The Greenhouse Gas Observing Satellite (GOSAT) observes infrared light reflected and emitted from the earth's surface and the atmosphere. Column abundances of CO2 and CH4 are calculated from the observational data. The column abundance of a gas species is expressed as the number of the gas molecules in a column above a unit surface area. GOSAT is a Japanese satellite that flies at an altitude
of approximately 666 km and completes one revolution in about 100 minutes. The satellite returns to the same point in space in three days. The observation instrument onboard the satellite is the Thermal And Near-infrared Sensor for carbon Observation (TANSO). TANSO is composed of two subunits: the Fourier Transform Spectrometer (FTS) and the Cloud and Aerosol Imager (CAI).