[A-AS09] Atmospheric Chemistry

[AAS09-04] Measurement of XCO2 using a solar tracking spectrometer (CASTLE-CO2) for the validation of satellite data

*Ryoichi Imasu¹, Yutaka Matsumi², Isamu Morino³, Yutaka Arai¹ (1.Atmosphere and Ocean Research Institute, The University of Tokyo, 2.Nagoya University, 3.National Institute for Environmental Studies)

Keywords:carbon dioxide, spectrometer, observation ship, XCO2

Mapping observation of carbon dioxide (CO₂) have been conducted over the Kanto Plain using the Greenhouse Gas Observation Satellite (GOSAT) and its successor GOSAT-2 in their targeting mode in order to estimate CO2 emissions from the Plain since 2017. For validating the satellite measurement of column-averaged dry-air mole fractions of carbon dioxide (XCO₂), ground-based measurements have been carried out using a solar tracking spectrometer, Compact Array Spectrometer Targeting Local Emissions of CO₂ (CASTLE-CO2) at observation sites in Tokyo (center of the city), Saitama (suburbs), Tsukuba (TCCON site), and Minamitorishima (background). The same equipment is also installed on the Japan Meteorological Agency's research vessel Ryofu Maru, and observation have been made near the coastal zone of Japan, in the southern seas up to the equator, and east to around 165 degrees east longitude. This equipment uses a grating spectrometer (wavelength resolution is approximately 2 cm^-1) of OptoSirius Corporation and is connected to a solar tracking system using a single-mode optical fiber. Because the spectral resolution of CASTLE-CO2 is lower than that of the spectrometer used in the TCCON (Total Carbon Column Observing Network), it is not possible to impose constraints that theoretical calculation reproduces the shape of the observed absorption line when analyzing XCO₂ from the spectrum. Therefore, we have adopted a unique analysis method to determine the spectral sensitivity characteristics of the device using theoretically calculated spectrum corresponding to the XCO₂ values obtained with the TCCON system. In the presentation, we will report on the details of the analysis method and characteristics such as daily and seasonal variations in XCO₂ measured at each site.