MERIS O2 CALIBRATION USING SCIAMACHY MEASUREMENTS

摘要

A new MERIS spectral calibration method is proposed exploiting the synergy between MERIS and SCIAMACHYrnENVISAT instruments. Detailed method description and preliminary results are presented in this paper. In the O2rncalibration mode MERIS is measuring atmospheric radiances in the 750-780 nm spectral range in order to verify therninstrument ability to reproduce position and shape of O2 band-A absorption features. The same spectral range isrncovered by SCIAMACHY, although at different space and spectral resolution. When operated in this mode the MERISrnslit functions are characterized by a FWHM of 1.2 nm, while for SCIAMACHY the spectral resolution is 0.3 nm.rnGround pixel size for MERIS and SCIAMACHY are respectively 1.1x1.3 and 30x40 km2.rnThe proposed method is based on the assumption that the two instruments are probing the same atmosphere and, hence,rndetected spectral features are approximately the same. Moreover, it assumes SCIAMACHY spectral calibration to bernstable and very accurate. Nevertheless, this method can be used adopting other independent sources of oxygen data asrnreference for the inter comparison with MERIS spectra (e.g. GOME spectral measurements, HITRAN spectralrndatabase). The estimated shift refers to the entire wavelength range and not a single MERIS band. Preliminary resultsrnindicate that this simple method can efficiently detect MERIS wavelength shifts with respect to SCIAMACHY (or tornany other reference spectral database) with an accuracy of 0.01 nm along the orbit, allowing for global analysis.