The SWOT measurement accuracy will be impacted by waves. The SWOT requirements will be met for significant wave heights of 2 meters. The Doppler effects from satellite motion will be compensated for using radar processing techniques on board the satellite.

We shared some information on the resolution side of things in our previous answer here. (EP)

SWOT will “see” areas of the Earth between about 78 degrees north and south latitude, so that is most of the surface water on land and in the ocean.

You can use the SWOT Swath Visualizer to see if your area of interest will be covered by SWOT. (MS)

SWOT will “see” much of the surface water between 78 degrees north and south latitudes on Earth.

We have a specific study area on the Nile river which you can read more about at https://swot.jpl.nasa.gov/applications/early-adopters/#AlexandriaU. (MS)

We'd love to do SWOT-style cubesats!

The biggest challenge here is that SWOT uses a very powerful radar with a big antenna. Miniaturizing this is no small feat, but we've been thinking about ways to leverage geostationary radars. There is also some existing work on miniaturizing the previous radar altimetry technology (from missions such as Jason, Sentinel 3, and others).

Look for the mission concept being developed by colleagues from the French Space Agency called SMall Altimetry Satellites for Hydrology (SMASH) which is designed to be a constellation of small satellites. (CD)

The current plan from the SWOT Science Team is to use river width together with the elevation of the water surface that will be directly measured by SWOT. We'll calculate the slope of the top of the river from measurements of elevation, and we'll infer changes in the cross-sectional area from joint changes in elevation and in width. However, this does leave a big unknown: the minimal (unseen) cross-sectional area.

We will make a best guess for that based on many months of data through fitting with a simple equation for hydraulics (Manning Equation). Everything we produce, including our estimates of river discharge, will come with an estimate of uncertainty.

And, of course, we'll be using ground measurements at selected locations around the Earth for validation. (CD)

We discussed SWOT's orbit a bit in this answer upthread.

SWOT provides continuous global measurements of the Earth's water bodies. The ocean circulation will be determined from the ocean height measurements at spatial resolutions of 15 km for 68% of the ocean.

Lakes, reservoirs and wetlands whose surface area exceeds (250m)^2 will be measured with a height accuracy better than 25 cm, and rivers whose width exceeds 100m will be measured with a height accuracy of 10 cm for 10 km sections of the river at a time. (EP)

SWOT data will be used to support model predictions of drought, which will help in monitoring these highly impactful events.

Models can be greatly enhanced through the integration of space-based observations (like SWOT and other satellites like GRACE-FO), as well as on-the-ground measurements, to improve observations and predictive capabilities. (MS)

Yes! The data will be publicly available for everyone to use.

Jan 2024 will be in the heart of the SWOT science mission, so it will be a great time to be looking at the data. (BH)

I think the strengths/opportunities and weaknesses/threats I see are connected to the same thing: the measurement SWOT is making is new!

This means there are new engineering and science challenges that must be tackled and solved to make the mission a success (which our capable team has been doing and will continue to do!).

But, this is also a strength and opportunity. SWOT is going to measure things over the land and the ocean we’ve never been able to see from space before. The potential for scientific discovery is huge, as is the potential usefulness of this data for communities across the globe. (BH)

The SWOT mission is actually a collaboration between NASA and the French Space Agency (called CNES), with contributions from the UK and Canadian Space Agencies. This is therefore very much a collaboration with international partners.

NASA, and other space agencies, already have multiple satellites that look at various components of Earth's freshwater. For example: soil moisture (SMAP), rain (GPM), snow cover (Terra/Aqua), elevation of the largest lakes and reservoirs (Sentinel-6 Michael Freilich), and extent of lakes and reservoirs (Landsat, Sentinel 1, Sentinel 2).

What makes SWOT so special for Earth's freshwater reserves is that it will measure the elevation of water and the extent of water bodies at the same time. And it will do so for many more rivers, lakes, reservoirs and wetlands than we've ever seen before. That means we'll know where the water is and where it's going like we've never known before. SWOT will also see the Earth's saltwater (like the oceans) in a much more detailed way than we've ever done before, and that will help us to understand ocean currents.

If we could speak with turtles, we'd tell them how to use this knowledge for a quick ride back to Hawaii, but I think they've already figured this one out! (CD)

The SWOT mission was initially recommended in 2007 in a report by the National Research Council (NRC) called “Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond” for implementation by NASA.

SWOT, like many other NASA and international satellite missions, is a science-focused mission but will have many ancillary benefits to society that extend beyond the research objectives of the mission!

Some of the areas of societal benefit for SWOT include improved flood forecasting and better water resource management through monitoring of changes in water levels of reservoirs and in better knowledge of river discharge. Forty percent of the global population lives within 100 km of the coast, and SWOT will provide better quality data closer to the coasts that can feed into models for improved forecasts of the state of the ocean and some extreme events that may impact people living at the coasts. It will also provide critical information for fisheries management practices and safety at sea.

You can read more about these at https://swot.jpl.nasa.gov/applications/applications-areas/. (MS)

The SWOT orbit has an average revisit time on the order of approximately 11 days at low latitudes. This temporal sampling is similar to that obtained by previous ocean altimeter missions. It also allows appropriate sampling of river dynamics in the tropics. At high latitudes, the sampling will produce shorter revisit periods, compatible with arctic river dynamics. This temporal sampling choice is a trade-off for maintaining global coverage including the high-latitude regions and for minimizing the tidal aliasing.

SWOT will allow global measurements even in remote areas that are not easily accessible, which is not feasible with ground surveys. Measurements of the the global storage change in terrestrial water bodies at sub-monthly, seasonal, and annual time scales will provide insight into important questions such as the temporal and spatial scales of the hydrologic processes controlling fresh water storage and transport across the world's continents, as well as the impacts of humans on fresh water resources.
(EP)

Data from NASA satellites is used in many aspects of land and water management by operational agencies in the U.S. and internationally. We are a data and information resource for these agencies, but we are not, for example, in the business of doing water management. This information will be able to support planning for dam operations.

You can learn more about one specific example of how SWOT data may be used in Egypt in this way at https://swot.jpl.nasa.gov/applications/early-adopters/#AlexandriaU. (MS)

SWOT is going to provide some cool things over the ocean. First, it will measure closer to the coast than our other satellites. This will provide an improved understanding of how sea levels are rising and allow us to improve models for things like storm surge.

Second, SWOT is going to measure smaller scale features in the ocean. 90% of the excess heat trapped in our atmosphere gets absorbed by the ocean. We think that much of that heat is absorbed by the smaller scale, short-lived ocean features like fronts and eddies. SWOT will collect data on these ocean features and help us understand how the climate is responding to ongoing warming.

Understanding these features and ocean currents better will have benefits for shipping and navigation. (BH)

There is no conclusive evidence that it is raining more over the ocean than it has in the past. Understanding how the global water cycle and precipitation patterns are changing under a warming climate is really important for both scientific and societal reasons.

While SWOT won't give us all the answers, the measurements it provides and its ability to measure almost all of the surface water on Earth (land and ocean) will support brand new insights and scientific discoveries.

The data from SWOT will be publicly available and scientists will be able to explore the SWOT "data sandbox", yielding new and unexpected discoveries. (BH)

SWOT will just measure surface water. The data from SWOT will be publicly available and will have many positive benefits by allowing people to track changes in water over time and manage water resources more effectively.

Personally, I'm most excited about what SWOT will tell us about the changes in the ocean close to the coast. Our other satellites that measure sea level are not able to get as close to the coast as SWOT will be able to, and there is a great deal we can learn about the response of sea level to climate change. (BH)

Yes! The scientific engine of the SWOT satellite, the Ka-band Radar Interferometer (KaRIn) instrument, will measure the height of water in Earth’s lakes, rivers, reservoirs, and the ocean.

To do that, KaRIn will transmit radar pulses to Earth’s surface and use two antennas to triangulate the return signals that bounce back. Mounted at the ends of a boom 33 feet (10 meters) long, the antennas will collect data over two swaths of Earth’s surface, each of them 30 miles (50 kilometers) wide and located on either side of the satellite.

KaRIn will operate in two modes. A lower-resolution mode over the ocean will involve significant onboard processing of the data to reduce the volume of information sent during downlinks; the higher-resolution mode will be used mainly over land to look at freshwater. (BH)

The radar signal will not penetrate through the water, so we won't be measuring how deep the water is, just how high the surface of the water is.

Knowing the shape of the land underneath the water (the bathymetry) still remains a mystery except for some pristine water bodies which are very clear and for which the bottom can be detected with other satellites like the Ice, Cloud and land Elevation Satellite (ICESat-2). (CD)

The KaRIn radar instrument operates at the Ka-band frequency: so the signal that bounces back from the ocean, rivers, and lakes is much stronger than the signal that's reflected from land.

Using image processing techniques, the SWOT team is developing algorithms that will be able to differentiate between different surface types. (EP)

SWOT will measure 90% of the surface water on Earth. It won't measure the water that is at a higher latitude than 78 degrees North or 78 degrees South.

It also won't be able to measure very small lakes (smaller than 15 acres) or small rivers (narrower than 330 feet, or 100 meters). (BH)

SWOT is designed so that the signal that it sends bounces off the surface of liquid water, like the top of a lake, a reservoir, a river, a wetland, or an ocean, and eventually returns to the satellite. That same signal does not reflect off of land or ice.

What this means is that the information that comes back to the satellite is about liquid water that we can see on Earth's surface. For liquid water that is underground (groundwater), we have another mission called the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission. GRACE-FO measures gravity changes on Earth, and because water is so heavy, we can observe any changes in groundwater using those gravity measurements.

For solid water that is on top of the surface (ice caps), we have another mission called Ice, Cloud and land Elevation Satellite (ICESat-2). -CD

The SWOT satellite includes a novel instrument called KaRIn (Ka-band Radar Interferometer) that enables measurements of water height with an order of magnitude better resolution than current satellites.

This precise measurement requires advanced radar processing techniques that in the case of KaRIn are done on board the satellite, as compared to previous satellites that downlinked the collected data to be analyzed on the ground. This processing reduces the amount of data that has to be transferred from the satellite to the ground.

Even so, SWOT produces an unprecedented amount of data to achieve a global measurement of Earth's water. -EP

Yes! You can find the latest at swot.jpl.nasa.gov or follow us on social media @NASAEarth and @NASAJPL (on Twitter, Instagram and other social platforms).

SWOT is scheduled to launch in December from Vandenberg Space Force Base in California.

Great question!

SWOT will not be able to ‘scan’ the seabed, per se. SWOT will only measure the surface height of the ocean.

However, the surface height is not independent of the shape of the sea bed (or, the “bathymetry” of the ocean). Some geophysicists who study ocean bathymetry can use SWOT and other satellites that view what we call the surface topography of the ocean to infer the shape of the sea bed. (MS)