Impact of Improved Corrections for MIPAS Detector Non-Linearity

Abstract

Three of the five MIPAS/Envisat spectral bands are measured by detectors with a non-linear photon flux response. This non-linearity has to be corrected in the interferogram before the transformation to the spectrum is performed. Operational L1b data up to version IPF5 is processed with one fixed set of non-linearity corrections, which have been deduced from an instrument characterisation before mission start. However, the detectors are affected by ageing, i.e. the corrections can be expected to change in time. In the frame of the MIPAS QWG a new set of time dependent non-linearity corrections were deduced from in-flight measurements, and will be used in future versions of the L1b processor. Two test sets of data of eleven orbits each have been processed to L1b using the operational NL-corrections for the first and the new time dependent NL-corrections for the second data set. The impact of the time dependent NL-corrections on L2 data products is discussed. It depends on retrieval target and altitude. For Ozone differences of the new and the operational data are roughly consistent with drifts found in MIPAS O3 data compared to other instruments.