QDOAS Projects Properties : Undersampling page
The undersampling is a well-known problem of GOME onboard the satellite ERS-2. It arises from the poor sampling ratio of the GOME instrument (2 to 3 pixels/FWHM of the resolution of the spectrometer) which results in a lost of spectral information when interpolating earthshine spectra during the DOAS fitting process. The problem can be corrected using ad-hoc cross-sections obtained by simulating the effect from a high-resolution solar reference. Undersampling cross-sections can be pre-calculated using the QDOAS Undersampling tool or they can be calculated in real time, just after the wavelength calibration procedure using the corrected grid and the determined slit function. Further details can be found in the QDOAS software user manual. By default no undersampling correction is applied.
In Fixed phase and Automatic phase methods, undersampling cross-sections are calculated from a high resolution solar spectrum convolved on an oversampled and an undersampled grids with the instrument slit function (according to calibration options, the slit function characterized by the calibration procedure or a slit function provided by the user in the slit page of projects Properties). This field operates only in Fixed phase method.
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