18.104.22.168 Saturated Pixels
MERIS samples may be affected by phenomena outside the range of the useful measurements; i.e., a spectral radiance between 0 and Lsat. Such samples are totally invalid, the corresponding cells being affected temporarily or permanently. When possible, invalid pixels should be replaced by a good estimate.
Such phenomena are:
1. Saturation by radiance level above Lsat (caused by, e.g., Sun glint, cloud, bright land or snow /ice), which affects cells temporarily (typically several columns in several bands over several frames).
2. Recovery from saturation. After saturation, components of the acquisition chain need some time (a few pixel columns) to recover; in the meantime the measurement is affected.
3. Blooming. Samples in bands and columns close to a saturated one may be temporarily affected by photon or photoelectrons diffusing from the saturated pixel.
4. Glitches, high-intensity impacts (e.g., laser) generate isolated high value samples.
5. Dead pixel. Due to manufacturing defects or to ageing in space, the response of some CCD cells to light may "die;»I.e., permanently deviate too much (to the extent that gain correction is not usable) from the useful measurement range. Such dead pixels need to be known.
Samples affected by saturation/recovery/blooming (1, 2, 3) are flagged.
Samples corresponding to dead pixels (5) are replaced with a cosmetically interpolated value after radiometric calibration within the radiometric processing step.
Glitches are neither detected nor corrected due to unavailability of a simple model for detection.