GIScience & Remote Sensing

HY-4A: Pioneering Global Ocean Salinity Mapping from Space

The successful November 14, 2024 launch of HY-4A, the inaugural satellite of the Chinese Ocean Salinity Mission (COSM), marks a significant advancement in space-based oceanography. As a key component of China's civil space infrastructure, HY-4A carries a sophisticated payload suite including the L-band Aperture Synthesis Microwave Radiometer (LASMR) and the Microwave Imager Combined Active and Passive (MICAP), which integrates L, C, and K-band radiometry with an L-band scatterometer. The mission delivers global sea-surface salinity (SSS) measurements with a targeted accuracy of 0.1 psu, establishing unprecedented capabilities for monitoring ocean salinity as a critical indicator of climate studies and the global hydrological cycle.

This Article Collection aims to document the initial scientific and technological achievements of HY-4A's first operational year, with specific focus on the synergistic utilization of its novel payloads of the LASMR and MICAP instruments. It solicits contributions concerning innovative strategies for the following categories, in the hope of establishing a framework for quantifying the mission’s contribution to global Earth observation:

• Radio-frequency interference mitigation
• Advanced instrument calibration methodologies
• Next-generation retrieval algorithms for sea-surface salinity, soil moisture, and related geophysical parameters
• Comprehensive validation through cross-comparative analyses with in-situ networks and complementary satellite missions such as SMOS and SMAP

Article Collection Guest Advisors

Wu Zhou received a B.S. degree in photogrammetry and remote sensing from Wuhan University, Wuhan, China, in 2004 and a M.S. degree from the National Satellite Ocean Application Service, Beijing, China, in 2007. He is currently a Researcher with the National Satellite Ocean Application Service, where his work is primarily engaged in the ground system design for the HY-2B satellite and the Chinese Ocean Salinity Mission (COSM) satellite. His research focuses on microwave radiometry data calibration, processing, retrieval, and validation.

Hao Liu received a B.S. degree in information science and electronic engineering from Zhejiang University, Hangzhou, China, in 1999, and a M.S. degree in aerospace vehicle design and the Ph.D. degree in computer application technology from the Graduate University of Chinese Academy of Sciences, Beijing, China, in 2002 and 2011, respectively. In 2005, he was an International Trainee with the European Space Agency, Noordwijk, the Netherlands. He is currently a Research Professor at the Key Laboratory of Microwave Remote Sensing, National Space Science Center, Chinese Academy of Sciences. His research focuses on microwave radiometry for Earth observation. Dr. Liu has proposed several novel payload concepts, including the Geostationary Interferometric Microwave Sounder (GIMS) for atmospheric sounding and the Microwave Imager Combined Active and Passive (MICAP) for simultaneous measurement of sea surface salinity, temperature, and wind speed. Since 2020, he has served as the Chief Designer of MICAP and the Deputy Chief Designer of the Chinese Ocean Salinity Mission (COSM) satellite. Following the successful launch of COSM in November 2024, he continues to lead post-launch calibration and data processing activities for the MICAP instrument.

Yinan Li received M.S. and Ph.D. from Xidian University, Xi’an, in 2010 and 2023, respectively. He is a Professor at the China Academy of Space Technology (CAST) in Xi’an. His research interests include system design and calibration for spaceborne microwave remote sensing instruments. He has successfully participated in developing microwave radiometers for the FY-3 and HY-2 satellite series. As the chief designer, he was fully responsible for the end-to-end development of the L-band Aperture Synthesis Microwave Radiometer (LASMR) payload carried on the Chinese Ocean Salinity Mission (COSM) as well as the processing and validation of its on-orbit data products.

Rong Jin received the B.S., M.S., and Ph.D. degrees in the Department of Electronics and Information, Huazhong University of Science and Technology (HUST), Wuhan, China, in 2006, 2008 and 2012, respectively. He was a postdoctoral scholar in the Department of Computer and Information Science at University of Michigan - Dearborn from 2012 to 2014. He is now an associate professor in the Research Center of 6G Mobile Communications, School of Cyber Science and Engineering at HUST. His research interests include microwave remote sensing, array signal processing, electromagnetics, and physical layer wireless network security.

Yili Zhao received the Ph.D. degree from the Ocean University of China, Qingdao, China in 2011. From 2011 to 2019, he has been with National Ocean Technology Center, Tianjin, China. During 2017-2018, he was a visiting scientist in the Spatial Oceanography Laboratory at Ifrermer, France. He is currently an assistant professor with Jiangsu Ocean University. His research interests include ocean remote sensing, with a focus on the calibration and validation of spaceborne microwave radiometers and on monitoring tropical cyclones using a combination of active and passive sensors.

Tianjie Zhao received the B.S. and Ph.D. degrees from Beijing Normal University, Beijing, China, in 2007 and 2012, respectively. From 2010 to 2012 he was the Director of the Laboratory for Earth Observation of Water, and a Principal Researcher with the State Key Laboratory of Remote Sensing and Digital Earth, Aerospace Information Research Institute, Chinese Academy of Sciences (CAS), Beijing, China. His research interests include microwave remote sensing and Earth observation of the water cycle. Dr. Zhao was the recipient of the Young Scientist Award from the International Union of Radio Science (URSI) in 2014, the Young Scientist Award from Progress in Electromagnetics Research Symposium (PIERS) in 2018, and the Li Xiaowen Youth Award in Remote Sensing Science in 2023.

Submission Instructions

Please review the journal scope and author submission instructions prior to submitting a manuscript.

The deadline for submitting manuscripts is 30 November 2026

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The Guest Advisors have declared no conflict of interests relating to their involvement with this Article Collection.