User Manual - pancroma

40. Working with Landsat Surface Reflectance Data________________________________________________________________As explained in other sections of this Manual, remotely sensed data is used inseveral different forms. The raw data from satellites is stored as integer DigitalNumbers (DNs) with varying formats of quantization. Typical quantizationformats are 8-bit, 11-bit and 16-bit. Although an efficient way to store data, thesenumbers do not correspond directly to any physical parameter.TOA Radiance is the total amount of electromagnetic energy that the satellitesensor intercepts, usually expressed in terms of watts per steradian per squaremeter (W·sr −1·m −2 ). TOA Reflectance is the Radiance, corrected for the solarelevation angle and distance from the sun. Such a correction allows for bettercomparison between images and to archived reflectance spectra.Surface Reflectance is TOA Reflectance corrected for atmospheric effects. It isthe fraction of incoming solar radiation that is reflected from Earth's surface.Surface reflectance approximates what would be measured by a sensor held justabove the Earth's surface, without any artifacts from the atmosphere orillumination and viewing geometry. Surface reflectance is the highest qualityremotely sensed surface parameter in the solar reflective wavelengths (i.e.,visible and infrared), providing the best possible input for virtually all higher-levelsurface geophysical parameters, for example vegetation indices, albedo, burnedarea, land cover, prospecting, and land cover change. Removing atmosphericartifacts also increases the comparability between images of Earth's surfacetaken at different times, making it the most useful parameter for studying changeeffects.Landsat surface reflectance data is archived at the GLCF and USGS GLOVIS.PANCROMA TM supports both formats. The GLCF data is presented as sixstandard multispectral band files (bands 1, 2, 3, 4, 5 and 7) plus a seventh TIRband. The data is archived in 16-bit integer format. PANCROMA TM will read the16-bit data and convert it to 8-bit unsigned integer format (i.e. 256 discretequantization levels). This is done in order to facilitate memory management andto display the data using a standard 8-bit color model. In order to use surfacereflectance data, just open the archived TIFF format files as usual. The surfacereflectances can be combined and manipulated in the same way as standardLandsat.Note that this data often contains anomalously high reflectance values. Thesecan darken the image and also cause the majority of the reflectance values tolose precision (often to two significant decimal figures.)GLOVIS archives Landsat reflectance data a six-file (Planar Configuration=2) 8-bit bundle format. PANCROMA TM will decompose this file into six individual 8-bit110