Azzedine Bouaraba

Robust Techniques for Coherent Change Detection Using Cosmo-Skymed SAR Images

The satellite-borne SAR (Synthetic Aperture Radar) is a quite promising tool for high-resolution geo-surface measurement. Recently, there has been a great interest in Coherent Change Detection (CCD), where the coherence between two SAR images is evaluated and analyzed to detect surface changes. The sample coherence threshold may be used to distinguish between the changed and unchanged regions in the scene. Using COSMO-SkyMed (CSK) images, we show that for changed areas, the coherence is low but not completely lost. This situation, which is caused by the presence of bias in the coherence estimate, considerably degrades the performance of the sample threshold method. To overcome this problem, robust detection in inhomogeneous data must be considered. In this work, we propose the application and improvement of three techniques: Mean Level Detector (MLD), Ordered Statistic (OS) and Censored Mean Level Detector (CMLD), all applied to coherence in order to detect surface changes. The probabilities of detection and false alarm are estimated experimentally using high-resolution CSK images. We show that the proposed method, CMLD with incorporation of guard cells (GC) in the range direction, is robust and allows for nearly 4% higher detection probability in case of low false alarm probability.

InSAR Phase Filtering via Joint Subspace Projection Method: Application in Change Detection

A new approach is presented to estimate the synthetic aperture radar (SAR) interferometric phase via the joint subspace projection. In this letter, a new formulation is proposed to transform the cost function minimization problem into the problem of finding the roots of a second-order polynomial whose coefficients are evaluated via the joint noise subspace. The proposed method enjoys a substantially reduced computational complexity and improves the estimation of the interferometric phase. Results obtained using real SAR data show the effectiveness of the proposed method. In the change detection application, the method offers much better separation between the changed and unchanged coherence pixels than existing filters.

Improving Ccd Performance by the Use of Local Fringe Frequencies

Coherent Change Detection (CCD) using multi-temporal Synthetic Aperture Radar (SAR) is one of the most important applications of remote sensing technology. With the advent of high- resolution SAR images, CCD has received a lot of attention. In CCD, the interferometric coherence between two SAR images is evaluated and analyzed to detect surface changes. Unfortunately, the sample coherence estimator is biased, especially for low-coherence values. The consequence of this bias is the apparition of highly coherent pixels inside the changed area. Within this context, the detection performance will considerably degrade, particularly when using high resolution SAR data. In this paper, we propose a new CCD method based on cleaning of coherence inside changed areas, which is characterized by high Local Fringe Frequencies (LFF) values, followed by a space-averaged coherence method. According to the proposed method, the results obtained with Cosmo-SkyMed (CSK) SAR data show an enhancement of change detection performance of about 6% while preserving subtle changes.

Combination of different SAR modalities for geospatialintelligence applications in a harbor environment

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.

Activity monitoring in a commercial harbor using multitemporal repeat-pass interferometric SAR data

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 multi-temporal spaceborne SAR data for monitoring human activity within a commercial port. A large stack of spotlight images is available for this project, allowing a high level of temporal detail. In the current paper HiRes spotlight data from the Cosmo-Skymed constellation are used. For activity monitoring on land a method was developed that combines information from interferometric coherence and amplitude information into a semi-supervised change detection and classification scheme. The activity monitoring on water focusses on the detection of ships in the harbor. The ship detection is based on an image processing chain applied on the log-intensity data.