[A-AS21] Atmospheric Chemistry

[AAS21-P23] Validation of GOSAT/TANSO-FTS TIR CO2 profiles using aircraft CO2 data

*Shuhei KIMOTO¹, Naoko SAITOH¹, Ryoichi IMASU², Shuji KAWAKAMI³, Kei SHIOMI³, Toshinobu MACHIDA⁴, Yousuke SAWA⁵, Hidekazu MATSUEDA⁵, Taku UMEZAWA⁴ (1.Center for Environmental Remote Sensing, Chiba University, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Japan Aerospace Expolation Agency, 4.National Institute for Environmental Studies, 5.Meteorological Research Institute)

Keywords:GOSAT, validation, CO2, aircraft measurement

Greenhouse gases Observing SATellite (GOSAT) was launched on 23 January 2009 to observe major greenhouse gases such as CO₂ and CH4. Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on board the GOSAT can observe CO₂ profiles in the thermal infrared (TIR) region, but the quality of the retrieved CO₂ profile data has not yet been fully validated. In this study, we compared GOSAT/TANSO-FTS TIR CO₂ profiles with aircraft CO₂ data to evaluate their quality. The aircraft data we used were obtained by Comprehensive Observation Network for Trace gases by Airline (CONTRAIL) project and Civil Aircraft for the Regular investigation of the atmosphere Based on an Instrument Container (CARIBIC) project, both of which are commercial airliner projects.

First, we assumed CONTRAIL data obtained during ascending and descending flights over airports as a "CO₂ profile", and then compared TIR CO₂ profiles with the CONTRAIL CO₂ profiles to which the TIR averaging kernel functions were applied. We adopted a distance between the GOSAT observation and the airport within 300 km and a time difference between the two observations within 72 hour as criteria for the comparison. Here, we used the CONTRAIL profile data obtained over the ten airports: Moscow, Amsterdam, Vancouver, Narita, Delhi, Honolulu, Bangkok, Singapore, and Djakarta. We also used CONTRAIL and CARIBIC level flight data to validate the global distributions of TIR upper tropospheric CO₂ data. We divided the level flight aircraft data into several regions, and then compared the averaged aircraft data with the averaged TIR data in each region.

From the CO₂ profile comparisons at each airport, we found the TIR data had a low bias of 1-1.5%. The magnitude of the bias varied depending on seasons and latitudes; in spring and summer in low latitude, the magnitude of the bias was larger than that in autumn and winter in mid and high latitudes. From the upper tropospheric CO₂ comparisons, the TIR data showed better agreements to the aircraft data than the a priori data, and the distribution of the TIR upper tropospheric CO₂ data had a similar pattern to the distribution of the aircraft data. In the poster, we will also report the details of the comparisons using other aircraft data.

Acknowledgements
We thank the staff and engineers of Japan Airlines, the JAL Foundation, and JAMCO Tokyo for supporting the CONTRAIL project. CARIBIC data used in this study were provided by the CARIBIC project. We also thank Dr. C. Brenninkmeijer and other members of the CARIBIC project.