Feature | February 22, 2023

SWOT's eyes over Earth's surface water

SWOT's Program Scientist, Nadya Vinogradova Shiffer was interviewed by Yanhua Chen for Nature Water. The original journal article can be found here: (link)

The Surface Water and Ocean Topography mission, known as SWOT tracks Earth’s surface water with unprecedented accuracy and completeness, improving our understanding of water under the changing climate. Nadya Vinogradova Shiffer is program manager of Ocean Physics, lead of Climate Variability and Change at NASA headquarters, program scientist of SWOT and co-founder of a non-profit organization for research in Earth science. In her conversation with Nature Water, she speaks about what SWOT will bring and why SWOT matters.


What does SWOT measure?

SWOT is a water mission. It measures the height of almost all surface water on our planet. In one mission, SWOT will monitor the ocean, the land and freshwater resources, covering the entire water supply-demand chain. There is so far no other mission providing information as such. The excitement about SWOT is to build a new community of water scientists that will look at the Earth’s surface water in its entirety and movement, from ocean to land and back as a complete system using SWOT’s global coverage. This global and complete view of water will help us better describe and predict the water cycle and its deviations from the norms such as floods and droughts.

Another advantage of SWOT is its very high definition, the so-called ‘SWOT-goggle effect’ that brings blurry views of Earth’s water into focus, revealing new details. It’s like watching your favourite movie on an HD or 4 K screen after an old VHS tape. This highresolution view will enable monitoring rising seas in close proximity to the coasts and coastal cities, or seeing dynamic features in the open ocean, which act like effective engines that transport a large quantity of heat, energy, oxygen, and nutrients. These are all climate-relevant properties that help us understand and predict future climate. And when SWOT flies over land, you would see the volume and storage of freshwater resources in lakes and rivers with more clarity and definition. As our hydrologists call it, SWOT is a great equaliser. Some regions have limited ground observations, and sometimes it’s impossible to access water data. SWOT would be this equaliser that helps solve this problem, providing unified high-quality water data around the world.

SWOT is unique in many ways. How is it different from other Earth missions that monitor water, for example, the Gravity Recovery and Climate Experiment (GRACE) mission?

GRACE, another mission that NASA flies jointly with international partners, is of great relevance to hydrology and water in general. GRACE has proven valuable for groundwater monitoring. SWOT, on the other hand, will add the surface water component. GRACE measures changes in gravity, from which we infer the mass of water and its change. With SWOT, we will measure the height and calculate the volume. If you’re interested in flood prediction on land, it’s not enough to know its extent. It matters to know how high that flood is. That’s highly important for stormwater management and disaster response. The height of the water is an unique dynamic observable. Over the ocean, knowing the height of the water and the slope of the ocean surface, we could derive how dynamic the water is, how it moves, and how it transports key climate variables like Earth’s heat, energy, and nutrients, or plastic and pollution.

SWOT will provide detailed and accurate information to understand water, energy and climate, and that means an enormous amount of data. How will the data be managed and calibrated?

It is undoubtedly an enormous amount of new data that we’ll receive. Even with its hybrid approach of onboard pre-processing coarser ocean data and fully-focused processing land data, SWOT will triple the amount of data that NASA’s Earth missions are currently providing. This realisation was essentially a catalyst for NASA to move towards commercial cloud solutions for data storage, redesign the data management systems, and broaden the Agency’s definition of open science. As a trailblazer of NASA’s transition to open science, the SWOT community completely redesigned data science systems and built a set of open-source tools to help future users transitioning to this new way of doing science.

Calibration is no easy task. To ensure that SWOT will be able to provide credible and robust information, we lined up several field campaigns to compare SWOT observations with ground data on land, on lakes and rivers, on coastal environments, and on open ocean. More than 50 campaigns are now planned worldwide for gathering ground-based measurements, supported by a large international community. It is remarkable how scientists from both hemispheres are coming together and, in some cases, contributing in-kind to collect ship-based and land-based measurements that will help validate SWOT new observations during the calibration phase of the mission. Such mobilisation of the international science community is unique and is another testament of the widespread excitement around SWOT.

When can we expect the first validated data for use?

As a pathfinder mission, SWOT will undergo a rigorous calibration and validation phase, during which it will fly at a lower altitude of 857 km in a repeated one-day orbit to assess mission performance. Taking advantage of ground data from all that 50+ field campaigns during the daily sampling phase is critical to the mission success. During this phase, our calibration and validation team will dive deep to see how well the system performs and compare it with in situ observations. Beyond mission calibration, the daily-sampling phase also presents a unique opportunity to study rapidly evolving phenomena. What a treat to have a daily show of Earth’s water for 6 months! Once the calibration phase is complete, we will boost SWOT into its higher orbit of 891 km to collect water height measurements every 21 days, on average.

While our original requirement was to deliver validated datasets a year after SWOT’s launch, NASA and Centre National d’Etudes Spatiales (CNES) are piloting a new approach to distribute data and share pre-validated datasets earlier with the science community. This is open science in action, where we invite the wider science community to actively participate in SWOT’s validation phase and help us deliver science-quality and Nature-publication ready datasets. If you are interested in peeking at new data and lending your expertise, please join us. It’s time to have all hands on deck!

Will SWOT help achieve the Sustainable Development Goals (SDG) goals? What is your experience of harnessing science for decision-making?

For sure, the information and knowledge derived from SWOT data is expected to inform a wide range of societal applications, operational activities, and decision-making that include any water-related management. For example, water resource management, reservoir operation, flood management, ecosystem service planning, wetland monitoring, hydropower and navigation, fisheries, coastal protection, marine shipping, and other SDG-relevant sectors that involve water — fresh or salty. Translating science into solutions is a challenge. However, from our past experiences and positive examples related to water, sea level and SWOT, it is necessary to work with those who are looking for such information, jointly develop this information and package the science in a way that is more useful in their decision-making process. We established the SWOT Early Adopters programme to reach out to water resource managers, floods and risk managers, and had a dialogue between the scientists sharing what this mission is about and asking the users “how does this mission can help you in your daily job?”. We held a series of workshops to prepare various stakeholders to use SWOT data on day one, who were prepared to incorporate the data for multiple SDG-related applications, from stream flow and flood prediction to water management and increased coastal resilience.

SWOT is a collaborative, multinational effort. What’s your experience with such global partnerships, and how do you envision this?

NASA and CNES have been in the altimetry marriage for over 30 years, and many US and French scientists in our community have been working together for decades, knowing each other’s families, and exchanging Christmas cards. It’s a beautiful relationship. SWOT is a continuation of the NASA/CNES open marriage, and we are making new friends along the way. SWOT is a partnership of space agencies from four countries — USA, France, UK, and Canada, all contributing key hardware to the mission and supporting science objectives of SWOT. Building SWOT was a long road with a 20-year history. Taking this road with old and new friends made it possible to go from a concept to a launchpad.

I believe Earth observing business is a truly global enterprise. No one nation can accomplish a comprehensive look at our planet. Achieving success requires forming alliances and collaborations. Everyone has a role to play while working together for the common goal of learning about Earth as much as possible. I’m grateful to work with wonderful partners across the globe and look forward to our next adventures together.

What are the plans of NASA for future Earth missions?

There are several Earth missions in the pipeline over the next decade, adding to NASA’s prolific Earth-observing satellite fleet. PACE (Plankton, Aerosol, Cloud, ocean Ecosystem), is scheduled for launch in 2024. It will enhance our understanding of the ocean and atmosphere, ocean biology, carbon exchange, ocean health and ecosystems. We, water geeks, anticipate a lot of synergies between SWOT ocean eddies and PACE phytoplankton studies. Another mission on the 2024 horizon or so is called NISAR, for NASA-ISRO SAR mission, which will monitor Earth surface, its movement and change, with implications for various natural hazards like volcanic eruptions, earthquakes, or landslides. In 2025, another international water and sea level mission is on the books, Sentinel-6 B, which will extend what we call a ‘reference’ sea-level record to its fourth decade. From 2028 onward, NASA with a number of international partners is working to launch a set of four Earth missions that we call Earth System Observatory to monitor a wide range of atmospheric, land, and cryospheric processes. Exciting times to be a NASA Earth scientist!

Interviewed by Yanhua Chen