Spectral Calibration Mode
The spectral calibration mode product consists of absolute central wavelengths of selected CCD rows that shall be used to update the corresponding OLCI spectral characterisation Auxiliary Data File (ADF) used in Earth observation mode.
This product, OL_1_SPC, which is not available to the user, includes one measurement file and two annotation files, described below. The metadata information is gathered in a SENTINEL-SAFE product manifest.
The measurement file, cal_wavelengths.nc.nc, includes spectral calibration wavelength data and is described in the following table. Only the main variables and their dimensions are reported, not their associated attributes.
| Element name | Description | Dimensions |
| Specific Dimensions | ||
| detectors | Number of instrument detectors per frame (covering the five cameras). | |
| bands | Number of OLCI bands, excluding the smear band. | |
| bands_total | Number of OLCI bands, including the smear band. | |
| dark_pixels | Number of dark pixels for the five OLCI cameras. | |
| blank_pixels | Number of blank pixels for the five OLCI cameras. | |
| diffuser_acquisitions | Number of frames acquired during the second orbit of the spectral calibration sequence while CM is in spectral diffuser position. | |
| selected_rows | Number of rows selected to compute the absolute central wavelength. | |
| orbit | Number of orbits treated during the run (corresponds to orbits n and n+1). | |
| Included Variables | ||
| absolute_central_wavelength | Absolute Central Wavelengths for all pixels of all cameras and the N_Bands_Sets selected rows. | selected_rows diffuser_acquisitions detectors |
| shutter_mean_dark_pixels_time | Time average of the dark pixels of the five cameras at the configured bands for spectral calibration plus the smear band, all acquired in shutter position of both orbit N and N+1. | bands dark_pixels orbit |
| shutter_mean_blank_pixels_time | Time average of the blank pixels of the five cameras at the configured bands for spectral calibration plus the smear band, all acquired in shutter position of both orbit N and N+1. | bands blank_pixels orbit |
| diffuser_mean_dark_pixels_time | Time average of the dark pixels of the five cameras at the configured bands for spectral calibration plus the smear band, all acquired in diffuser position of both orbit N and N+1. | bands dark_pixels orbit |
| diffuser_mean_blank_pixels_time | Time average of the blank pixels of the five cameras at the configured bands for the spectral calibration plus the smear band, all acquired in diffuser position of both orbit N and N+1. | bands blank_pixels orbit |
The two annotation files are:
- time_coordinates.nc, providing the measurement time stamp for each frame acquired during the second orbit of the spectral calibration sequence while the Calibration Mechanism (CM) is in the spectral diffuser position
- a general annotation file, SC_annotation.nc, providing the selected rows index providing wavelengths, associated quality flags and CCD temperature in shutter and diffuser mode. The quality flag indicates if the wavelength is considered invalid (and the reason why) and if the linear model of reflectance, derived from a least square fitting between the measured reflectance and the reference one, is not accurate enough.