[A-AS01] Global Carbon Cycle Observation and Analysis

[AAS01-P07] Characteristics of Version 1.0 CO₂ data retrieved from TIR band of GOSAT/TANSO-FTS

*Naoko Saitoh¹, Shuhei Kimoto¹, Ryo Sugimura¹, Ryoichi Imasu², Kei Shiomi³, Akihiko Kuze³, Toshinobu Machida⁴, Yousuke Sawa⁵, Hidekazu Matsueda⁵ (1.Center for Environmental Remote Sensing, Chiba University, 2.Atmosphere and Ocean Research Institute, University of Tokyo, 3.Japan Aerospace Exploration Agency, 4.National Institute for Environmental Studies, 5.Meteorological Research Institute)

Keywords:satellite remote sensing, retrieval algorithm, validation analysis, CO2

Greenhouse Gases Observing Satellite (GOSAT) was launched on 23 January 2009, and has continued to make global observations of greenhouse gases, including both nadir and off-nadir measurements, for more than seven years since its launch. Carbon dioxide (CO₂) concentrations in several atmospheric layers can be retrieved from radiance spectra of the thermal infrared (TIR) band of Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on board the GOSAT. We have analyzed the latest released version of the TIR Level 2 (L2) CO₂ product (Version 1.0). We compared TANSO-FTS TIR V1.0 CO₂ data and CO₂ data obtained in the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project. The comparisons over several airports showed that the TIR V1.0 CO₂ data had a 1-2% negative bias in the middle troposphere; the magnitude of the bias varied seasonally and regionally. The comparisons in the upper troposphere and lower stratosphere (UTLS), where the TIR band of TANSO-FTS is most sensitive to CO₂ concentrations, showed that the averages of the TIR upper atmospheric CO₂ data agreed well with the averages of the data obtained by the CONTRAIL Continuous CO₂ Measuring Experiment (CME) within 0.1% and 0.5% for all of the seasons in the Southern and Northern Hemisphere, respectively. The magnitude of bias in the TIR upper atmospheric CO₂ data did not have a clear longitudinal dependence. The comparison results for flights in northern low and middle latitudes showed that the agreement between TIR and CONTRAIL CO₂ data in the upper troposphere was worse in the spring and summer than in the fall and winter. The negative bias in northern middle latitudes made the maximum of TIR CO₂ concentrations lower than that of CONTRAIL CO₂ concentrations, which leads to underestimate the amplitude of CO₂ seasonal variation. CO₂ growth rate estimated from the TIR UTLS CO₂ data from 2010 to 2012 was slightly lower (-0.6 ppm) than that from the CONTRAIL level flight data during the same period, which increases the differences between TIR and CONTRAIL CO₂ concentrations in UTLS.