Rice University creates open-access database of water isotopes from eight satellite missions

Rice University led an international team in building WISO-SAT, an open-access platform for hydrogen isotopes measured in atmospheric water vapor by eight satellite missions, with records running from 2002 to the present. Together the missions provide 24 years of observations, a rich dataset about where water comes from and the paths it takes around the planet.

The resource unifies two decades of observations into one standardized platform, and the team removed technical obstacles for scientists studying the global water cycle. Gridding measurements lets scientists compare datasets while accounting for instrument differences and locate each observation precisely on the planet. The public database is open to any researcher, who can compare observations across all eight missions and review how the team standardized the data. “The data is gridded and standardized,” said Mampi Sarkar, a Rice research scientist and corresponding author on the study.

The eight missions used independent designs, and their records resided in separate places with different instrument calibrations, spatial grids and sampling altitudes, creating serious data fragmentation in water isotope observations. Fragmented, incompatible data sets meant that reconciling even two datasets could take up to a year of cleaning and comparison before any analysis, and researchers around the world could unknowingly duplicate that work.

Sarkar said a large collection of water-isotope measurements already existed, but no straightforward way existed for a researcher to use it. Most scientists and missions want to share data, although each satellite answered somewhat different questions, so the data come in different formats even though they all measure the same thing.

Sarkar worked with specialists from NASA in the United States, Europe and Japan, each experienced with one satellite, which gave her access to that mission’s dataset and details on collecting and recording its data. After gathering the raw data, she reviewed it thoroughly to understand it and built a pipeline that standardizes and shares it.

The pipeline takes raw, heterogeneous satellite outputs and turns them into one gridded format, adjusting for the sensitivities of each sensor so researchers can compare measurements from different missions. The public dataset includes the pipeline, so researchers can grid and standardize comparable data before submitting it and contributing future observations to the open resource.

Water isotopes are water molecules whose masses differ slightly, and researchers treat them as location identifiers for determining where water comes from, because the molecules differ a little in mass. The balance of heavy isotopes to light isotopes is unique to where the water began and the processes it experienced, so the ratio reveals how water moves across the globe.

Sylvia Dee, a Rice associate professor in Earth, environmental and planetary sciences and one of the paper’s authors, said satellites reach regions field researchers cannot and provide consistent, long-term records for water-cycle science. The observations had to be treated as one dataset to create a trustworthy record of the full water cycle, she said. Dee’s National Science Foundation CAREER award supplied the project’s initial funding.

The research came out in Scientific Data as an open-access paper called WISO-SAT: A global database of stable hydrogen isotopes in water vapor from eight satellite missions. National Science Foundation grants 2338861 and 2513024 funded the research, as did NASA grant 80NSSC26K0676 for the Energy and Water Study Satellite and Precipitation Isotope Constrained Estimates.

Researchers can use WISO-SAT to study cloud formation, precipitation mechanisms, moisture transport, El Niño and La Niña, deforestation and soil moisture. Its continuous multi-decadal record supports work on atmospheric moisture transport over remote polar and oceanic regions where ground instruments cannot reach, and ecosystem and surface dynamics such as land-atmosphere feedback loops. The long-term data can assess how El Niño and La Niña drive changes in global atmospheric circulation patterns and can support high-resolution studies of localized evapotranspiration, soil-moisture depletion and hydrological impacts of deforestation.

Dee said the value of WISO-SAT comes not only from assembling the measurements but also from the work needed to prepare them so researchers, students and members of the public can use the data effectively, and she described projects like WISO-SAT as advancing science through cooperation, open access and data preservation. “There are so many things this data could be used for,” Dee said.