JAXA Earth Observation Overview for measuring the Global Water Cycle
Authors: Oki Riko , Kubota Takuji , Kachi Misako , Yamamoto Kosuke , Yamaji Moeka 
Published: February 2023

Japan Aerospace Exploration Agency (JAXA) currently operates six Earth observation missions for water cycle and climate studies, disaster mitigation, and various application studies including weather forecasts. One of six missions, the Global Precipitation Measurement (GPM) is an international mission to achieve highly accurate and highly frequent global precipitation observations (Hou et al. 2014, Skofronick-Jackson et al. 2017). The GPM mission consists of the GPM Core Observatory jointly developed by U.S. and Japan and Constellation Satellites that carry microwave radiometers and provided by the GPM partner agencies. The GPM Core Observatory, launched on February 2014, carries the Dual-frequency Precipitation Radar (DPR) by JAXA and the National Institute of Information and Communications Technology (NICT) (Kojima et al. 2012, Iguchi 2020).&#160;Regarding future satellite missions, Global Change Observation Mission - Water "SHIZUKU" (GCOM-W) follow-on mission (AMSR3) with high-frequency channels (166 & 183 GHz) will be installed on the Global Observing Satellite for Greenhouse gases and Water cycle (GOSAT-GW) satellite (Kasahara et al. 2020). Japan will provide the world's first satellite-based cloud vertical motion information by the Cloud Profiling Radar (CPR) to the Earth Clouds, Aerosols and Radiation Explorer (EarthCARE), Europe-Japan joint mission (Illingworth et al. 2015, Wehr et al. 2023). JAXA is currently conducting R&D of the Precipitation Measuring Mission carrying the Ku-band Doppler Precipitation Radar to succeed and expand currently operating GPM/DPR.&#160;It is also required to evolve combined use of multi-satellite to provide the &#8220;best&#8221; information to users. Under the GPM mission, the Global Satellite Mapping for Precipitation (GSMaP) produces high-resolution and frequent global rainfall map based on multi-satellite passive microwave radiometer observations with information from the Geostationary InfraRed (IR) instruments (Kubota et al. 2020). Output product of GSMaP algorithm is 0.1-degree grid for horizontal resolution and 1-hour for temporal resolution. The GSMaP near-real-time version product (GSMaP_NRT) has been in operation at JAXA since November 2007 in near-real-time basis, and browse images and binary data available at JAXA GSMaP web site (http://sharaku.eorc.jaxa.jp/GSMaP/).JAXA also collaborates with model development community to expand satellite data utilization in various fields. With the goal of providing reliable water cycle information and achieving integrated water resources management, JAXA has developed the global hydrological simulation system &#8220;Today&#8217;s Earth (TE)&#8221; under the joint research with University of Tokyo (Ma et al. 2021). To provide the products with better accuracy, rainfall from the GSMaP is used for TE-Global GSMaP version. The Over 50 hydrological variables are now accessible through the web page and ftp site of the &#8220;TE-Global&#8221; system (https://www.eorc.jaxa.jp/water/).JAXA continues to provide useful satellite-based information related to the global water cycle.