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Chelys srl news

Over the last few months, Chelys has produced new mosaics using new and improved techniques such as SAR-sharpening, Orthorectification and Clouds and Shadows detection and removal.

The first mosaic is a MERIS reduced resolution mosaic of the world generated from over 2000 images collected between January and August 2008. The original products from the Envisat satellite were processed by the Chelys Satellite Rapid Response System (SRRS) and then projected by Chelys MOSRI. The strength of the Clouds and Shadows detection algorithm is its speed and capability for retrieving even the smallest area of valid pixel information from any cloud covered image.

The detailed view of Italy in the second mosaic, also generated by MOSRI, was created using the Chelys SAR-Sharpening technique. This technique is similar to PAN-Sharpening in that it merges a high resolution image with lower resolution multispectral imagery; however, the high resolution image used by our SAR-Sharpening method is radar image instead of a panchromatic one. In this mosaic, the level of detail in the MERIS image (250m resolution) has been greatly enhanced by merging an ASAR mosaic with a resolution of 75m. The mosaic comprises ASAR images acquired from January to July 2009, and MERIS images captured between April and November 2008.
This image is an ASAR image mode medium resolution mosaic of Italy. The source images, acquired from January to July 2009, were generated from Envisat data using SRRS, then projected, orthorectified, merged through MOSRI. The Chelys orthorectification process corrects the geometric distortion created by SAR (Synthetic Aperture Radar) instruments, whose side-looking imaging mode has an angle much greater than that of the optical image, using a DEM (Digital Elevation Model) to make the slant to ground range conversion truer to the region’s actual topography. The process selects the proper DEM according to image resolution (3 arcseconds for this image), and performs in real-time, with the entire correction process taking less than 20 seconds per product. As a finishing touch, the banding effect common to the merging of various original radar images was also automatically eliminated by MOSRI.

Envisat’s Medium Resolution Imaging Spectrometer (MERIS) acquires multi-spectral imagery of the Earth, and is used to monitor the state and evolution of the terrestrial vegetation cover. In particular, the MERIS Global Vegetation Index (MGVI), which corresponds to the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), is generated operationally as a standard level-2 product, using the radiation measured by MERIS over land surfaces. This bio-geophysical product plays a critical role in the plant photosynthetic process and is regularly used in diagnostic and predictive models to compute the primary productivity of the vegetation canopies. FAPAR has been established as a fundamental surface parameter by international organizations including the Global Climate Observing System (GCOS), charged with providing data on the Earth’s climate system.

Chelys has developed a new processor that is able to process and directly extract the FAPAR index from level 0 reduced or full resolution (but also from level 1), generating the relative false-colored image just a few seconds after the original data is ingested.

In the next few weeks, a processor that will systematically generate these vegetation index images will be incorporated in the SRRS (Satellite Rapid Response System). As soon as enough images have been collected, it will be possible to generate mosaics as well.

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