Two specific calibration modes can be distinguished:

• radiometric calibration
• spectral calibration.

OLCI Radiometric Calibration

OLCI radiometric calibration processing is a complementary processing step that does not take place in the stream of processing yielding OLCI top of atmosphere radiance data (Level-1B), as radiometric calibration acquisitions are done on a much lower time frequency.

It is however, an essential part of the overall process and since it is based on OLCI on-orbit data, is considered part of the OLCI Level-1 processing. A number of its processing steps are similar to those of Earth observation Level-1 processing.

OLCI Radiometric Calibration Processing Top Level Breakdown

Note: The abbreviations represent specific OLCI ADFs:

IC = Instrument Characterisation BRDF = Bi-directional Reflectance Distribution Function OF = Orbit File (source for time correlations but also for navigation in case NAVATT Level-0 is not available as input).

OLCI Spectral Calibration

OLCI spectral calibration processing is another complementary processing stage, also based on on-orbit data acquired at low frequency, and considered to be part of OLCI Level-1 processing. It aims to accurately determine the central wavelengths of specific rows of the detector arrays and contributes to the overall accuracy and reliability of the instrument spectral model used during radiometric calibration and Earth observation data processing.

As with radiometric calibration, a number of its processing steps share commonalities with Earth observation Level-1 processing. A significant difference however, is that it requires the availability of two Level-0 products acquired on consecutive orbits.

OLCI Spectral Calibration Processing Top Level Breakdown

Note: The abbreviations represent specific OLCI ADFs:

IC = Instrument Characterisation

SDRSR = Spectral Diffuser Relative Spectral Reflectance

OF = Orbit File (source for time correlations but also for navigation in case NAVATT Level-0 is not available as input).