IN-FLIGHT CALIBRATION FOR GOSAT TANSO

摘要

The Japanese greenhouse gas observing satellite “IBUKI” (GOSAT) is conducting a mission to observe the greenhouse gases, carbon dioxide (CO_2) and methane (CH_4), from space using a Fourier transform spectrometer and a pushbroom imager. GOSAT carries the thermal and near-infrared sensor for carbon observation (TANSO) package, which is composed of a main TANSO-FTS (Fourier transform spectrometer) sensor and a TANSO-CAI (cloud and aerosol imager) sub-sensor. TANSO-FTS uses four spectral bands-shortwave infrared (SWIR) to thermal infrared (TIR) regions-for observing greenhouse gases. Bands 1–3 are SWIR channels and Band 4 is a TIR channel. TANSO-CAI retrieves information on clouds and aerosols; this information is used for improving the accuracy of greenhouse gas retrieval. GOSAT was launched with the H-IIA Launch Vehicle No. 15 (H-IIA F15) at 03:54:00 Universal Time (UT) on January 23, 2009 from the Tanegashima Space Center. The launch vehicle flew smoothly, and at about 16 min after liftoff, the separation of the IBUKI was confirmed. At 08:15 UT on January 24, 2009, the next day of the mission, IBUKI completed critical phase operations and transitioned to the approximately three-month-long initial functional check phase to check onboard equipment functioning. After initial functional checking was completed in early April, initial calibration was conducted over the following three months. Over the last three years, GOSAT has operated normally in acquiring observational data. GOSAT’s sensors were characterized in pre-flight testing (PFT), and a Level 1 algorithm was developed based on the evaluation of the PFT data. After launch, observational data was evaluated in the initial calibration and validation phase, using onboard and vicarious calibration methods. The results of the evaluation of calibration data are reflected regularly to improve the algorithm for providing calibrated Level 1 products. Starting in October 2009, Level 1 products have been released to the public, and Level 2 products have been released since February 2010. FTS SWIR Level 3 data products-global distributions of XCO_2 and XCH_4-have been available for public download through the GOSAT user interface gateway since November 30, 2010. FTS SWIR Level 3 data products are derived from FTS SWIR Level 2 data products, and include estimated results for areas from where no observational data are available.