The Greenhouse gases Observing SATellite (GOSAT) monitors carbon dioxide (CO2) and methane (CH4) globally from space. The Thermal and Near infrared Sensor for Carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) installed on GOSAT measures spectra absorbed by atmospheric minor components including greenhouse gases in infrared wavelength regions. This paper describes the characterization and validation of the CO2 and CH4 profiles retrieved from the thermal infrared (TIR) spectra observed by GOSAT. The retrieved CO2 and CH4 profiles were compared with the corresponding aircraft data provided by the National Oceanic and Atmospheric Administration (NOAA)/Earth System Research Laboratory (ESRL)/Global Monitoring Division (GMD)/Carbon Cycle Greenhouse Gases(CCGG) group. This group has conducted an aircraft program since 1992 to collect air samples mainly in North America. Each insitu aircraft profile was compared with those retrieved from TIR spectra without considering the effect of its averaging kernel. The root mean square (RMS) and bias errors of the retrieved CO2 and CH4 profiles were evaluated seasonally and with respect to atmospheric pressure. This comparison with aircraft data provides significant information for further improvement of the TIR retrieval algorithm.
Continuous validation of data observed by satellites, such as Greenhouse gases Observing SATellite (GOSAT), is
important to qualify the long-term trends of greenhouse gases. High-precision data over the restricted region measured
by ground-based high-resolution Fourier transform spectrometers (g-b FTS), airborne in-situ instruments, and flask
sampling devices have been used for the validation of satellite data. As part of CAL/VAL (Calibration/Validation)
activities of the GOSAT, airborne flight campaigns were performed over Tsukuba and Moshiri using the ground-based
FTS, airborne in-situ and flask devices, and 1.57-μm Laser Absorption Sensor (LAS). Airborne flask sampling and insitu
carbon dioxide (CO2) sensors were carried out to obtain vertical profiles of the CO2 mixing ratio while ground-based
FTS and LAS measured solar direct spectra and weighted column-averaged CO2, respectively. Those results were used
to decide a calibration factor of the ground-based FTS and compared with GOSAT products over Tsukuba. We will
report the comparison results of the aircraft campaign measurements and the retrieval value from the FTS.
A 1.57-μm laser remote sensor using differential absorption spectrometory is being developed as a candidate for the next
space-based mission to observe atmospheric CO2 and/or other trace gases. In a previous study, the performance of a
proto-type system with sinusoidal modulation was evaluated based on ground and airborne measurements. The airborne
measurements showed that the LAS with sinusoidal modulation could detect strong CO2 plume, and suppress the impact
of an aerosol layer over high surface reflectivity. Based on those results, an outline of LAS system on the space platform
such as the International Space Station Japan Experimental Module (ISS-JEM) was desined. However, an elevated layer
in the observation path is still remain, which leads to reduce effective observed data as long as current sinusoidal
modulation is employed. In order to prevent the impact of elevated layer, different modulation schemes such as random
or frequency modulation are capable. We are currently improving the LAS system with a chirp modulation scheme for
the purpose. Some of recent airborne measurements using sinusoidal modulation and ground-based measurements using
chirp modulation in progress will be shown in this meeting.