Wavelength calibration of spectra measured by the Global Ozone Monitoring Experiment by use of a high-resolution reference spectrum

Earthshine spectra measured by the nadir-viewing Global Ozone Monitoring Experiment (GOME) spectrometer aboard the ERS-2 satellite in the range 240 790 nm are widely in use for the retrieval of concentrations and vertical profiles of atmospheric trace gases. For the near-real time delivery of ozone columns and profiles at KNMI, a tailormade wavelength calibration method was developed. The method uses a high-resolution (0.01 nm) solar spectrum as reference spectrum and applies both a shift and a squeeze to the wavelengths in selected windows to find the optimal wavelength grid per window. This provides a calibration accuracy of 0.002 nm below and 0.001 nm above 290 nm. The new wavelength calibration method can be used on any wavelength window, for example to improve the calibration of spectra from the GOME Data Processor (GDP). A software package called GomeCal which performs this re-calibration, along with an improved polarisation and radiometric correction, has been made and is released via the WWW. The method can be used for any high-resolution (ir)radiance spectrometer, such as the satellite instruments SCIAMACHY, OMI and GOME-2.