SWOT Satellite Launched: How Much Water Is There in the World?

Water covers about two-thirds of the Earth. Almost everything is salt water – but there is hardly any data for fresh water. The SWOT satellite uses modern radar technology to show the amount of water in the area.

“There is an old saying, ‘You can’t control what you can’t measure.’ That’s why we need to measure this precious resource!” With this rippling “precious resource,” Cedric David of NASA’s Jet Propulsion Laboratory (JPL) simply means – Water: water in rivers, water in lakes, water in oceans.

Fresh water is also recorded

“We usually quantify the amount of water like this,” he further explains: “You put a stick or a ruler in the water and you measure how high the water is. If you add that measurement to the nature of the water basin, you can determine how much water is there and maybe how fast it flows.”

The researchers thought it must be faster these days – preferably from space. That’s where SWOT, short for Surface Water and Ocean Topography Mission, comes in. This is the first satellite to measure not only oceans, but also rivers and lakes, in short: liquid water all over the world. “This means we won’t miss any more water resources,” hopes Chris Aceves, chief engineer on the mission at the Jet Propulsion Laboratory in Pasadena, California.

Measure all water resources every three weeks

We are the scientists on earth. And Acevis adds that SWOT is pretty big. “Think of a satellite as a school bus – that’s about the same size. “Together with the side solar panels, it is about the size of a medium-range Boeing 737. It weighs about two tons. This block will be a Falcon 9 launch vehicle by the American space company SpaceX in California in Earth orbit at an altitude of about 850 kilometers. From there, the satellite creates a complete picture of all the water resources on the blue planet every 21 days for at least three years.

These measurements should not be an end in themselves. Because when it comes to water, astrobiologists always get a tear. “Water is essential to life,” asserts David. “When NASA looks for life on other worlds, one of the first clues is always the possibility of water.” The equation applies: no life without liquid water. Earth is the best example of this.

The only break is fresh water

But even on their home planet, researchers don’t know exactly how much water there is and how it’s distributed. They estimate that there is between two trillion liters of water on Earth. Almost all – with the exception of two or three percent – are salt water.

Scientists would like to know more about it. SWOT is designed to measure all the water on Earth that can be seen from space. For the first time, geologists are given information about the amount of water resources. They will be able to understand the impact of weather and climate on oceans, rivers and lakes.

Radar beams from space

The mission is a joint project of the US, Canadian, British and French space agencies. It should be able to do more than earlier radar measurements of bridges or sticks in water in the Middle Ages: There is radar on the satellite that sends its beams to the surface of the water. It operates in a frequency band that gives clear information about whether the radar beams hit water or another surface.

The time that elapses between sending and receiving the reflected signal will tell researchers how high the water level is at a particular location. “If we combine this information with our data about the width and current behavior of the river, we can estimate how fast and how much water is flowing there,” says David.

SWOT measures non-stop

And because it is the radar beams that SWOT sends to the ground, that is, the satellite does not take any visual images, there are no limits to its measurements. About 70 percent of the Earth is covered in clouds. And half the planet is in darkness. But radar beams don’t care if it’s day or night or whether clouds obscure the view. You can simply walk in and measure the desired area at any time. The area that the satellite will observe from space covers nearly 100 percent of the Earth’s surface.

During runtime, scientists also want to pay attention to possible changes in measurement results, namely whether the amount of water has increased or decreased in a place, whether lakes have dried up or coastal landscapes have changed. The view from space should record all of this.