Calibration method to correct for cloud-induced wavelength shifts in Aura's Ozone Monitoring Instrument

The in-flight wavelength calibration for the Ozone Monitoring Instrument is discussed. The observed variability in the wavelength scale is two orders of magnitude larger than caused by temperature changes in the instrument. These wavelength variations are the result of rapid changes in time in the radiance levels during an individual observation as observed in the presence of clouds or snow and ice. We have developed a method to account and correct for these changes in the data processing. In February 2005 this correction was implemented in the official data processing stream. It is explained in detail how and how accurately this method works. Before correction, the error in the wavelength scale can be up to a few tenths of a pixel, after correction it is mostly less than 1/100th of a pixel, which is the pre-flight required accuracy. This means that higher level products such as e.g. the total column amounts of ozone, NO2 and SO2 are not significantly affected. It is expected that the observed wavelength variations should be observed in other hyperspectral Earth observation spectrometers besides OMI and that the correction mechanism should apply equally well.