[GIS] Carrying out atmospheric correction on Sentinel-2 data from Amazon Web Services

amazon s3atmospheric-correctionjpeg 2000sentinel-2sentinel-snap

I'm wondering what the best method is for correcting Sentinel-2 images downloaded in JP2 format (from Amazon Web Services – AWS) to BOA reflectance? As the files downloaded from the sentinel scihub in SAFE format are huge (usually about 6GB) and really cumbersome to process in the SNAP toolbox, I've been downloading the bands I need from Amazon Web Services in JP2 format, then converting them to layer-stacked GeoTIFF images in QGIS. But I need to correct them to BOA reflectance and don't know how best to do this.

Is it possible to use sen2cor in the SNAP toolbox with JP2/GeoTIFF images downloaded and processed from AWS?

Best Answer

Some BOA products now may be downloaded directly from a S3 bucket of L2A data:

http://sentinel-pds.s3-website.eu-central-1.amazonaws.com/

s3://sentinel-s2-l2a in EU Central region for L2A data over Europe, dating from 28th of March onward (the data is in a Requester Pays bucket which means that you can access it freely within the EU Central region, but you will incur charges if you download it elsewhere)

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[GIS] How is Sentinel 2 MSI Natural Colours Profile in SNAP calculated

the RGB image in snap is built using the red, green and blue bands of Sentinel-2 MSI: respectively bands 4, 3, 2 (as you can see on the snap shot, those bands are selected by default). the "Profiles" in this case are predefined colour composites to visualize the data (only 3 out of the 13 spectral bands of Sentinel-2 can be sen by the human eye at once).

You can create a similar geotif with gdal by creating a stack of those three bands, located in the /GRANULE/yourimagename/IMG_DATA directory

gdalbuildvrt -separate output.vrt image_B04.jp2 image_B03.jp2 image_B02.jp2
gdal_translate output.vrt output.tif -co TILED=YES -co COMPRESS=LZW -co BIGTIFF=YES

The advantage of using SNAP is that you do not need to unzip the file archive in order to open the image, and it is easier to select a subset and mosaic.

For color stretching, the fastest way in SNAP is to use the color manipulation. By default it uses the statistics of the image, but on my example below there was a lot of clouds, so the colour stretching had to be adjusted (except if you are interested in clouds...). Note that this is on the fly manipulation, so the pixel values are not modified. You could also do this with command lines, but is is difficult to automate on raw data that have not been atmospherically corrected and cloud screened (cloud, cloud shadow, large water area... can strongly affect the statistics).

[GIS] How to process Sentinel-2 data from AWS

Thanks to marcusN who pointend me to the ESA announcemet: https://scihub.copernicus.eu/news/News00092 There will be format change shortly, which means also, that the product will be delivered on per tile (granule) basis on ESA data hub.

Best Answer

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[GIS] How is Sentinel 2 MSI Natural Colours Profile in SNAP calculated

[GIS] How to process Sentinel-2 data from AWS

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