Conversions among sigma nought Ïƒ 0 , beta nought Î² 0 and gamma nought Î³ 0 generally can be accomplished with the following equations:where Î¸ i,j is the incidence angle for pixel (i, j). For most of the missions supported by SNAP, such as ALOS, ASAR, Cosmo-Skymed, ERS, Iceye, Paz, Risat-1 and TerraSAR-X, the conversions among Ïƒ 0 , Î² 0 , and Î³ 0 can be done this way. For the conversion, the incidence angles for all pixels are required, which could be from a tie point grid or a geocoded incidence angle mask (GIM).However, for some other missions such as Radarsat-2, RCM, NISAR and Sentinel-1, the calibration factors are provided as separated LUTs for Ïƒ 0 , Î² 0 , and Î³ 0 , thus the conversions among them cannot be accomplished with the equations above. In this case, retro calibration should be performed first to get the original DN value, and then new calibration is applied to the recovered DN value. All LUTs for the calibration of Ïƒ 0 , Î² 0 , and Î³ 0 are required.In either case, the source product to be converted cannot be processed product, e.g. multilooked product or speckle filtered product. This is because after processing the pixel value has been modified and it is hard to perform the retro calibration. However, the source product can be a subset of the original product. Conversion among Ïƒ 0 , Î² 0 , and Î³ 0 in this case is still possible as long as the subset definition is available.In this project, all the existing calibrators will be updated to1. Save calibration factors and other information needed for the conversions;2. Allow input product being calibrated Ïƒ 0 , Î² 0 , and Î³ 0 ;3. Be able to transform between Ïƒ 0 , Î² 0 , and Î³ 0 ;4. Be able to handle subset.

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