3.4.3.6. Sentinel-2

_images/sentinel2_tab.jpg

sentinel2_tool Sentinel-2

This tab allows for the conversion of Sentinel-2 images Level-1C to the physical measure of Top Of Atmosphere reflectance (TOA), or the application of a simple atmospheric correction using the DOS1 method (Dark Object Subtraction 1), which is an image-based technique (for more information about conversion to TOA and DOS1 correction, see Image conversion to reflectance). This tool can also convert Sentinel-2 images Level-2A from DN to reflectance values.

Once the input is selected, available bands are listed in the metadata table. Bands with 20m spatial resolution are resampled to 10m resolution without changing the original pixel value (i.e. one 20m pixel is divided in four 10m pixels with the same value). To reduce file size, output files are saved as data type UInt16 with scale 0.0001, which are interpreted as Float32 type by GDAL.

WARNING: For the best spectral precision you should download the Sentinel-2 Level-2A Products (Surface Reflectance) or use the official SNAP tool for atmospheric correction (see http://step.esa.int).

3.4.3.6.1. Sentinel-2 conversion

  • Directory containing Sentinel-2 bands open_dir: open a directory containing Sentinel-2 bands; names of Sentinel-2 bands must end with the corresponding number; if the metadata file is included in this directory then Metadata are automatically filled;

  • Select metadata file open_file optional: select the metadata file which is a .xml file whose name contains MTD_MSIL1C); this is optional and can be generally ignored;

  • checkbox Apply DOS1 atmospheric correction: if checked, the DOS1 Correction is applied to all the bands;

  • checkbox Use value as NoData input_number: if checked, pixels having NoData value are not counted during conversion and the DOS1 calculation of DNmin; it is useful when image has a black border (usually pixel value = 0);

  • checkbox Preprocess bands 1, 9, 10: if checked, preprocess also bands 1, 9, 10 (i.e. 60m bands);

  • checkbox Create Band set and use Band set tools: if checked, bands are added to the active Band set after the conversion; also, the Band set is processed according to the tools checked in the Band set;

  • checkbox Add bands in a new Band set: if checked, bands are added to a new empty Band set after the conversion;

    TIP: in order to convert L2A images you should move all the .jp2 files inside the same directory and rename the files with the band number in the ending of the name (e.g. from name_02_10m.jp2 to name_02.jp2).

3.4.3.6.2. Metadata

All the bands found in the Directory containing Sentinel-2 bands are listed in the table Metadata. If the Sentinel-2 metadata file (a .xml file whose name contains MTD_MSIL1C) is provided, then Metadata are automatically filled. For information about Metadata fields read this informative page .

  • Satellite input_text: satellite name (e.g. Sentinel-2A);
  • remove: remove highlighted bands from the table Metadata;
  • input_table Metadata: table containing the following fields;
    • Band: band name;
    • Quantification value: value for conversion to TOA reflectance;
    • Solar irradiance: solar irradiance of band;
  • BATCH batch_tool: add this function to the Batch;
  • RUN run: select an output directory and start the conversion process; only bands listed in the table Metadata are converted; converted bands are saved in the output directory with the prefix RT_ and automatically loaded in QGIS;