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In this paper, we take into account compression by introducing a pre-processing step restituting the instrument noise. Then we propose a denoising and deconvolution step optimally parametrized since the instrument response (noise and Modulation Transfer Function) is known. We achieve better restoration than classical algorithms on satellite imagery. This improvement in image quality is shown on two kinds of application: pansharpening and 3D restitution.
For the SPOT 5 satellite, a new compromise had been chosen. The supermode principle of imagery (sampling at 2.5 meter with a pixel size of 5 meter) imp roves the resolution by a factor of four compared with the SPOT 4 satellite (10 meter resolution).
This paper presents the image quality specifications of the HRG-SPOT 5 instrument. We introduce all the efforts made on the instrument to achieve good image quality and low radiometric noise, then we compare the results with the SPOT 4 instrument’s performances to highlight the improvements achieved. Then, the in-orbit performance will be described. Finally, we will present the new goals of image quality specifications for the new Pleiades-HR satellite for earth observation (0.7 meter resolution) and the instrument concept.
During commissioning period of these satellites, thanks to their extreme agility, new calibration methods have been tested based on the observation of celestial bodies, and stars in particular. It has then been made possible to perform MTF and defocus measurement (in order to refocus), geometrical bias computation, focal plane assessment, absolute calibration, ghost images localization, micro-vibrations measurement, etc…
This article deals with the problem of satellite refocusing. By using images of stars, the problem can be considered as a phase diversity inverse problem. Significant evolution has been brought to the previous method developed during the commissioning period in order to improve accuracy and reduce operating constraints of the method.
This constant or fixed rate paradigm represents in fact a huge constraint for image compressors. Firstly, it can be hard to obtain with classical entropy coders, because their variable-length codes naturally produce variable bit-rates. Secondly and more importantly, the same compression ratio must be applied to every image, without being able to take into account its content, its degree of interest or even its entropy.
Moreover, remote sensing imagery has become a crucial instrument in a large number of civil and military applications and then, image-quality requirements are more and more difficult to satisfy because every final user has specific needs. Thus, as with fixed rate compression some image areas are better compressed than others, image-quality assessments must be established based on worst-case analysis, which provides very low compression ratios, even for state-of-the-art compressors.
CNES has been working for the last years in the characterization of image-quality requirements imposed by final users, in order to establish a relationship between the local image characteristics and the associated image quality requirements, or in other words, the tolerated compression losses.
As a result, the new functionalities included in the next generation of CNES image compressors will permit to accurately and locally adjust the compression ratio: the target quality level will be adapted for every area in the image taking into account not only its entropy but also its degree of interest.
This new trend has required the adoption of variable rate compression, which has had a significant impact in other associated elements such as mission scheduling and storage. Other interesting on-board processing techniques have also been introduced in order to fully exploit the capacities of this new kind of compression.
The CNES Pleiades-HR satellites have been launched December 17th 2011 and December 2nd 2012. They provide optical images to civilian and defense users with a resolution of 70 cm and a swath of 20 km in false or natural colors. Coverage is almost world-wide with a revisit interval of 24 h.
The new capabilities offered by these satellites agility allowed imagine new methods of image calibration and performances assessment. This paper presents all the operations that were conducted by the CNES Image Quality Team during the commissioning phases and also give the main results for every image quality performance.
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