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Review
Atmospheric and hydrospheric sciences
202307202307
Greenhouse gases observing satellite 2 (GOSAT-2): Mission overview
Imasu R, Matsunaga T, Nakajima M, Yoshida Y, Shiomi K, Morino I, Saitoh N, Niwa Y, Someya Y, Oishi Y, Hashimoto M, Noda H, Hikosaka K, Uchino O, Maksyutov S, Takagi H, Ishida H, Nakajima TY, Nakajima T, Shi C
GOSAT-2, GOSAT, Carbon dioxide, Methane, Carbon monoxide, Black carbon, Solar-induced, chlorophyll fluorescence, TANSO-FTS-2, TANSO-CAI-2, Intelligent pointing mechanism
Artistic image of GOSAT-2 in orbit (left-top), schematic image of the TANSO-FTS-2 sensor (left-bottom). Examples of observed column-averaged dry-air mole fraction products of CO2 (right-top), CH4 (right-middle), and CO (right-bottom). Values are averaged in each 2.5° mesh area for March 2019.
The Greenhouse gases Observing SATellite 2 (GOSAT-2) was launched in October 2018 as a successor to GOSAT (launched in 2009), the first satellite to specialize in greenhouse gas observations. Compared to the GOSAT sensors, the sensors of GOSAT-2 offer higher performance in most respects. The quality and quantity of data from observations are expected to be improved accordingly. The signal-to-noise ratio (SNR) is better in both the SWIR and TIR bands of TANSO-FTS-2, which is the main sensor of GOSAT-2. This improvement ultimately enhances the accuracy of greenhouse gas concentration analysis. Furthermore, because of the improved SNR in the SWIR band, the northern limit at which data are obtainable in high-latitude regions of the Northern Hemisphere in winter, where observation data have remained unavailable because of weak signal strength, has moved to higher latitudes. As better data are obtained in greater quantities, progress in carbon cycle research for high-latitude regions is anticipated. Moreover, the improvement of SNR in the TIR band is expected to be considerable. Particularly, the resolutions of the vertical concentration distributions of CO2 and CH4 have been improved drastically. The first function introduced for GOSAT-2 that is not in GOSAT is an intelligent pointing mechanism: a cloud area avoidance function using the in-field camera of TANSO-FTS-2. This function can increase the amounts of observation data globally and can improve the accuracy of CO2 emissions estimation and measurements of uptake intensity. The effects are expected to be strong, especially for the tropics because cumulus clouds are the most common cloud type. The intelligent pointing system can avoid the clouds effectively. Another important benefit of TANSO-FTS-2 is that the wavelength range of Band 3 of SWIR has been expanded for measuring carbon monoxide (CO). Because CO originates from combustion, it is used to evaluate some effects of human activities in urban areas and biomass burning in fields. Particularly, black carbon-type aerosols can be measured by the sub-sensor, TANSO-CAI-2, to assess biomass burning along with CO2 and CO by TANSO-FTS-2.
