September 2, 2026 (JST)

Japan Aerospace Exploration Agency
Japan Meteorological Agency

 In June 2025, the Japan Aerospace Exploration Agency (JAXA) successfully launched the Global Observing SATellite for Greenhouse gases and Water cycle “IBUKI GW” (GOSAT-GW). “IBUKI GW” (GOSAT-GW) is a polar-orbiting satellite that observes the Earth as it travels in a north-south direction, and the Advanced Microwave Scanning Radiometer 3 (AMSR3) mounted on this satellite globally observes microwaves naturally emitted from the Earth’s surface, water vapor in the atmosphere, clouds, and precipitation including snowfall, thereby capturing a wide range of information related to the water cycle. JAXA and the Japan Meteorological Agency (JMA) have jointly advanced surveys and technological development for the early and effective utilization of AMSR3 observation data.
 As a result, it was confirmed that the use of AMSR3 data improves the accuracy of water vapor analysis and prediction, which is important for understanding atmospheric conditions, in the numerical weather prediction (NWP)Systems^*1 that underpin the weather forecasts issued by JMA, and is expected to improve precipitation forecast accuracy. Following this confirmation, JMA will begin using the data on September 8, 2026. For details, please refer to the attached document.
 In addition, JMA has already begun using AMSR3 data in its sea surface temperature and sea ice analyses, and the resulting analyses are being utilized as basic information for monitoring sea conditions and sea ice, promoting the fisheries industry, and selecting safe and efficient shipping routes for vessels.
 JAXA and JMA will continue to devote efforts to conduct research and development aimed at making more effective use of valuable satellite observation data.

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 The Japan Meteorological Agency (JMA) operates the NWPsystems that serves as the foundation for the issuance of weather forecasts and disaster prevention meteorological information, including advisories and warnings. NWP forecasts future atmospheric conditions by dividing the Earth's atmosphere into fine grids, assigning values such as wind, temperature and water vapor content to each grid, and using computers to calculate how those values change over time based on the laws of physics. For forecast calculations, it is important to provide as accurate a representation as possible of the state of the atmosphere at the start of a forecast (known as the initial conditions), and the accuracy of these initial conditions has a major impact on forecast accuracy. For this reason, the use of a wide range of meteorological observation data, including satellite observations, is indispensable in generating initial conditions.
 Microwave radiometers can continuously observe, on a global scale and regardless of day or night, information on the Earth’s surface (land and sea), atmospheric water vapor and clouds, and precipitation, including snowfall. JMA has thus far used observation data from the Advanced Microwave Scanning Radiometer (AMSR) series, mounted on JAXA’s Earth observation satellites, in the NWP Systems. These data also contribute to improving the accuracy of precipitation forecasts by enhancing the accuracy of analysis and prediction of water vapor distribution. The AMSR3 instrument aboard the Global Observing SATellite for Greenhouse gases and Water cycle "IBUKI GW" (GOSAT-GW), launched in June 2025, is the successor to the AMSR2 instrument aboard the Global Change Observation Mission - Water "SHIZUKU" (GCOM-W) satellite, launched in May 2012. AMSR3 includes newly added channels in frequency bands that provide information on water vapor in the mid- to upper troposphere, and further improvements in the accuracy of water vapor analysis are expected.
Figure 1 shows an example of improved precipitation forecasting through the use of AMSR3 data. Compared with the observed precipitation area over southwestern Hokkaido between 3:00 a.m. and 6:00 a.m. on September 7, 2025 (JST) (JMA’s Radar/Raingauge-Analyzed Precipitation) (Figure 1(a)), forecast without use of AMSR3 data showed an underestimation of precipitation (Figure 1(b)). On the other hand, the forecast using AMSR3 data showed improvement (Figure 1(c)). It is considered that the use of AMSR3 data improved the analysis and forecast accuracy of atmospheric water vapor, thereby improving precipitation forecasting.