Renaud Binet

Short-range synthetic aperture imaging at 633 nm by digital holography.

We present an active optical synthetic aperture-imaging system. A phase-step digital holographic setup is used as a wavefront sensor in the far field. The overlap of the holograms enables the estimation and compensation of their relative positions and phase with a speckle cross-correlation algorithm. Experimental results on a short-range synthetic aperture setup at 633 nm are presented that are based on 128 x 128 holograms. The synthesis is executed in one direction by means of rotation of the object. Test images show a significant gain of resolution in the synthesis direction. Processing errors are estimated through experiment. Random processing errors of a synthetic pupil composed of 33 merged holograms are negligible, but biases induced by unknown optical aberrations ofthe reference wave induce defocusing and astigmatism.

Influence of camera distortions on satellite image registration and change detection applications

Applications such as change detection and digital elevation model extraction from optical images require a rigorous modeling of the acquisition geometry. We show that the unrecorded satellite jitter during image acquisition, and the uncertainties on the CCD arrays geometry are the current major limiting factors for applications requiring high accuracy. These artifacts are identified and quantified on several optical satellites, i.e., SPOT, ASTER, QuickBird, and HiRISE.

Object oriented assessment of damage due to natural disaster using very high resolution images

A building damage assessment method applied to the case of the earthquake of Bam is proposed in this paper. It uses two very high resolution images and focuses on the footprints of the buildings. The need of an accurate registration of the buildings is demonstrated; a registration method that improved the damage assessment is proposed. It allows a classification performance of the buildings among four damage grades up to 78%. The impact of a lower accuracy of the buildings roofs segmentation is evaluated; we show that it mainly leads to a decrease of the capacity to identify the partial damage on buildings.

Quantitative Assessment Of Building Damage In Urban Area Using Very High Resolution Images

Very high resolution images are particularly well adapted to damage assessment methodology in urban area because on one hand it allows an analysis focused on the buildings solely through an object-oriented analysis, and on the other hand it permits a quantitative evaluation of this damage assessment using a visually established ground truth. We propose in this paper a method of damage assessment that uses these two benefits. First an original object oriented approach to register the images is presented. Then a simple and fast damage assessment method based on correlation is proposed and tested on the test-case of the earthquake of Bam in December 2003. Each building of a test-area is classified using Support Vector Machines. The performance of the method in each case is evaluated thanks to a manually constructed reference database that uses the European Macroseismic Scale. As a result, 75% of buildings are well classified among four different EMS damage grades.

Damage Assessment on Buildings using Multisensor Multimodal Very High Resolution Images and Ancillary Data

Satellite images are useful to prevent major disasters and mitigate their impact on populations. Their analysis is usually manually conducted by operators. Automatic processing of very high resolution (VHR) images is critical when the images to analyse are acquired with different modalities: acquisition angles, spatial resolution, or even sensor; however, this situation is frequent in an operational scope. We propose a method to assess damage on buildings using a pair of VHR images and ancillary data. We assess its robustness against the different modalities. We show that the performance of our methodology decreases with the acquisition angles difference but is robust against changes in spatial resolution and against the use of images acquired with different sensors. Even in extreme conditions, damaged buildings are well detected. Our methodology leads to a global performance from 72% with a difference angle of 80deg, to 93% for a difference angle of 24deg.

Synthetic aperture, a way to high resolution active imaging

Synthetic aperture is a way to overcome the spatial resolution limitation given by limited physical of an observation instrument. Active synthetic aperture techniques at optical wavelengths are presented. We show that 2D arrays of detectors overcome the co-phasing problem of the sub-pupils provided there is an overlap between each acquisition. This technique was applied to short range imaging at 633nm in laboratory environment, yielding to diffraction limited pupils 16 times larger than the original pupil without external measurement of the pupil phase history.

Stable Coherent Area in SAR interferometry

Synthetic aperture radar images have been a tool of interest in many land cover studies for their night and day, all weather conditions operability. The classic InSAR technique is often limited by temporal and geometrical decorrelation, especially in the context of long time series analysis. Indeed, one of the major drawback of radar images is that some surfaces such as vegetated areas have a varying backscattering coefficient over time. While two images are acquired in multipass interferometric mode, this leads to a partial or sometimes complete loss of correlation of the data. This paper deals with coherence measurements based on 83 ERS images of a large area which is particularly remarkable due to the temporal stability of its interferometric coherence. This area is located on the Serre-Poncon dam, France. Longitudinal observations based on seven years frame ERS interferograms show an expected complete loss of coherence of the scene over vegetated and mountainous areas, excepted on the Serre-Poncon dam for which coherence degree remains high despite the long time span between these acquisitions. An experimental qualitative analysis is lead on the measured coherence of this Stable Coherent Area (SCA). As classic coherence estimators are biased on small averaging windows, a specific method is thus proposed to improve the results, by measuring the global coherence of the dam. This requires a compensation of the topographic and orbital phase components.