EARLY RESULTS OF THE ADVANCED MICROWAVE SCANNING RADIOMETER 3 (AMSR3) PART2: ALGORITHM AND VALIDATION

M. Kachi¹, R. Shimada¹, E. Yoshizawa¹, K. Ohara¹, K. Aida¹, K. Nakata¹, T. Suzuki¹, K.Inaoka¹, T. Miura¹, Y. Kojima¹, N. Ebuchi²

¹Japan Aerospace Exploration Agency, ²Hokkaido University

The Advanced Microwave Scanning Radiometer (AMSR) series is a series of Japanese microwave imager that has unique capabilities in its high spatial resolution with large-sized main reflector (~2-m diameter), dual polarization channels for all frequency bands from 6.9 to 89 GHz, and frequent global observation with wide swath more than 1500-km, to obtain water-related information inside clouds and at the Earth’s surface through clouds. Major mission targets of the AMSR series are: 1) monitoring and prediction of water cycle variations; and 2) operational applications. It continues global water cycle observations more than 23 years by previous two missions, AMSR-E on board the NASA’s Aqua satellite launched in 2002 and AMSR2 on board the Global Change Observation Mission – Water (GCOM-W) launched in 2012.

The Global Observing SATellite for Greenhouse gases and Water cycle (GOSAT-GW), which carries AMSR3, the latest sensor of AMSR series, was successfully launched at 1:33 on June 29, 2025 (JST) from the JAXA Tanegashima Space Center by H-IIA rocket #50 (final flight) and entered its nominal operational orbit on July 20. AMSR3’s main reflector was set to rotate at a speed of 40 revolutions per minute to ensure stable observations, and AMSR3 started collecting observation data as part of the satellite’s initial functional verification activity since August 11. First images from AMSR3 were released to public on September 5. Upon successful verification during the Initial Functional Verification Operations phase, which is planned to take 3 months after the launch, JAXA will conduct the initial calibration and validation of AMSR3 data and make transition to the nominal observation operation. For the calibration of AMSR3 Level 1 brightness temperature and validation of Level 2 geophysical parameters, we will make an adjustment of Level 2 algorithms that were developed based on that for AMSR2 and verify the product accuracy for public data release. Those activities will be conducted in cooperation with our partner agencies, universities, and institutes. We use data from in-situ networks operated routinely, or satellite observations in case of difficulty in obtaining in-situ data, for validation. In addition, we operate ground observation sites for soil moisture in Mongolia since 2000 and in Australia since 2012, and plan to establish new ground observation site for snow depth in Canada in fall 2025. Early verification results of AMSR3 standard products will be presented at the meeting.

AMSR3 succeeds in afternoon orbit observation of AMSR2, which is currently operation in orbit, and expands its observation capability to respond to new user needs. Major improvements in AMSR3 are new high-frequency channels (166- & 183-GHz) for snowfall retrievals and water vapor analysis in numerical weather predictions, and additional 10.25-GHz channels with better NEDT for robust sea surface temperature (SST) estimates. We will distribute new products, including solid precipitation and 10-GHz SST, as well as existing products to keep continuation from AMSR2.

While public data release of AMSR3 is scheduled after the completion of initial calibration and validation phase (1-year after the launch), JAXA plans to distribute early data to partner agencies to enable preparing implementation of AMSR3 data in their operational applications.