Institute of Meteorology and Climate Research

MIPAS methane succesfully validated


Bias estimation of MIPAS methane retrievals with respect to satellite reference instruments. The quantity shown is the mean estimate over all latitudes of (MIPAS-REFERENCE)/REFERENCE x 100 %. This validation study includes bias determination, assessment of stability, precision validation, analysis of histograms and comparison of climatologies. The reference instruments include the satellite instruments ACE-FTS, HALOE, SOFIE and SCIAMACHY; as well as MkIV balloon-borne solar occultation measurements and cryogenic whole-air sampling measurements.

Above 50 km altitude, MIPAS methane mixing ratios agree within 3% with ACE-FTS and SOFIE. Between 30 and 40 km an agreement within 3% with SCIAMACHY has been found. In the middle stratosphere, there is no clear indication of a MIPAS bias since comparisons with various instruments contradict each other. In the lower stratosphere (below 25 km) MIPAS CH4 is biased high with respect to satellite instruments, and the most likely estimate of this bias is 14 %. However, in the comparison with CH4 data obtained from cryogenic whole-air sampler (cryosampler) measurements, there is no evidence of a high bias in MIPAS between 20 and 25 km altitude. Precision validation is performed on collocated MIPAS–MIPAS pairs and suggests a slight underestimation of its uncertainties by a factor of 1.2. No significant evidence of an instrumental drift has been found.

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