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Water Today Title September 18, 2021

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Satellite technology


By Cori Marshall

Water is essential, not only for human survival but as a cornerstone of our understanding of life itself. Recently a group of international scientists announced that within a group of recently discovered exoplanets, three could possibly be home to liquid water oceans on the surface. Being that water is at the core of our understanding of life, how much do we really understand our oceans and bodies of fresh water?

The Global Land-Ocean Temperature Index shows that average global temperatures have been steadily rising, and that the warmest ten years on record have occurred in the twenty-first century. NASA research shows that as water heats and expands making sea levels rise, this surface height indicates the amount of heat stored in our oceans. It is the heat stockpiled in our oceans that drives our climate.

The Surface Water and Ocean Topography (SWOT) mission aims to enhance our understanding of our oceans and terrestrial surface waters.

The SWOT Satellite and mission is a joint effort between NASA, the French Space Agency (CNES) and the Canadian Space Agency (CSA). NASA and CNES combined contributed $1billion. Each agency will be handling specific elements of the project.

CNES will supply the platform, memory storage capacity, and oversees testing the satellite. Most importantly CNES will be providing the radio frequency for the KaRin instrument - a Ka-band Radar Interferometer that will determine ocean and surface water topography. France is also in charge of supplying the dual frequency Ku/C-band Nadir Altimeter.

NASA, for their part, will be providing controls for the main instrument as well as the payload module. They will also be providing the radiometer and GPS accuracy. NASA will have the responsibility of testing the integrated payload and launch systems.

To gain a better understanding of the mission and the Canadian role we spoke with Robert Saint-Jean, a Senior Program Scientist at the CSA. Saint-Jean tells us that the mission will "monitor with very high accuracy the height of the ocean surface." Saint-Jean explains that the SWOT satellite will "send a microwave pulse toward the ground and listen with two separate antennas, it's like your two eyes so you can see in 3D."

The CSA contribution is the provision of an Extended Interaction Klystron (EIK). Klystron technology amplifies wavelength sensors on the satellite, much like focussing a camera lens. According to a press release the CSA recently awarded a $3.8 million contract to Communications & Power Industries Canada (CPI). Final delivery of the EIKs is set for 2019.

The total Canadian financial contribution to SWOT is $15.2 million, $17 million after taxes. While current data is used by a few oceanographers, the data that SWOT will collect is already generating interest amongst a much wider Canadian community of oceanographers and hydrologists. The $17 million dollar investment will benefit the Canadian scientific community as it will have "early access to SWOT data and scientific expertise", according to a CSA press release.

A reason for gathering this data is that the surface if the ocean is not uniform. Robert Saint-Jean explains that warmer water is higher in altitude than surrounding surface water, and sits approximately "70 centimetres higher". Saint-Jean states that research shows "that there is a lot of energy transfer between warm currents and surrounding water that affects the climate."

A benefit to Canada is a greater understanding of the mechanics of ocean and surface waters. Saint-Jean says that "changes in altimetry have a direct effect on the tides, on the local currents, on the eddies, along the coast and on the fisheries." Saint-Jean adds "in the context of climate change as we are observing right now, it is of critical importance that we understand these processes."

The technology used on this mission will bring our surface waters into clearer focus and will provide Sea Surface Height (SSH) data with a resolution of 15 kilometres above our oceans. According to the Hydrology Science Lead in France, Jean-Francois Cretaux, "rivers, lakes and oceans have never been measured like this". When considering the data that will be collected the excitement could be heard in Cretaux's voice when he said "it's amazing when you think about it. The project expects to generate seven terabytes of information [to be] downloaded every day."

The mission will generate a complete two-dimensional picture of our surface water in a very short time frame. Tamlin Pavelski, Hydrology Science Lead University of North Carolina, suggested that the satellite "will do one complete pass of the Earth every ten days". This rapid turn around is important in expanding our scientific knowledge, "imagine having new data, on how much water, where it is and the changes that you could learn of if you had new information every ten days" Pavelski added.

Floods caused by rising sea levels along coastal areas and from rivers and lakes cause damage to the environment and cities. The type of data that SWOT will gather, could have shown changing patterns in Canadian surface water, and quite possibly predicted the 2013 Alberta floods in High River and Calgary. This could have saved Canadians $1.7 billion.

SWOT's high resolution will allow for the "monitoring of the surface topography of lakes and rivers" says Robert Saint-Jean. As Canada is home to the highest concentration of fresh water bodies in the world Saint-Jean adds, "this is of very high importance for Canada". Saint-Jean continues that we do not have very good knowledge of these dynamics."

There are however limitations to what SWOT can accomplish. It is not able to monitor groundwater. "There is no penetration under the surface," says Saint-Jean.

According to Alfonso Rivera, hydro-geologist with Canadian Geological Society, "the breakthrough of SWOT [is that it] provides two-dimensional measurements of surface waters. This is a change from the way surface waters are measured currently." Rivera adds that water flow and storage are fundamentally a two-dimensional process in watersheds.

"But SWOT does not account for the groundwater aspects of an integrated surface water-groundwater approach. Other means must be used to incorporate groundwater measurements, he says. "The nature of groundwater flow and overall dynamics (recharge, discharge) stored in aquifers is fully three-dimensional and SWOT is not adapted to measure that nature. Our most current satellite applications include the use of the GRACE signal to assess groundwater dynamics at the scale of Canada," says Rivera.

Rivera adds "At large scales such as the complete landmass of Canada, space technologies have been playing a critical role in providing observations associated with various aspects of the water cycle." The challenge lies in amalgamating the data. Rivera continues, "the challenge is to foster the integrated use of multiple satellite datasets in water studies which will ultimately lead to a holistic understanding of the entire water picture."

Though SWOT falls short of collecting data on groundwater the knowledge it provides will be invaluable, not only to Canadian scientists, but to the global scientific community. The data collected will lead to a greater understanding of the processes. This greater understanding will foster greater preparedness, which will ultimately save lives. The SWOT mission is scheduled for launch in 2021.

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