Seven countries within the European Defence Agency (EDA) framework are joining effort in a four year project (2009-2013) on Detection in Urban scenario using Combined Airborne imaging Sensors (DUCAS). Data has been collected in a joint field trial including instrumentation for 3D mapping, hyperspectral and high resolution imagery together with in situ instrumentation for target, background and atmospheric characterization. Extensive analysis with respect to detection and classification has been performed. Progress in performance has been shown using combinations of hyperspectral and high spatial resolution sensors.
Very high resolution multispectral imaging reached a high level of reliability and accuracy for target detection and
classification. However, in an urban scene, the complexity is raised, making the detection and the identification of small
objects difficult. One way to overcome this difficulty is to combine spectral information with 3D data. A set of (very
high resolution) airborne multispectral image sequences was acquired over the urban area of Zeebrugge, Belgium. The
data consist of three bands in the visible (VIS) region, one band in the near infrared (NIR) range and two bands in the
mid-wave infrared (MWIR) region. Images are obtained images at a frame rate of 1/2 frame per second for the VIS and
NIR image and 2 frames per second for the MWIR bands. The sensors have a decimetric spatial resolution. The
combination of frame rate with flight altitude and speed results in a large overlap between successive images. The
current paper proposes a scheme to combine 3D information from along-track stereo, exploiting the overlap between
images on one hand and spectral information on the other hand for unsupervised detection of targets. For the extraction
of 3D information, the disparity map between different image pairs is determined automatically using an MRF-based
method. For the unsupervised target detection, an anomaly detection algorithm is applied. Different methods for inserting
the obtained 3D information into the target detection scheme are discussed.
The EDA project "Detection in Urban scenario using Combined Airborne imaging Sensors" (DUCAS) is in progress.
The aim of the project is to investigate the potential benefit of combined high spatial and spectral resolution airborne
imagery for several defense applications in the urban area. The project is taking advantage of the combined resources
from 7 contributing nations within the EDA framework. An extensive field trial has been carried out in the city of
Zeebrugge at the Belgian coast in June 2011. The Belgian armed forces contributed with platforms, weapons, personnel
(soldiers) and logistics for the trial. Ground truth measurements with respect to geometrical characteristics, optical
material properties and weather conditions were obtained in addition to hyperspectral, multispectral and high resolution
spatial imagery.
High spectral/spatial resolution sensor data are used for detection, classification, identification and tracking.
KEYWORDS: Principal component analysis, Detection and tracking algorithms, Target detection, Agriculture, Target acquisition, Data processing, Sensors, Matrices, Research management, Geography
Accurate covariance matrix estimation for high dimensional data can be a difficult problem. A good approximation of
the covariance matrix needs in most cases a prohibitively large number of pixels, i.e. pixels from a stationary section of
the image whose number is greater than several times the number of bands. Estimating the covariance matrix with a
number of pixels that is on the order of the number of bands or less will cause, not only a bad estimation of the
covariance matrix, but also a singular covariance matrix which cannot be inverted. In this article we will investigate
two methods to give a sufficient approximation for the covariance matrix while only using a small number of
neighboring pixels. The first is the Quasilocal Covariance Matrix (QLRX) that uses the variance of the global
covariance instead of the variances that are too small and cause a singular covariance. The second method is Sparse
Matrix Transform (SMT) that performs a set of K Givens rotations to estimate the covariance matrix. We will compare
results from target acquisition that are based on both of these methods.
Anomaly detection (AD) in hyperspectral data has received a lot of attention for various applications. The aim
of anomaly detection is to detect pixels in the hyperspectral data cube whose spectra differ significantly from
the background spectra. Many anomaly detectors have been proposed in literature. They differ by the way
the background is characterized and by the method used for determining the difference between the current
pixel and the background. The most well-known anomaly detector is the RX detector that calculates the
Mahalanobis distance between the pixel under test (PUT) and the background. Global RX characterizes the
background of the complete scene by a single multi-variate normal distribution. In many cases this model is not
appropriate for describing the background. For that reason a variety of other anomaly detection methods have
been developed. This paper examines three classes of anomaly detectors: sub-space methods, local methods
and segmentation-based methods. Representative examples of each class are chosen and applied on a set of
hyperspectral data with different backgrounds. The results are evaluated and compared.
Since the launch of Terrasar-X, Radarsat 2 and the Cosmo-Skymed constellation, spaceborne SAR data with
a high spatial resolution have become more readily available, allowing to monitor areas with a high level of
human activity independent of weather circumstances. The current paper investigates the use of such data for
geospatial intelligence applications in an harbor environment. The applications of interest are change detection
and activity monitoring. For the analysis a set of more than twenty datasets from the three above mentioned
satellite systems, acquired over a period of 30 days over the sea harbor of Zeebrugge in Belgium is available.
Most datasets are high-resolution spotlight mode, but some scansar and full-polarimetric data have also been
acquired. In the current paper HiRes spotlight data from the Cosmo-Skymed constellation are used for change
detection and activity monitoring in the port.
Most of the current SAR systems aquire fully polarimetric data where the obtained scattering information can
be represented by various coherent and incoherent parameters. In previous contributions we reviewed these
parameters in terms of their "utility" for landcover classification, here, we investigate their impact on several
classification algoritms. Three classifiers: the minimum-distance classifier, a multi-layer perceptron (MLP) and
one based on logistic regression (LR) were applied on an L-Band scene acquired by the E-SAR sensor. MLP
and LR were chosen because they are robust w.r.t. the data statistics. An interesting result is that MLP gives
better results on the coherent parameters while LR gives better results on the incoherent parameters.
Urban areas are rapidly changing all over the world and therefore provoke the necessity to update urban maps frequently.
Remote sensing has been used for many years to monitor these changes. The urban scene is characterized by a very high
complexity, containing objects formed from different types of man-made materials as well as natural vegetation.
Hyperspectral sensors provide the capability to map the surface materials present in the scene using their spectra and
therefore to identify the main object classes in the scene in a relatively easy manner. However ambiguities persist where
different types of objects are constructed of the same material. This is for instance the case for roads and roof covers.
Although higher-level image processing (e.g. spatial reasoning) might be able to relief some of these constraints, this
task is far from straight forward. In the current paper the authors fused information gathered using a hyperspectral sensor
with that of high-resolution polarimetric SAR data. SAR data give information about the type of scattering backscatter
from an object in the scene, its geometry and its dielectric properties. Therefore, the information obtained using the SAR
processing is complementary to that obtained using hyperspectral data. This research was applied on a dataset consisting
of hyperspectral data from the HyMAP sensor (126 channels in VIS-SWIR) and E-SAR data which consists of fullpolarimetric
L-band and dual-polarisation (HH and VV) X-band data. Two supervised classifications are used; 'Logistic
Regression' (LR) which applied to the SAR and the PolSAR data and a 'Matched Filter' which is applied to the
hyperspectral data. The results of the classification are fused in order to improve the mapping of the main classes in the
scene and were compared to a ground truth map that was constructed by combining a digital topographic map and a
vectorized cadastral map of the research area. An adequate change detection of man-made objects in urban scenes was
obtained by the fusion of features derived from SAR, PolSAR and hyperspectral data.
This paper describes a new method for classification of hyperspectral images for extracting carthographic objects. The developed method is intended as a tool for automatic map updating. The idea is to use an existing map of the region of interest as a learning set. The proposed method is based on logistic regression. Logistic regression (LR) is a supervised multi-variate statistical tool that finds an optimal combination of the input channels for distinguishing one class from all the others. LR thus results in detection images per class. These can be combined into a classification image. The LR method that is used here is a step-wise optimisation that also performs a channel selection. The results of the LR are further improved by taking into account spatial information by means of a region growing method. The parameters of the region growing are optimised for each class of interest. For each class the optimal set of parameters is determined. The method is applied on a HyMap hyperspectral image of an area in Southern Germany and the results are compared to those of classical methods. For the comparison a ground truth image was created by combining data from a cadaster map and a digital topographic map.
The presented work aims to develop new methods for exploiting the potential of future SAR satellite systems.
The current paper focuses on the detection of linear objects (e.g. roads, rivers, tree lines, etc.) in multi-frequency polarimetric SAR images. We obtained sets of polarimetric P-band and L-band and VV-polarised C- and X-band images. The images cover the same region but have a different spatial resolution. We also obtained transformation matrices that relate the slant-range coordinates to geocoded coordinates for each frequency band. The detection of linear features is performed on each of the slant-range images and the results are then geocoded and fused. In SAR images, for deciding whether a line passes through a given point, a relatively large neighbourhood has to be considered because of the speckle. Normally a set of rectangles is scanned over the image and at each point the statistics of the pixels inside the different rectangles are compared to decide whether a line is present. For single-channel data, a line detector is constructed from the Touzi edge detector. For polarimetric data, we use a multi-variate hypothesis test. Because of the difference in spatial resolution and information content of the 4 frequency bands, results are improved by fusing the individual results from the different bands. On the other, the synergy with speckle reduction is also examined. Without speckle reduction, large scanning rectangles need to be used for the line detection because of the presence of the speckle. If speckle reduction is applied prior to line detection, smaller rectangles can be used. The former approach allows to detected lines that show a lower contrast while the latter allows to find smaller details and achieves a higher spatial accuracy.
The proposed method was applied to one of the sets of images and results are shown and evaluated.
The aim of this article is to explore new methods to enhance the results of automatic interpretation of SAR images by combining images acquired from different viewing directions (multi-aspect SAR images). Using the combined information extracted from multi-aspect images allows to resolve problems of obscurance, by for instance the borders of a forest, to increase the resolution and to augment the confidence in detection as compared to detection in single images. The article focuses on high-resolution polarimetric images for the automatic interpretation of an airfield scene. Specifically for this type of images we have developed a set of new image interpretation tools such as edge detectors and bar (line) detectors, both based on multi-variate statistics. These detectors are briefly described in the article. The main part of the proposed article will focus on how the use of multi-aspect images can enhance the results of these detectors. The multi-aspect images are supposed to be accurately registered. It is thus possible to warp them into a common coordinate system. Because the spatial resolution of a SAR system is usually not the same in range and azimuth, it is sometimes better to detect objects in each image separately and fuse the results of the detection at the object level. This is particularly true for the detection and delimitation of the buildings. On the other hand, edge detectors can benefit from combined information on a pixel-level. In particular edge detectors based on multi-variate statistical methods can be applied on registered images, thus increasing the confidence level of detection and reducing the false alarm rate, by combining the information at a low level. For edge detectors we will compare results of combining the information available from multi-aspect polarimetric images at different levels. In particular we will compare the results of applying them directly to the registered image set with these obtained when applying them on each individual image and fusing the results at the object level or intermediate (edge-strength) level. Similar investigations will be presented for the bar detectors. Results will be shown on a set of polarimetric L-band images of an airfield.
The presented work aims to automatically register high-resolution polarimetric SAR images with each other and other types of images. A digital topographic map is used as an aid for the registration. SAR images are very different from visual or infrared images. The idea is to identify, for each type of image, objects present on the map and easily detectable in the image. Detecting these objects in the image and matching them between map and image provides a first registration. Several object detectors were developed for the subsequent stages of the registration. Each of these detectors is briefly described. The actual registration uses a hierarchical method. First the SAR image is converted into ground range. Then a rough registration between image and map is obtained based on the position of forests and/or built-up areas. A voting method is used to find the parameters of a simple transformation model and to match the objects between map and image. The third step finds the parameters of an affine transformation based on the objects matched by the voting method. To improve the registration, objects with low 3D structure, e.g. roads and rivers, are used. The method for detecting these in SAR images yields an incomplete results leading to ambiguities for the optimal local displacement. Optimisation methods are used to overcome this problem and yield the parameters of a global transformation model. The accuracy of the registration is now within the accuracy of the map. Once the different images are registered with the map, the results of edge detectors are used to refine the registration between them.
Automatic contour detection in SAR images is a difficult problem due to the presence of speckle. Several detectors exploiting the statistics of speckle in uniform regions have been already presented in literature. However, these were mainly applied to multi-look low-resolution imagery. This paper describes two new CFAR contour detectors for high-resolution single-look polarimetric SAR images. They are based on multi-variate statistical hypothesis tests. Failing of the test indicates the presence of an edge. A test for difference in means on log-intensity images and difference in variance on complex (SLC) images are used. Both tests take into account the interchannel covariance matrix which makes them a powerful tool for contour detection in multi-channel SAR images. Spatial correlation jeopardizes the CFAR character of the detectors. This problem is often neglected. In this paper its influence on the detectors is studied and eliminated. The localisation of detected edges is improved using a directional morphological filter. Different methods to fuse the results of the two detectors are explored and compared. Results obtained on a polarimetric L-band E-SAR image are presented. Most contours are well detected. Narrow lines on a uniform background remain undetected. Although the detector was developed to detect edges only between uniform areas, it also detects edges between textured and uniform areas.
An approach to the long range automatic detection of vehicles, using multi-sensor image sequences, is presented. The algorithm was tested on a database of six sequences, acquired under diverse operational conditions. The vehicles in the sequences can be either moving or stationary. The sensors also can be moving. The presented approach consists of two parts. The first part detects targets in single images using seven texture measurements. The values of some of the textural features at a target position will differ from those found in the background. To perform a first classification between target- and non-target pixels, linear discriminant analysis is used on one test image for each type of sensor. Because the features are closely linked to the physical properties of the sensors, the discriminant function also gives good results to the remainder of the database sequences. By applying the discriminant function to the feature space of textural parameters, a new image is created. The local maxima of this image correspond to probably target positions. To reduce the false alarm rate, any available prior knowledge about possible target size and aspect ratio is incorporated using a region growing procedure around the local maxima. The second part of the algorithm detects moving targets. First any motion of the sensor itself need to be detected. The detection is based on a comparison of the spatial cooccurrence matrix within one image and the temporal cooccurrence matrix between successive images. If sensor motion is detected, it is estimated using a multi-resolution Markov Random Field model. Available prior knowledge about the sensor motion is used to simplify the motion estimation. The motion estimate is used to warp past images onto the current one. Moving targets are detected by thresholding the difference between the original and warped images. Temporal and spatial consistency are used to reduce false alarm rate.
In this paper, an approach to the automatic detection of vehicles at long range using sequences of thermal infrared images is presented. The vehicles in the sequences can be either moving or stationary. The sensor can also be mounted on a moving platform. The target area in the images is very small, typically less than 10 pixels on target. The proposed method consists of two independent parts. The first part seeks for possible targets in individual images and then merges the results for a subsequence of images. The second part of the algorithm specifically focuses on finding moving objects in the scene.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.