Passive and Active Remote Sensing of Greenhouse Gases in the GOSAT Project
Abstract:The Greenhouse gases Observing SATellite (GOSAT), launched on 23 Jan. 2009, is the world's first satellite dedicated to measuring concentrations of the two major greenhouse gases, carbon dioxide (CO2) and methane (CH4), from space. Column-averaged dry air mole fractions of CO2 and CH4 (XCO2 and XCH4) are retrieved from the Short-Wavelength InfraRed (SWIR) spectral data observed with the Thermal And Near-infrared Sensor for carbon Observation - Fourier Transform Spectrometer (TANSO-FTS) onboard GOSAT. The present NIES full physics SWIR retrieval algorithm (ver. 02.xx) showed smaller biases and standard deviations (-1.48 ppm and 2.09 ppm for XCO2 and -5.9 ppb and 12.6 ppb for XCH4, respectively) than those of the ver. 01.xx by comparing with data of the Total Carbon Column Observing Network (TCCON). GOSAT retrievals from the GOSAT TANSO-FTS SWIR spectra for more than five years are now ready for scientific research, but may be still influenced by thin aerosols and clouds.
Under GOSAT validation activities, we made aircraft observation campaigns to validate the GOSAT products and calibrate TCCON FTSs installed in Japan. In their campaigns, we also made partial column measurements of CO2 with an airborne laser absorption spectrometer, and comparison of ground-based CO2Differential Absorption Lidars with aircraft measurement data. Their active remote sensing experiments are for development of new validation methodology for passive space-based mission and fundamental development for future active space-based mission.
The Ministry of the Environment, the Japan Aerospace Exploration Agency, and the National Institute for Environmental Studies also started the development of the follow-on satellite, GOSAT-2 in 2013. GOSAT-2 will be launched in 2017 – 2018. Instruments onboard GOSAT-2 are similar to current GOSAT.
The SWIR passive remote sensing of greenhouse gases would be more or less affected by aerosols and thin cirrus clouds. Therefore, active remote sensing is expected to solve it and extend observations during nighttime and to be complementary with passive remote sensing which is adequate to wider observations.
In this presentation, we will show results on GOSAT observations, validation activities, and lessons learnt from passive remote sensing of greenhouse gases for next-generation remote sensing.