Intercomparison and validation of ILAS‐II version 1.4 target parameters with MIPAS‐B measurements

Abstract

A flight of the balloon‐borne version of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS‐B) was performed from Kiruna (Sweden, 68°N, 21°E) on 20/21 March 2003 as part of the validation program of the chemistry instruments MIPAS, GOMOS, and SCIAMACHY aboard the European environmental satellite ENVISAT. The 15 hour long duration of this flight provided a good match with the Japanese Improved Limb Atmospheric Spectrometer (ILAS)‐II sensor aboard the ADEOS‐II satellite, launched in December 2002, in addition to the primary goal of ENVISAT validation. The MIPAS‐B flight data coincided nicely with one of the early operational periods of the ILAS‐II instrument, offering one of the sparse opportunities to validate the whole set of trace species measured by ILAS‐II during its unfortunately short lifetime. Radiance spectra were observed by MIPAS‐B at nearly the same location that was observed by ILAS‐II about 5.5 hours prior to the sampling of MIPAS‐B. The intercomparison of ILAS‐II atmospheric target parameters (version 1.4) to profiles measured by MIPAS‐B has shown that for the species O3, N2O, CH4 (below about 22 km), HNO3, ClONO2, and CFC‐11 (CCl3F), a predominantly good consistency with MIPAS‐B has been achieved within the combined errors. However, atmospheric parameters like temperature, H2O, NO2, and N2O5 are widely characterized by low biases compared to MIPAS‐B results while CFC‐12 (CCl2F2) exhibits a high bias in comparison to the balloon‐borne observations. Therefore ILAS‐II profile retrievals of temperature, H2O, NO2, N2O5, and CFC‐12 cannot be assumed to be validated at the present time.