Radiometric calibration with SNAP

Prerequisites

• Sentinel-2 SEN2COR280 Processor plugin is already installed in SNAP (see Installation of SNAP)
• If your region of interest (ROI) is located in mountainous terrain a topographic illumination correction is recommended which requires a digital terrain model. The automated download link in SNAP has recently changed. Therefore, please manually download SRTM tiles covering the ROI from this CGIAR homepage. Unzip the GeoTIFF files in a folder.
• Download a Sentinel-2 Level 1C tile from ESA's Copernicus Open Access Hub web service as a compressed zip file: Downloading Sentinel-2 images.

Start atmospheric correction

• Start SNAP Desktop.
• File --> Open Product.... Browse to the zip archive or drag and drop the file from the Windows file explorer into the SNAP tab Product Explorer.
• Optical --> Thematic Land Processing --> Sen2Cor Processor --> Sen2Cor 280
• Specify the Processing Parameters as shown in the screenshot below. Details can befound in the Sen2cor manual.

Check Display execution report on. A first run will be made with 60m pixel resolution. Computation time dependes mainly on the number of available CPUs on your local machine. Increase the NB threads accordingly to speed up parallel processing. Topographic normalization is activated with DEM correction: TRUE. For DEM directory specify the folder where dem files were downloaded and unzipped.

• Compare Output Product with Original Product. Mark the Original Product Name in Product Explorer Right Click Open RGB Image Window --> Sentinel-2 MSI Natural Colors. OK. Repeat for the Output Product.
• Window --> Tile horizontally
• Check View --> Synchronize Image Cursors and View --> Synchronize Image Views. Zoom and Pan.
• Activate a map view by clicking into the canvas of the Original Product. Click Mask Manager tab on the right.
• Check the mask layers opaque_clouds and cirrus_clouds in the Mask Manager.

• Click into the map canvas of the Ouput Product. Click Mask Manager tab on the right.
• Check the mask layers scl_cloud_shadow, scl_cloud_medium_proba, scl_cloud_high_proba, scl_thin_cirrus in the Mask Manager.

• For second run choose in Processing Parameters: Spatial Resolution: 10 (m). Be patient, processing takes some time ...