3.4.4.2. Image conversion

Image conversion

This tool allows for the conversion of several products to reflectance. Depending on the processing level of the source product, the conversion can be 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). In case the source product is already provided as surface reflectance level, the rescaling factors are applied to convert the DN to decimal values.

The following products can be processed:

• Sentinel-2 images Level-1C;

• Sentinel-2 images Level-2A;

• Landsat 1, 2, 3 MSS, 4, 5, 7, 8, 9 images Collection 2 Level-2;

• Harmonized Landsat Sentinel-2.

Tip

Information about APIs of this tool in Remotior Sensus at this link .

3.4.4.2.1. Image conversion

Once the input is selected, available bands are listed in the metadata table.

Tool symbol and name	Description
Directory containing bands	open a directory containing product bands; names of bands must end with the corresponding number; if the metadata file is included in this directory then Metadata is automatically filled
Select metadata file	select the metadata file if not included in the Directory containing bands; for Sentinel-2, the metadata file is a .xml file whose name contains MTD_MSIL1C.
Use value as NoData	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)
Apply DOS1 atmospheric correction	if checked, the DOS1 Correction is applied to all the bands
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
Add bands in a new Band set	if checked, bands are added to a new empty Band set after the conversion

Tip

For the best spectral precision one should download Surface Reflectance products (e.g., for Sentinel-2 the Level-2A Products).

Warning

For Sentinel-2 L2A images downloaded as .zip file, all the .jp2 files must be moved inside the same directory and renamed according to the band number in the ending (e.g. from name_02_10m.jp2 to name_02.jp2).

3.4.4.2.2. Metadata

Metadata are required for the process to identify the product. If the Metadata file is not inside the input directory, one can define the file path in Select metadata file. In the Metadata, all the bands found in are listed.

The table Metadata contains the following fields.

product	spacecraft	processing_level	band_name	product_path	scale	offset	nodata	date	k1	k2	band_number	e_sun	earth_sun_distance
product name (e.g., Sentinel-2)	spacecraft name (e.g., Sentinel-2)	processing level of the product (e.g., Level-2)	name of the band	path of the band	scale of the band	offset of the band	nodata value of the band	date of acquisition of the product	k1 parameter for Landsat thermal conversion	k2 parameter for Landsat thermal conversion	band number	solar irradiance of band	Earth-Sun distance

It is possible to remove bands from the table, to exclude these bands from the conversion.

Tool symbol and name	Description
	remove highlighted bands from the table Metadata

Bands having different spatial resolution are not resampled at this stage. However, when using these bands in a classification process, all the bands are resampled on the fly to the highest spatial resolution with nearest neighbor.

Tool symbol and name	Description
Script	add this function to the Script
RUN	run this function

Tip

To reduce file size, output files are saved as data type UInt16 with scale 0.0001, which are interpreted as Float32 type by GDAL.