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Low Solar Elevation Imagery Background (Download Included Below): Retrieved Sentinel-2 SR with the relative scatter methods described here has only been tested here for accuracy for solar elevations greater than 50⁰ and less than 30⁰; we have found that visible band, particularly the blue band, SR values become too high at solar elevations less than 30⁰ (because TOA reflectance becomes disproportionatly higher for shorter wavelengths at low solar elevations). We have not completed research for solar elevations from 30 to 50⁰. It is very likely that visible band retrieved SR, particularly the blue band, becomes increasingly less accurate (too high) as solar elevations decrease from about 45⁰ - NIR AND SWIR BANDS REMAIN ACCURATE AT VERY LOW SOLAR ELEVATIONS. Chavez (1996) stated further research for the COST model is needed for solar elevations less than 35⁰ (solar zenith angles greater than 55⁰). CLICK HERE FOR LOW SOLAR ELEVATION IMAGERY INCLUDING A LANDSAT & SENTINEL-2 SR COMPARISONS & DOWNLOADS.

12/1/16: Sentinel-2, Grant County, Washington State, USA. Downloads include: 1) Surface reflectance (SR) for Bands 2 (blue), 3 (green), 4 (red), 8a (NIR), 11 (SWIR1), and 12 (SWIR). Imagery is converted to SR with the Frequency 50 minus .008 method, where band 4 (red) is the starting scatter and relative scatter with the calculator is used to establish scatter for other bands (B4RS is band 4 relative scatter, method is explained in the Tutorial); 2) Background imagery is corresponding Sentinel-2 SWIR/NIR/Red RGB (vegetation is green). Vegetation visible band SR is somewhat high; but green surface reflectance is consistently higher than blue (and red).

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