Optical Payloads onboard Japanese Greenhouse Gases Observing Satellite

The Greenhouse gases Observing SATellite (GOSAT) was launched on 23 January 23, 2009, and within a few weeks began making space-based observations, with two instruments, of carbon dioxide (CO2) and methane (CH4) concentrations in the global column. The Thermal and Near Infrared Sensor for Carbon Observation–Fourier Transform Spectrometer (TANSO–FTS) detects gas absorption spectra of both the solar short-wave infrared (SWIR) radiation reflected from the earth's surface and the thermal infrared (TIR) radiation reflected from the ground and atmosphere. TANSO–FTS is capable of detecting three narrow bands (0.76, 1.6, and 2.0 μm) and a wide band (5.5–14.3 μm) with 0.2 cm−1 spectral interval. The TANSO Cloud and Aerosol Imager (TANSO–CAI) is an ultraviolet (UV), visible, near infrared, and SWIR radiometer designed to detect cloud and aerosol interference and to provide the data for their correction. GOSAT is placed in a sun-synchronous orbit at 666 km above Earth's surface, and collects data at 13:00 local time at an inclination angle of 98°. An operation period spanning more than five years has resulted in an immense volume of useful scientific data that have been used to produce and publish many interesting articles on the topics of carbon source/sink evaluation. Research results have been very useful to improve our understanding of the global carbon cycle. Because of TANSO–FTS operation, we have learned how to improve the accuracy of XCO2 and XCH4 based on radiometric, geometric, and spectroscopic data. The current retrieval accuracy of XCO2 by GOSAT spectra of around ±2 ppm is determined by comparison with ground- and aircraft- measured data, and is much more accurate than the pre-launch ±4 ppm target of the GOSAT mission. Further improvement of the XCO2 and XCH4 retrieval algorithm for accuracy and processing speed is important for the continuing program. Here, a brief overview is provided with science and technical highlights of the GOSAT project, scientific requirements, instrument designs, hardware performance, on-orbit operation, and data processing.