Comparison of ILAS‐II and ground‐based FTIR measurements of O3, HNO3, N2O, and CH4 over Kiruna, Sweden

[1] The Improved Limb Atmospheric Spectrometer-II (ILAS-II), a solar occultation instrument, was developed by the Ministry of the Environment (MOE) of Japan as a successor to ILAS. The ILAS-II was launched on board the Advanced Earth Observing Satellite-II (ADEOS-II) satellite in December 2002 and took measurements between February and October 2003. Ground-based Fourier transform infrared (FTIR) measurements were taken at Kiruna (northern Sweden, 68°N, 20°E) as part of ILAS-II validation. These ground-based observations of vertical profiles of O3, HNO3, N2O, and CH4 were compared to ILAS-II measurements processed by the version 1.4 retrieval algorithm. Nineteen coincident FTIR and ILAS-II observations were determined and analyzed. The ILAS-II profiles had considerably better vertical resolution than the ground-based profiles. The vertical resolution of the ILAS-II profiles was therefore degraded to facilitate comparison between the two sets of profiles. Average relative differences were within 10 to 15% for all four gases. The ILAS-II measurements of O3, N2O, and CH4 had a negative bias relative to the FTIR measurements. However, the bias of ILAS-II measurements relative to the FTIR measurements was positive for HNO3.