtained from single-channel SAR data [10]. ...
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Accurately tracking marine traffic considering security and commercial activities is still challenging despite its increasing global importance. Recently, space-borne synthetic aperture radar (SAR) is being considered to accurately monitor maritime traffic, and techniques to detect the position of ships and estimate their velocity have become essential. Here, we investigated the potential for automatic estimation of ship velocity using the azimuth offset between ships and wakes detected using convolutional neural network (CNN) coupled with SAR imagery. We found that azimuth offset is proportional to the Doppler shift effect of the back-scattered signal in SAR, thus, it relates to the radial velocity of a moving target. Consequently, we propose a method whereby a CNN is applied to automatically detect ship wakes from TanDEM-X data. In this method, ship velocity is calculated using the azimuthal distance (i.e., azimuth offset) between the stern of the detected ship and the vertex of the detected V-shape wake—determined as the intersection of two lines obtained through edge filtering and Radon transforms. The location and number of detected ships are then compared with an automatic identification system (AIS), and the calculated velocity of the ship is compared with the velocity obtained via along-track interferometry and AIS. Results show that our method automatically detects ships and wakes with accuracies of 91.0% and 93.2%, respectively, and estimates the velocity of ships with an accuracy of 0.13 m/s. This method is effective when wind velocities are not substantially higher than 5.5 m/s and ship velocities are not extremely low.
... Given the strong radar return signal from ships it follows that the ship / sea backscatter contrast and the ship detection potential are highest in C-HV images. Forthcoming systems with configurations that enable the acquisition of C-band or multifrequency quad-polarized data are expected to extend the potential for ship detection and identification (e.g. [11]). Ship detection is a striking example of the type of applications that will benefit most from the enhanced spatial resolutions of satellite systems like RADARSAT-2. ...
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Ship detection with Synthetic Aperture Radar (SAR) is a major topic for the security and monitoring of maritime areas. One of the advantages of using SAR lays in its capability to acquire useful images with any-weather conditions and at night time. Specifically, this paper proposes a new methodology exploiting polarimetric acquisitions (dual- and quad-polarimetric). The methodology adopted for the detector algorithm was introduced by the author and performs a perturbation analysis in space of polarimetric targets checking for coherence between the target to detect and its perturbed version on the data. In the present work, this methodology is optimized for detection of marine features. In the end, the algorithm can be considered to be a negative (notch) filter focused on sea. Consequently, all the features which have a polarimetric behavior different from the sea are detected (i.e., ships, icebergs, buoys, etc). Moreover, a dual polarimetric version of the detector is designed, to be exploited in the circumstances where quad polarimetric data cannot be acquired. The detector was tested with TerraSAR-X quad polarimetric data showing significant agreement with the available ground truth. Moreover, the theoretical performances of the detector are tested with Monte Carlo simulations in order to extract the probabilities of detection and false alarm. An important result is that the detector is, up to some extend, independent of the sea conditions.
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Detection of icebergs is a major topic for surveillance of polar maritime areas and coastlines. Synthetic Aperture Radar (SAR) has been shown to be particularly useful because of its all-weather and night capability. In this paper a methodology based on the polarimetric perturbation analysis is presented. The algorithm can be considered to be a negative filter focused on sea. Consequently, all the features which have a polarimetric behavior different from the sea are detected and considered as targets (i.e. ships, buoys, icebergs). In this work the notch filter is focused on icebergs detection. A test with TerraSAR-X quad polarimetric data was performed over a scene acquired on the Canadian coastal area (Northwest Passages). The detections showed promising results, with identification of areas where large and small icebergs appear, but also ridges seems to be detected.
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Ship–sea contrast can be improved significantly when the full polarimetric information is used, compared with the information provided by a single polarization channel. Therefore, a new automatic ship detection method, termed SPAN Wishart (SPWH), is proposed in this paper based on an unsupervised classification concept, which combines the SPAN of a polarimetric SAR (POLSAR) data with the complex Wishart classifier. The significant improvement of this technique is to utilize the SPAN of ship cluster center as an iterative termination criterion to realize the automatic ship detection. Then, another method based on multifrequency is proposed to discriminate between ships and their ambiguities to provide a substitute for the ground truth for the subsequent validation of the SPWH algorithm by using an AIRSAR polarimetric dataset, which consists of $C$ - and $L$ -band data covering Kojimawan in Tamano of Japan. After that, the SPWH is validated only using the $L$ -band data with the defined ships by comparing the performance of the SPWH with a traditional CFAR detector. By contrast, the SPWH algorithm is more effective, robust, and completely automatic.
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Ship detection is an important topic in remote sensing, and synthetic aperture radar (SAR) has a valuable contribution, allowing detection at nighttime and with almost any weather conditions. In addition, polarimetry can play a significant role considering its capability to discriminate between different targets. Recently, a new ship detector exploiting polarimetric information has been developed, namely, the Geometrical Perturbation–Polarimetric Notch Filter (GP–PNF). This work is focused on devising two statistical tests for the GP–PNF. The latter allow an automatic and adaptive selection of the detector threshold. Initially, the probability density function (pdf) of the detector is analytically derived. Finally, the Neyman–Pearson lemma is exploited to set the threshold calculating probabilities using the clutter pdf (i.e., a constant false-alarm rate) and a likelihood ratio. The goodness of fit of the clutter pdf is tested with four real SAR data sets acquired by the RADARSAT-2 and the TanDEM-X satellites. The former images are quad-polarimetric, whereas the latter are dual-polarimetric HH/VV. The data are accompanied by the Automatic Identification System (AIS) location of vessels, which facilitates the validation of the detection masks. It can be observed that the pdfs fit the data histograms, and they pass the two sample Kolmogorov–Smirnov and $chi^2$ tests.
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The scattered wave is represented in terms of two independent and rotation invariant parameters: the degree of polarization (DoP) and the total scattered intensity . The scattered wave polarization signature is introduced as a convenient graphical representation of the variations of the two scattered wave observable parameters as a function of the transmitting antenna polarization. It is shown that the signature of the DoP and the total scattered intensity provide information on ocean and ship scattering that is complementary to that provided by the conventional received wave intensity polarization signature. While polarization signature of the ocean's Bragg scattering is sensitive to wind speed and synthetic aperture radar illumination angle, the DoP polarization signature appears to depend mainly on ocean surface roughness. The large dynamic range and low pedestal height of ship DoP polarization signature, in comparison with that of the ocean, favors the use of DoP for ship detection in comparison with . Optimization of the scattered wave parameters appears to be a convenient tool for efficient ship detection. The scattered wave optimization technique introduced by R. Touzi et al. in the nineties, is reconsidered and applied for enhanced ship detection. It is shown that the excursion of DoP, , and the minimum DoP, , permits a significant improvement in ship-sea contrast in comparison with conventional (i.e., scalar) single channel polarizations (HH, VV, and HV). Th- additional information provided by the maximum DoP, solves for ship ambiguities with land targets. Quantification of the ship-ocean contrast is reconsidered in the context of nonstationary ship signal. The ship peak signal quantification appears to be the most suitable method for accurate measurement of ship-ocean contrast in the presence of a nonstationary ship signal. The local performs better than the peak of and single polarizations (HH, VV, and HV) . The added value of polarimetric RS2 information for ship detection is demonstrated using wide swath (50 km) polarimetric RADARSAT-2 data collected at 29° and 40° incidence angle over vessels (validated with Automatic Identification System data) in the Strait of Georgia, near Vancouver, Canada.
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Synthetic aperture radar plays a vital role in ship detection due to the possibility of acquiring high-resolution images at nighttime and under cloud cover. This letter is focused on improving ship detection, exploiting the capability of TanDEM-X to collect interferometric data. Currently, along-track interferometry is used to estimate the speed of ocean surface currents or vessels. The detection of ships plays an important role in the retrieval of vessel speed and is mostly executed exploiting only one of the TanDEM-X images (i.e., not taking advantage of the availability of a second interferometric image). The aim of this study is to extend the capabilities of a ship detector previously developed by the authors, namely, geometrical perturbation-polarimetric notch filter (GP-PNF), to include single-pass interferometric information acquired by TanDEM-X. Interestingly, such enhancement makes it possible to employ the GP-PNF with single-polarization data as well. The proposed algorithms and their statistical behavior are tested on five Tandem-X dual-polarimetric HH/VV scenes acquired in the North Sea. The detection results are validated, exploiting the Automatic Identification System location of vessels. All of the new GP-PNF versions show good performance and provide larger vessel-sea contrast compared with single-channel detectors.
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The RADARSAT Constellation Mission (RCM), which involves three small synthetic aperture radar (SAR) satellites flying in a constellation configuration, will be equipped with fully polarimetric (FP) capabilities in addition to single-polarization (HH, HV, VV), conventional (HH-HV, VV-VH, and HH-VV), and hybrid (i.e., compact) dual polarization. In this article, the added value of polarimetric SAR information for enhanced ship detection is demonstrated using polarimetric RADARSAT-2 (RS2) data collected over vessels (validated with Automatic Identification System (AIS) data) in the Strait of Georgia, near Vancouver, Canada. It is shown that the excursion (Δp) of the degree of polarization (DoP) provides a significant increase in ship–sea contrast in comparison with conventional (i.e., scalar) single-channel polarizations (HH, HV, VV) and compact. Δp, which is a measure of the variation of the DoP with transmit antenna polarization, performs better than compact intensities and degree of depolarization (DoD) promoted recently for ship detection. The unique potential of FP for ship classification is also demonstrated using polarimetric Convair-580 SAR data collected off Cape Race, Newfoundland, Canada. An efficient combination of successive wide-swath ScanSAR and FP, which exploits the RCM rapid-revisit capability at high latitudes, is considered for operational ship detection and classification.Résumé. La mission de la Constellation RADARSAT (MCR), qui est constituée de trois petits satellites SAR évoluant en configuration de constellation, sera équipée avec des capacités de polarisation en quadrature (FP) en plus de la polarisation simple (HH, HV, VV), de la polarisation classique (HH-HV, VV-VH, et HH-VV) et de la bipolarisation hybride (c.-à-d., compacte). Dans cet article, la valeur ajoutée des informations polarimétriques SAR pour améliorer la détection de navires est démontrée en utilisant des données polarimétriques RADARSAT-2 (RS2) recueillies sur des navires (validées avec le système d'identification automatique (AIS) de données) dans le détroit de Georgia, près de Vancouver (Canada). Il apparait que la différence (delta p) du degré de polarisation (DOP) fournit une augmentation significative du contraste entre le navire et l'eau par rapport à des polarisations simples classiques (p.ex., scalaire) (HH, HV, VV) et compactes. Le delta p, qui est une mesure de la variation de la polarisation DoP avec l'antenne d'émission, est plus performant que les intensités compactes et le degré de dépolarisation (DoD) promus récemment pour la détection de navires. Le potentiel unique de la FP pour la classification de navires est également démontré en utilisant les données polarimétriques Convair-580 SAR recueillies au large du cap Race à Terre-Neuve (Canada). Une combinaison efficace de la large fauchée ScanSAR consécutive à la FP, qui exploite la capacité de revisite rapide de la MCR dans les hautes latitudes, est considérée pour la détection et la classification opérationnelles de navires.
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Icebergs represent hazards to maritime traffic and offshore operations. Satellite synthetic aperture radar (SAR) is very valuable for the observation of polar regions, and extensive work was already carried out on detection and tracking of large icebergs. However, the identification of small icebergs is still challenging especially when these are embedded in sea ice. In this paper, a new detector is proposed based on incoherent dual-polarization SAR images. The algorithm considers the limited extension of small icebergs, which are supposed to have a stronger cross-polarization and higher cross- over copolarization ratio compared to the surrounding sea or sea ice background. The new detector is tested with two satellite systems. First, RADARSAT-2 quad-polarimetric images are analyzed to evaluate the effects of high-resolution data. Subsequently, a more exhaustive analysis is carried out using dual-polarization ground-detected Sentinel-1a extra wide swath images acquired over the time span of two months. The test areas are in the east coast of Greenland, where several icebergs have been observed. A quantitative analysis and a comparison with a detector using only the cross-polarization channel are carried out, exploiting grounded icebergs as test targets. The proposed methodology improves the contrast between icebergs and sea ice clutter by up to 75 times. This returns an improved probability of detection.
Conference Paper
In this work we investigate radar imaging satellites' dependency on ground stations to transfer the image data. Since synthetic aperture radar images are very big, only ground stations are equipped to process that much data in realtime. This is a problem for maritime surveillance as it creates delay between imaging and processing. We propose a hardware algorithm that can be used by a satellite to detect ships and extract information about them in real time, and since this information is smaller it can be relayed with significant reduction in delay. For ship detection, adaptive thresholding algorithm with exponential model is used. This algorithm was selected as it can be applied in real time. For the property calculation, a data accumulating, single-look, connected component labeling algorithm is proposed. This algorithm accumulates data about the connected components which is then used to calculate the properties of ships using image moments. The combined algorithm was then validated on RADARSAT-2 images using Matlab for software and co-simulation for hardware. The algorithm was able to detect ships and calculate the features with less than 5% error.
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Most of the recent research in the field of marine target detection has been concentrating on ships with large metallic parts. The focus of this work is on much more challenging targets represented by small rubber inflatables. They are of importance, since in recent years they have largely been used by migrants to cross the Mediterranean Sea between Libya and Europe. The motivation of this research is to mitigate the ongoing humanitarian crisis at Europe’s southern borders. These boats, packed with up to 200 people, are in no way suitable to cross the Mediterranean Sea or any other big water body and are in distress from the moment of departure. The establishment of a satellite-based surveillance infrastructure could considerably support search and rescue missions in the Mediterranean Sea, reduce the number of such boats being missed and mitigate the ongoing death in the open ocean. In this work we describe and analyze data from the InflateSAR acquisition campaign, wherein we gathered multiple-platform SAR imagery of an original refugee inflatable. The test site for this campaign is a lake which provides background clutter that is more predictable. The analysis considered a sum of experiments, enabling investigations of a broad range of scene settings, such as the vessel’s orientation, superstructures and speed. We assess their impact on the detectability of the chosen target under different sensor parameters, such as polarimetry, resolution and incidence angle. Results show that TerraSAR-X Spotlight and Stripmap modes offer good capabilities to potentially detect those types of boats in distress. Low incidence angles and cross-polarization decrease the chance of a successful identification, whereas a fully occupied inflatable, orthogonally oriented to the line of sight, seems to be better visible than an empty one. The polarimetric analyses prove the vessel’s different polarimetric behavior in comparison with the water surface, especially when it comes to entropy. The analysis considered state-of-the-art methodologies with single polarization and dual polarization channels. Finally, different metrics are used to discuss whether and to which extent the results are applicable to other open ocean datasets. This paper does not introduce any vessel detection or classification algorithm from SAR images. Rather, its results aim at paving the way to the design and the development of a specially tailored detection algorithm for small rubber inflatables.
Conference Paper
The development of radar polarimetry and radar interferometry is advancing rapidly. Whereas with radar polarimetry the textural fine-structure, target orientation, symmetries and material constituents can be recovered with considerable improvement above that of standard “amplitude-only” radar, with radar interferometry the spatial (in depth) structure can be explored. In “polarimetric interferometric synthetic aperture radar (POL-IN-SAR) imaging”, it is possible to recover such co-registered textural and spatial information from POL-IN-SAR digital image data sets simultaneously, including the extraction of digital elevation maps (DEM) from either polarimetric (scattering matrix) or interferometric (single platform: dual antenna) SAR systems. Simultaneous polarimetric-plus-interferometric SAR offers the additional benefit of obtaining co-registered textural-plus-spatial three-dimensional POL-IN-DEM information, which, when applied to repeat-pass image-overlay interferometry, provides differential background validation, stress assessment and environmental stress-change information with high accuracy. Then, either designing “multiple dual-polarization antenna POL-IN-SAR” systems or applying advanced “POL-IN-SAR image compression techniques” will result in “POLarimetric TOMOgraphic (multi-interferometric) SAR” or “POL-TOMO-SAR” imaging. This is of direct relevance to wide-area, dynamic battle-space surveillance and local-to-global environmental background validation, stress assessment and stress-change monitoring of terrestrial and planetary surface covers
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A statistical approach to point target detection in a clutter background is used to delineate the expected performance of the RADARSAT SAR (C-band HH polarization) for ship detection, and to compare the expected ship detection performance for the various RADARSAT SAR beam modes. Smaller ships may be detected with decreasing wind speed, increasing incidence angle, and finer resolution. ScanSAR Narrow Far is expected to be a good compromise between spatial coverage and detection probability. We present a quantitative validation of these model predictions based upon data acquired during a RADARSAT SAR ship detection/validation field program, which was held in March/April 1996 off the coast of Halifax, Nova Scotia. The program included buoy measurements of wind and wave conditions and RADARSAT SAR passes with known ships in each scene. We present validation of some of the model's key assumptions, in particular those concerning our hybrid C-band HH polarization ocean cross-section model, image probability density function, and ship radar signatures.
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Radar polarimetry theory is reviewed, and comparison between theory and experimental results obtained with an imaging radar polarimeter employing two orthogonally polarized antennas is made. Knowledge of the scattering matrix permits calculation of the scattering cross section of a scatterer for any transmit and receive polarization combination, and a new way of displaying the resulting scattering cross section as a function of polarization is introduced. Examples of polarization signatures are presented for several theoretical models of surface scattering, and these signatures are compared with experimentally measured polarization signatures. The coefficient of variation, derived from the polarization signature, may provide information regarding the amount of variation in scattering properties for a given area.
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An automatic ship and ship wake detection system for spaceborne SAR images is described and assessed. The system is designed for coastal regions with eddies, fronts, waves and swells. The system uses digital terrain models to simulate synthetic SAR images to mask out land areas. Then a search for ship targets is performed followed by wake search around detected ship candidates. Finally, a homogeneity test and wake behavior test are performed which reduces the number of false alarms substantially. The system is demonstrated with ERS-1 SAR images and its performance is assessed using Seasat and ERS-1 images. No other information about the ships was available, hence, the basis for the assessment is through comparison with human visual interpretation of the same data. The number of lost ships (ship-like targets) was 7-8% for both Seasat-A and ERS-1. No false ships were detected. The number of lost or false wakes (wake-like features) was higher in ERS-1 images than in Seasat-A images and was nearly 15%. Taking into account the extremely strong variations in sea state in some of the selected scenes, the automatic detection performance is considered to be very good. In addition, the requirement of analyzing a 3-look ERS-1 scene of 100 km×100 km in less than eight minutes has been achieved on a workstation
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A general polarimetric model for orbital and Earth synthetic aperture radar (SAR) systems that explicitly includes key radar architecture elements and is not dependent on the reciprocity assumption is developed. The model includes systems whose receiving configuration is independent of the transmitted polarization (one configuration), as well as systems with two distinct receiving configurations, depending on the commanded transmitted polarization (H or V). Parameters that are independent of target illumination angle and those with illumination angle dependence are considered separately, allowing calibration approaches which are valid for targets at different illumination angles. The calibration methods presented make use of the model linearity to provide tests for the radar model accuracy and for SAR data quality. X-band polarimetric SAR are used to validate the theory and illustrate the calibration approach. The extension of the model and calibration method to other radar systems is discussed
Development of the polarimetric contrast enhancement optimization procedure and its application to sea surface scatter in POL-SAR image analysis
  • W M Boerner
  • M Walther
  • A C Segal
Scene descriptions for CV-580 SAR acquisitions St Magaret's Bay area
  • R K Hawkins
  • P Vachon
  • J Cranton
  • K Murnaghan
Calibration of the polarimetric Convair-580 C-band SAR
  • R Touzi
  • S Nedelcu