 It's again just a bit of history on so I'm going to be talking about the SWAT satellite mission that's planned to launch in 2021 and again, it was recommended from the decadal survey in 2007 NASA in connection with the French Space Agency started developing the mission and the big objectives for the SWAT satellite Provide global inventory of surface water bodies and characterize storage changes and river discharges So there's a hydrology component, but it's also going to fly over the ocean. So there's an oceanography aspect looking at mesoscale and submesoscale circulation so I'm going to focus primarily on the terrestrial side for the hydrology aspects related to groundwater Again, it's right now. It set the launch in fall of 2021 out of Vandenberg Air Force Base and SpaceX is actually going to launch the satellite And what it's going to do is it's going to measure rivers and water bodies And I'm going to drop all the ocean stuff for this talk But rivers wider than roughly 50 to 100 meters In width and water bodies somewhere between 100 and 250 meters by 100 and 250 meters in extent So the actual measurements will get from the satellite our water extent water surface elevation the back scatter from the water surface as well as the slope of the water surface and The orbit and this is where it gets a little different from some of the other satellites that I work with at least It's a 21-day near global Orbit and so every 21 days it repeats its exact cycle But because it's a wide swath altimeter system you get multiple hits in a particular location depending on Where you are based on latitude, which I'll show more in a little bit And so what's novel about SWAT relative to what we have today is you're going to get the surface Extent and the elevation at the same exact time. So right now we have altimeters that are given elevation of water and We have things like Landsat and other sensors are giving us water extent, but we don't have them merged together So the simultaneous measurement as well as the resolution so the resolutions are going to be quite good relative to what we have now So for water surface elevations, we're looking at you know less than 10 centimeters for the vertical accuracy widths plus or minus 15 percent for river widths and then slopes are 1.7 centimeters per kilometer is the so the mission targets It's a three and a half year mission With the first half of the year is dedicated to getting it up and running and then a three-year science mission So hopefully we'll get a three-year stream of data at least It's going to be a little challenging to work with some of the data We're talking about terabytes of data per day for the life of the mission So everything is migrating to a cloud-based system for working with the data looking at the data analyzing the data And relative to you know to this group I think the the derived discharge product is probably the most Interesting as well as the water levels in the rivers But the idea is if we see change like we're going to go over a river go over river You're going to see the extent you're going to get the slope you're going to see the elevation and so we can look at The changes in an area But what we'll never see It's hard to see in this figure here Is the actual bathymetry below whatever low elevation the satellite's going to see so There's going to have to be some assumptions on the missing bathymetry piece and roughness But once we have those and we've got some methods that do that we can then estimate a river discharge from that This is just giving you a sense of the rivers that we're going to see so again, you know, it does have some limitations It's 50 to 100 meter wide rivers and this is just a general Value drain roughly 2000 square kilometers, so it's not all rivers the world that we're going to be monitoring. It's your larger rivers But in terms of surface extents, I think this figure showing something like 400,000 square kilometers of water surface terrestrial site is going to be monitored and This is getting at the repeat visit You can see the global average is is every 11 days you're going to get a measurement You get more at the poles than you do at the equator, and I think the best way to look at this is I Don't know if it shows up very well This is an example in the Mississippi and so looking at 450 stream gauges over the 21-day orbit the highlighted and blues are the ones that are getting hit on particular days and I'm going to pull out two gauges and as an example for this in a second But this is just looking at the Mississippi basin those gauges. You can see of this a frequency distribution of Samples most of the gauges are getting hit twice every 21 days So it's not like weekly, but it's you know It's you know a couple times every 21 days and if we look at this next figure. I'm just pulling out two examples The top one and the bottom one and it's the actual USGS flow with the sampled SWAT data And then we have one with uncertainty on it But might the point at the bottom is really the highlight The one site's getting hit three times per 21 days the other side's getting hitting twice per 21 days But the spacing of the measurements are not uniform so the top gauges on day 8 19 and 20 So you're getting two back-to-back days, and then one at day 8 So it's a it's a strange spacing of the samples that are going to be a little challenging for people to think about initially And then the point of this is the based on some again hasn't flown yet, so I only have synthetic data We think we can do a really good job fitting the stream flow distributions Maybe not the day-to-day variability, but the distribution of flow And this other figure I'm just showing here is the the quantiles So based on the flow distributions that we fit with the synthetic SWAT data We can estimate the quantiles fairly well, and so we think we can get a pretty good Understanding of the basics of the flow distribution characteristics at these various gauges Which brings me to the summary here So again SWAT is going to see these rivers if you want to think in terms of the size of the rivers that are going to Be measured it's again something draining around 2000 square kilometers The river discharge is a derived product That does require some fitting you're actually you get multiple versions of the river discharge But what I haven't really highlighted is we don't have all the studies done yet But base flow is probably going to be the best river discharge that we estimate based on the sampling characteristics that we're seeing So good estimates of base flow are pretty likely for these bigger rivers And then as well as the lakes and reservoirs We're going to see the storage change plus have the inflows and outflows of some of the bigger ones It's really going to help close the water budget for these systems Which again can tie back and help understand the groundwater system a little better Just the last plug if anyone's interested in using SWAT synthetic data, let me know we've got a program set up for early adopters