GOSAT: infer greenhouse gases from light

GOSAT is a Japanese greenhouse-gas observation program involving JAXA, the National Institute for Environmental Studies and the Ministry of the Environment. The first satellite, Ibuki, launched in January 2009; Ibuki 2 followed in October 2018. The program combines spacecraft development, instrument operations, data processing and environmental research rather than assigning every function to one institution.

GOSAT-GW, archived as Ibuki-GW, launched in June 2025 with both the TANSO-3 greenhouse-gas instrument and AMSR3 for water-cycle observations. Sharing a spacecraft connects two observing capabilities, but it does not make their measurements identical. AMSR3’s microwave observations and TANSO-3’s gas-related measurements have different purposes and processing paths.

The original GOSAT’s TANSO instrument combined a Fourier Transform Spectrometer with a Cloud and Aerosol Imager. The spectrometer measured patterns in reflected and emitted infrared radiation. Gas absorption affects those patterns, allowing retrieval — open definition algorithms to estimate atmospheric carbon dioxide and methane. Cloud and aerosol information helps assess and account for conditions that affect the observed light.

A column-averaged mixing ratio — open definition describes a gas relative to dry air through a vertical atmospheric column. It is not simply the concentration beside a road or a direct count of emissions from the ground immediately below. A map may also combine observations from multiple times, with gaps where usable measurements are unavailable. Reading the product definition is part of reading the map.

GOSAT: distinguish the products

NIES distinguishes measured radiance products, retrieved concentrations and higher-level estimates of sources and sinks. Inferring fluxes requires atmospheric transport modeling and additional information, including meteorological and ground observations. Winds move gases away from their sources, so a concentration enhancement and an emission rate are related but different quantities.

For a fictional regional assessment, ask whether the displayed value is a concentration, a model-derived flux — open definition or a smoothed map. Inspect its time interval, uncertainty and supporting inputs before comparing regions. A blank area does not demonstrate zero emissions, and a high column value does not identify a unique facility by itself. The strongest explanation connects each claim to the particular product and the additional evidence it needs.