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Crop Agriculture

Sentinel-2 Surface Reflectance Tutorial

(Sentinel-2 Bands 1 - 12 Can Be Downloaded Below)

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

For a less detailed tutorial use Simplified Landsat 8 & Sentinel-2 Conversion to Surface Reflectance Steps

This easy tutorial applies Image-Based Atmospheric Correction to convert Sentinel-2 imagery to surface reflectance (SR), which is essentially a process of establishing and deducting atmospheric scatter reflectance from Top of Atmosphere reflectance. This particular guide is designed to be used with ArcGIS, but can be applied to any GIS software that can produce a raster attribute table. If you do not have the appropriate software, you can use the tutorial for Free QGIS Software. 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.

(Tutorial & Imagery Downloads are Below)

Related Page: Landsat 8 / Sentinel-2 Rare Comparison & Data

Sentinel-2 is comprised of two satellites (2A & 2B) that produce free ongoing imagery with a combined revisit time of 5 days at the equator and 2 to 3 days at the mid-latitudes. Sentinel-2 has finer pixel resolution and more bands that Landsat (however, Landsat remains excellent data and the two can and should be used together). In order to convert to SR, apply the steps in the Tutorial below. Sentinel-2 Level 1C imagery can be downloaded from the Copernicus website by accessing the Recommended Free Imagery Sources on the top menu. 

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

Sentinel-2 Atmospheric Correction/Surface Reflectance Tutorial & Imagery Download Extent

* IMPORTANT: If converting to SR for visible bands, try to 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). NIR and SWIR can be converted to SR at any solar elevation.Retrieved Sentinel-2 SR with the relative scatter with the methods described on this website have 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 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 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.