Normalisation of Surface Reflectance for Sentinel-2

There are other implementations which are doing a surface reflectance normalisation using the c-factor method, but I found (SEN2NBAR, SentinelHub) those don't use the detector footprints. But these detector footprints need to be used per reflectance band to calculate the view azimuth and zenith angles per pixel correctly. You can read more about it in my other article where I provide more details.

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  Surface Reflectance RGB

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  Normalised Surface Reflectance

Left: Surface Reflectance RGB

Right: Normalised Surface Reflectance RGB

The EOMasters Toolbox Pro for ESA SNAP now provides a surface reflectance normalisation using the c-factor (Roy et al.) method and is considering the detector footprints.

What is a surface reflectance normalisation good for?

Ensuring reliable comparisons of images over time and under different conditions is crucial in remote sensing. To achieve this reliability, it is essential to simulate a nadir viewing perspective. This adjustment addresses the anisotropic properties of surface reflectance and the variations in sun and observation angles.

The c-factor method, a straightforward yet effective technique, adjusts the measured surface reflectance using the MODIS BRDF model to produce Nadir BRDF Adjusted Reflectance (NBAR).

The result of this normalisation is shown in this short video.

https://video.wixstatic.com/video/6281da_50a6ae2b129749b59dcfbe864ce8e418/720p/mp4/file.mp4

This implementation supports the standard Sentinel-2 L2A data provided by ESA/Copernicus. Theoretically this can also support L2A data from Theia in the Muscate format. Unfortunately, this data does not provide correct detector footprints for the surface reflectance bands. This issue has already been reported.

More general information about this release can be found in the other blog:

Release of EOMasters Toolbox Pro v1.2

The EOMasters Toolbox Pro is available in the EOMasters Shop. You can activate a trial version when installing the plugin in SNAP. Simply request the trial key and decide after the trial period if you want to purchase it.

Tschüss & Goodbye

Marco