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Course 2B - Sentinel-2 Surface Reflectance

Sentinel-2 Surface Reflectance Tutorial w/ Imagery (below) Using Free QGIS Software (Course 2B)

Other Surface Reflectance Guides: Sentinel-2 w/ArcGIS  Landsat 8 w/ArcGIS  Landsat 8 w/FreeQGIS

FOR A LESS DETAILED TUTORIAL use: Simplified Sentinel-2 Conversion to Surface Reflectance Steps

DOWNLOAD FREE QGIS HERE; ACCESS QGIS USER MANUAL HERE.

Use Course 1A (Downloading & Installing Free QGIS) for help installing QGIS on computer.

This easy tutorial (which is also Course 2B) applies Image-Based Atmospheric Correction to convert Sentinel-2 imagery to surface reflectance (SR), which is essentially a process of establishing then deducting atmospheric scatter reflectance from Top of Atmosphere (TOA) reflectance. This particular guide is designed to be used with Free QGIS software (can be downloaded from page on this website by accessing link below). If you have ArcGIS software, you can use the tutorial for ArcGIS software (applies to any GIS software that can produce a raster attribute table). Sentinel-2 can only be downloaded in TOA integer format, but a free toolkit is available online that can be used to convert Sentinel-2 to SR - this tutorial shows how to convert to SR independently in order to properly apply imagery. Please read: About Landsat & Sentinel-2 Surface Reflectance.

Related Page: Landsat 8 / Sentinel-2 Rare Imagery Comparison Download

Sentinel-2 Download Extent - Northwest Ohio (Eastern Corn Belt, USA; 7/19/16 (6.2 x 6.2 miles)


* IMPORTANT: You can use imagery as it is upon download (no processing necessary) to show relatively higher and lower areas of reflectance all year long. However, if converting to SR for visible bands, use imagery with a solar elevation > 45⁰ (for mid-latitudes in the northern hemisphere, this is from about the middle of March to the middle of September for Landsat and Sentinel-2 [opposite in southern hemisphere). THIS DOES NOT APPLY TO NIR AND SWIR BANDS, AS THEY REMAIN ACCURATE AT VERY LOW SOLAR ELEVATIONS. TOA reflectance for visible bands starts becoming too high as the solar elevation becomes lower than about 45⁰ (the shorter the wavelength, the more inaccurately high; so blue is the least accurate, followed by green then red). 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 SR COMPARISONS & DOWNLOADS.

 

IMAGERY BACKGROUND & TUTORIAL IMAGERY DOWNLOADS

(Tutorial starts below downloads; more band information is included at bottom of page)

Naming convention for compressed zip file downloads below (composite Image includes multiple bands) is as follows:

S2 (Sentinel-2 Satellite)_Date (MM/DD/YYYY)_Band Number_Band Central Wavelength (based on chart below)_Band Description_ Band Resolution (meters). (Red edge is the vegetation spectral range where there is a steep increase from very low red reflectance [about 5%] to relatively high NIR reflectance [about 50%] - reflectance amounts can vary according plant and range boundaries may vary depending on the source.)

Pixel values represent Top of Atmosphere (TOA) reflectance units x 10,000 (for example, 0.50 TOA units correspond to a 5000 pixel value; .025 is 250).  

Please read prior to downloading: The downloaded compressed file name for the Composite Bands file starts with the number "0", band 1-9 files start with the band number, while band 10-12 files start will "B", then the band number (this was a way to have files ordered by band number on this page). Files decompress to original Sentinel-2 file name; see the following  page for Sentinel-2 image file naming convention: https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/naming-convention. Images have level 1C processing and are .jp2 files, except for the Composite Band file which is a .tif file. The Composite Bands (band 11 [SWIR], band 8a [NIR], band 4 [red]) file was processed here with the bands that can be downloaded below.