Philippe Bolon

Unsupervised Spatiotemporal Mining of Satellite Image Time Series Using Grouped Frequent Sequential Patterns

An important aspect of satellite image time series is the simultaneous access to spatial and temporal information. Various tools allow end users to interpret these data without having to browse the whole data set. In this paper, we intend to extract, in an unsupervised way, temporal evolutions at the pixel level and select those covering at least a minimum surface and having a high connectivity measure. To manage the huge amount of data and the large number of potential temporal evolutions, a new approach based on data-mining techniques is presented. We have developed a frequent sequential pattern extraction method adapted to that spatiotemporal context. A successful application to crop monitoring involving optical data is described. Another application to crustal deformation monitoring using synthetic aperture radar images gives an indication about the generic nature of the proposed approach.

Combining Airborne Photographs and Spaceborne SAR Data to Monitor Temperate Glaciers: Potentials and Limits

Monitoring temperate glacier activity has become more and more necessary for economical and security reasons and as an indicator of the local effects of global climate change. Remote sensing data provide useful information on such complex geophysical objects, but they require specific processing techniques to cope with the difficult context of moving and changing features in high-relief areas. This paper presents the first results of a project involving four laboratories developing and combining specific methods to extract information from optical and synthetic aperture radar (SAR) data. Two different information sources are processed, namely: 1) airborne photography and 2) spaceborne C-band SAR interferometry. The difficulties and limitations of their processing in the context of Alpine glaciers are discussed and illustrated on two glaciers located in the Mont-Blanc area. The results obtained by aerial triangulation techniques provide digital terrain models with an accuracy that is better than 30 cm, which is compatible with the computation of volume balance and useful for precise georeferencing and slope measurement updating. The results obtained by SAR differential interferometry using European Remote Sensing Satellite images show that it is possible to measure temperate glacier surface velocity fields from October to April in one-day interferograms with approximately 20-m ground sampling. This allows to derive ice surface strain rate fields required to model the glacier flow. These different measurements are complementary to results obtained during the summer from satellite optical data and ground measurements that are available only in few accessible points

Entropy as a global variable of the learning process

Abstract The work reported here is a contribution to the study of a complex motor behavior, viewed globally. The question raised is the nature of the process by which an environment-sensorimotricity coupling is organized. The material is the trajectory of a constrained free climbing task, and the main concept is entropy. The entropy of the climbers trajectory is used to measure the degree of structuring in the successive states of the subject-environment system during the learning of a complex task. It will be shown that the entropy of the trajectory decreases as learning progresses, and that the shape of the entropy curve is a function of the climbers level of expertise. A model of constraint relaxation is proposed to describe the learning process. Then, based on a theory of probabilistic inference, an attemp is made to show that this natural biological process obeys the thermodynamic laws of neural networks.

Monitoring Temperate Glacier Displacement by Multi-Temporal TerraSAR-X Images and Continuous GPS Measurements

A new generation of space-borne SAR sensors were launched in 2006-2007 with ALOS, TerraSAR-X, COSMO-Sky-Med and RadarSat-2 satellites. The data available in different bands (L, C and X bands), with High Resolution (HR) or multi-polarization modes offer new possibilities to monitor glacier displacement and surface evolution by SAR remote sensing. In this paper, the first results obtained with TerraSAR-X HR SAR image time series acquired over the temperate glaciers of the Chamonix Mont-Blanc test site are presented. This area involves well-known temperate glaciers which have been monitored and instrumented i.e. stakes for annual displacement/ablation, GPS for surface displacement and cavitometer for basal displacement, for more than 50 years. The potential of 11-day repeated X-band HR SAR data for Alpine glacier monitoring is investigated by a combined use of in situ measurements and multi-temporal images. Interpretations of HR images, analysis of interferometric pairs and performance assessments of target/texture tracking methods for glacier motion estimation are presented. The results obtained with four time series covering the Chamonix Mont-Blanc glaciers over one year show that the phase information is rarely preserved after 11 days on such glaciers, whereas the high resolution intensity information allows the main glacier features to be observed and displacement fields on the textured areas to be derived.

Watermarking by histogram specification

The paper investigates the use of image histograms as watermarks. First, the problem of exact histogram specification is addressed and a method for exact histogram specification, consistent with the human perception of brightness, is developed. Next, two watermarking techniques based on exact histogram specification are proposed. The first one directly considers image histograms as watermarks. Thus, a particular histogram is assigned as a watermark and images are further transformed to have exactly the assigned histogram. Since quite large variations in image histogram are not perceived by humans, an unlimited number of invisible watermarks can be defined for which images appear visually non-distorted. Besides, by selecting histograms which are variations of uniform histogram, the transformed images are not only uniquely marked but also enhanced. The second approach conserves, for each image, its original histogram. The watermarking procedure consists of two histogram specification transforms: a transform to the assigned watermark followed by an inverse transform to recover the original histogram. Since image recovery after a histogram specification transform is not exact, the error obtained after the two consecutive transforms is further used to track each watermark.

A statistical overview of recent literature in information fusion

The objective of this paper is to make a picture of the recent articles published on information fusion. Indeed, a great number of documents dealing with this technique are available in the literature. A classification scheme including application fields, fusion goals, fusion system architecture and mathematical tools is proposed. This overview of the last three years allows one to compute the article distribution in each class. Finally, some elements of a preliminary analysis of this classification are drawn.

Robust watermarking by histogram specification

The paper investigates the use of exact histogram specification for robust watermarking. A class of watermarks are selected such that the presence of certain groups of consecutive gray levels is considerably reduced with no visual degradation of images. The proposed technique is proven to be very resistant to many intentional and unintentional attacks.

Discrete distance operator on rectangular grids

Abstract In this paper we present a new local distance transformation adapted to rectangular grids. This situation occurs with most industrial vision systems. Such operators allow Euclidean distance transform images to be approximated by using only local operations. These operators are optimized in the context of minimizing the maximum error over circular trajectories. The formulas of the coefficients as a function of the pixel width are given in the case of a 5 × 5 neighborhood. Experimental results and comparisons with other distance operators are then presented.

Statistical and operational performance assessment of multitemporal SAR image filtering

Multitemporal synthetic aperture radar (SAR) image filtering is a useful preprocessing step for many applications that require speckle reduction. Several multitemporal filters are now available with very different characteristics. In this paper, the performance of three multitemporal filters is assessed with respect to statistical and operational criteria. Statistical criteria include measures of bias, noise reduction, and preservation of both spatial and temporal information. Operational criteria evaluate the accuracy of manual detection of geographical features such as points, lines, and surfaces. This study was carried out with the help of ten photointerpreters. It uses a set of seven multitemporal SAR images from the European Remote Sensing 1 (ERS-1) satellite. It provides guidelines to select multitemporal filters according to the application and the subsequent processing.

Application of Baddeley's distance to dissimilarity measurement between gray scale images

Abstract In this paper, we introduce a dissimilarity measure between two gray-scale images based on Baddeleys distance. To some extent, it can be regarded as a modification of that proposed by Wilson et al. [Internat. J. Comput. Vision 24 (1) (1997) 5–18]. Images are represented by surfaces in a 3D space, instead of their subgraphs. Distance calculations are performed by means of a 3D local distance operator adapted to parallelepipedic grids. No truncation effect is introduced. Properties of the new dissimilarity operator are compared to those of the Wilson–Baddeley–Owen operator in terms of sensitivity to gray level variations, spatial shifts and shape distortions. Compared with the Wilson–Baddeley–Owen operator, a more linear behavior is observed. A simplified phenomenological model is proposed in order to explain this behavior.