Abstract-In

Abstract-Our framework is the synthesis of multispectral images (MS) at higher spatial resolution, which should be as close as possible to those that would have been acquired by the corresponding sensors if they had this high resolution. This synthesis is performed with the help of a high spatial but low spectral resolution image: the panchromatic (Pan) image. The fusion of the Pan and MS images is classically referred as pan-sharpening. A fused product reaches good quality only if the characteristics and differences between input images are taken into account. Dissimilarities existing between these two data sets originate from two causes-different times and different spectral bands of acquisition. Remote sensing physics should be carefully considered while designing the fusion process. Because of the complexity of physics and the large number of unknowns, authors are led to make assumptions to drive their development. Weaknesses and strengths of each reported method are raised and confronted to these physical constraints. The conclusion of this critical survey of literature is that the choice in the assumptions for the development of a method is crucial, with the risk to drastically weaken fusion performance. It is also shown that the Amélioration de la Résolution Spatiale par Injection de Structures concept prevents from introducing spectral distortion into fused products and offers a reliable framework for further developments.

-Our work deals with the assessment of the quality of multimodal images synthesized at a better spatial resolution by the means of another image having such a resolution. In absence of reference images, the current protocols recommend to degrade spatially both sets of images and to perform fusion on these two new sets, thus producing synthesized images at the original low resolution. The quality budget is drawn at this scale and it is assumed that it is close to or worse than the one, which would have been drawn at high resolution if the reference images were available. This extrapolation hypothesis is the major limitation of the application of protocols. The validity of this hypothesis is studied for 44 case studies. Several distances are selected. They are compounded into several quality budgets, each of them giving an overall idea on the quality. We analyze changes in quality budgets with scales. It is found that the extrapolation hypothesis is validated in most cases. Nevertheless, the need for further investigation is underlined.

-This paper deals with the assessment of the quality of the products resulting from the application of fusion methods, exploiting the synergy of multimodal images at a low spatial resolution and images at a higher spatial resolution but with a lower spectral content. It concentrates on the assessment of the geometrical quality through the analysis of the quality of selected contours. The first objective of our paper is to present a method for the estimation of the MTF. This method applies to excerpts of images containing long well contrasted linear features. The performance of the method is assessed by applying it to several Ikonos images and comparing the results to published works. The second objective is to demonstrate that the method may be exploited to assess the geometrical quality of the fused product.

This paper focuses on the tracking and analysis of convective clouds systems from Meteosat Second Generation images. The highly deformable nature of convective clouds, the complexity of the physic processes involved, but also the partially hidden measurements available from image data make difficult a direct use of conventional image analysis techniques for tasks of detection, tracking and characterization. In this paper, we face these issues using variational data assimilation tools. Such techniques enable to perform the estimation of an unknown state function according to a given dynamical model and to noisy and incomplete measurements. The system state we are setting in this study for the clouds representation is composed of two nested curves corresponding to the exterior frontiers of the clouds and to the interior coldest parts (core) of the convective clouds. Since no reliable simple dynamical model exists for such phenomena at the image grid scale, the dynamics on which we are relying has been directly defined from image based motion measurements and takes into account an uncertainty modeling of the curves dynamics along time. In addition to this assimilation technique, we show in appendix how each cell of the recovered clouds system can be labeled and associated to characteristic parameters (birth or death time, mean temperature, velocity, growth, etc.