Vicarious calibration of MERIS over dark waters in the near infrared

摘要

We propose to evaluate the calibration of MERIS (MEdium Resolution Imaging Spectrometer) over dark waters in the near infrared. We work with 5 months of data, from July to November 2003, over five world sites: Venice and Lampedusa in Italy, El Arenosillo in Spain, MOBY/Lanai and CalCOFI/San Nicolas in the United States. The sites are all equipped with a CIMEL station that forms part of the AERONET network. The basic idea is to associate CIMEL sky radiance measurements with MERIS level-1b data in a twin geometry which corresponds to the same scattering angle. This vicarious calibration relies on an accurate description of the atmospheric scattering based on the CIMEL measurements. After a selection of MERIS and CIMEL data we finally obtained 8 days for the calibration task-about 10% of the initial dataset. We achieved a match-up analysis at 6 MERIS wavelengths, from 884 nm to 664 nm, in the near infrared (NIR). Results show an agreement between the onboard calibration and our method within 1.5% in the NIR which falls in the expected accuracy of the two methods.