Eyes on Earth Episode 22 – Meet the Mendenhall Fellow

HULT:

Hello everyone, welcome to this episode of Eyes on Earth. We are a podcast that focuses on our ever-changing planet and on the people here at EROS and across the world who use remote sensing to monitor and study the well-being of earth.

Today, weíre going to spend some time talking about a research opportunity thatís available now through the U.S. Geological Surveyís Mendenhall program. The program offers a variety of post-doctoral fellowships across the Survey, including one at EROS.

Dr. Heather Tollerud took advantage of the Mendenhall program after earning her Ph.D from Pennsylvania State University, where she used remote sensing data to investigate the pockmarked surfaces of dry desert lakebeds, and to model the interactions between drought and dust emissions on those harsh landscapes.

Heather came to EROS through the Mendenhall program in 2015. She now leads research and development for Land Change Monitoring, Assessment, and Projections, also known as LCMAP. This bold new USGS initiative uses every available pixel of Landsat satellite imagery to map more than three decades of land cover change, year after year, for every 30-meter plot of ground in the nation.

EROS is currently looking for a Mendenhall fellow to work with Heather and her colleagues in this exciting remote sensing program.

Heather, welcome to Eyes on Earth

JOHN HULT:

Heather, why donít you tell us what drew you to remote sensing research in the first place. What's your background? 

HEATHER TOLLERUD:

Well, so my undergraduate degree is in math and science and then I went to graduate school in astronomy. That didn't quite work out for me, so thinking about what to do next, I decided to switch and do geoscience. My dissertation work focused on remote sensing and dry playas and dust emissions.

HULT:

When you say a playa, can you explain what that means for some people might not, might not know what a playa is. What's a playa? ë

TOLLERUD:

Yeah, the vocabulary is pretty messy with a playa. There are different parts of the world and different languages have completely different terminology. But basically, a dry lakebed is one way to put it in English. Out in the western U.S., there are a bunch of areas that were lakes during the ice ages, and that now are dry. And so theyíre these really flat, really dusty, inhospitable places. 

HULT:

I see. And you were studying playas using remote sensing then, after your initial degrees?

TOLLERUD:

Yes, that's correct. 

HULT:

And what kind of remote sensing did you use there? What did you use it for?

TOLLERUD:

Well, so first of all, we were looking at some hyperspectral data from Hyperion, which is actually from EROS. The other data source was synthetic aperture radar. We used that to look at the surface roughness of the playa to try to better understand how it evolved after flooding events during the wintertime. 

HULT:

And when you say synthetic aperture radar data, what does that tell you?

TOLLERUD:

One of the more common uses for that type of data is for looking at soil moisture, but we were actually looking at the roughness of the surface. So the playa has mineral deposits and evaporite deposits that get sort of crusty and rough. If the surface is really smooth, it sends a signal down and it just bounces off away from the satellite and you get a really low return rate. If it's a rough surface, some of the signal bounces off some rough areas and comes back to the satellite. So rough areas are bright. 

HULT: 

Got you. So that's how you were able to tease out those details. That's how the sensor was able to tease out those details, in other words. 

TOLLERUD:

Yeah, yup.

HULT:

And where did you perform this research? You were in the western United States, but where did you study? Where was this? 

TOLLERUD:

The study site that I was looking at was the Black Rock Desert, and some other areas, too, but especially the Black Rock Desert, which is northwestern Nevada. 

HULT:

So that was the topic of your dissertation, and you finished that around when, then?  

TOLLERUD:

Um, whatís that, so Ö 2014, I guess.

HULT:

So 2014 came, you finished your dissertation, you got the Ph.D, and then you said ìwhat am I going to do with myself?î And then the Mendenhall just sort of fell in your lap or what? How did you end up applying for a Mendenhall fellowship? And what did you pitch? What was your idea? 

TOLLERUD:

I was looking around for a postdoc offers. And so since I was in a geoscience program, it made a lot of sense to look at the Mendenhall posting. I saw that there was one out at the EROS Center that looked like it was a pretty good match for my background. I knew that Mendenhall program was a good program, so I figured I would give it a try. 

HULT:

Was there a particular focus for this Mendenhall application? Was there something that you were looking at?

TOLLERUD:

The opportunity that I saw on the website was a combination of land cover and land use change, and also environmental factors, in particular drought. So my focus then was on the impact of drought on different types of land cover, and what impacts drought might have on interactions between climate and the land surface. Some of the research results where that grasslands tend to see the widest results, which is really relevant for this part of the country. 

HULT:

You say grassland had the widest results. What do you mean, what are you getting at there?

TOLLERUD:

Croplands don't necessarily change as much, especially during some parts of the year, because more or less the same thing happens. The farmers go out and plant the crops in the spring and so forth. Whereas the grasslands Ö in a wet year they will turn very green, and in a dry year, they might senesce very thoroughly. So the way they look in the satellite images are very different. 

HULT:

So you can see a lot more of the dynamics, the interaction between climate and the land on grasslands than you would in, you know, say, a cropped, in croplands.

TOLLERUD: 

And certainly there's a lot of impact and other land cover types too, but it's just that in grassland It's particularly strong, and it's also particularly consistent. If you have a sort of similar drought forcing, you tend to see a fairly similar response, whereas in something thatís more managed, maybe you have a bit more variation in the response.

HULT:

Right, right. So how did you move from that into Ö Well, let's step back a second. So right now with LCMAP, you have moved on from the fellowship and you now work for the Survey. And what are you doing for LCMAP?

TOLLERUD:

I'm heading up the research and development team. We are focused on improving the LCMAP analysis methodology right now. We've been looking at how to extend LCMAP forward, and then also what kind of modifications we might see when we go to Landsat Collection 2 from our current input data of Landsat Collection 1 

HULT:

So you started out looking at the impact of droughts on these various land cover types, and now you're in a position where you're working for a wide-scale land cover mapping, and you're looking at how to extend that project into the future? Because right now you're looking at the past, right? Like LCMAP maps what's on the land surface from like 1985 to 2017, right? 

TOLLERUD:

So we're looking at developing methodology for continually keeping the LCMAP results updated. And the approach intrinsically was conceived of as something that would move forward in time. It's very tractable, but there are some details that needed to be worked out before we could get it to actually happen in the real world.

HULT:

Right. And you're basically a part of the team that's helping to make that real world part of LCMAP happen, where you're continually tracking year after year and adapting as Landsat adapts to things like Collection 2, like you mentioned Ö you're part of the team working to make that happen right now.

TOLLERUD:

Yeah, and improving the methodology and hopefully improving the products and that data access, as well. 

HULT:

Do you think, Heather, that you would be doing that kind of work were it not for this Mendenhall Fellowship?

TOLLERUD:

I think that I ended up doing was going to be very influenced by what I ended up doing for the Mendenhall. I don't see an obvious pathway between the two without the Mendenhall program.

HULT:

Right, so basically you started out at EROS with this specific focus, and because of what you learned there, you're now in a position where you're leading one part of a major project?

TOLLERUD:

Yeah, thatís Ö mm-hmm. 

HULT:

What is it that would appeal to a remote sensing researcher for this opportunity in particular? 

TOLLERUD:

Yeah, well, so LCMAP is a really exciting project, looking at land change. And itís using relatively new methodology, and there's a wide variety of possible research directions that could be looked at that are just waiting to be investigated.

HULT:

Can you speak to some of that? Can you speak to some of the opportunities, some of the things that a person might be able to do with LCMAP data or be able to do using this methodology that might be exciting?

TOLLERUD:

In my area of interest, in drought, thereís the potential to make use of some of the LCMAP data to look for deviations from what the model might expect, and to try to interpret that as differences in vegetation and impacts of drought.

HULT:

So youíre talking about deviations Ö so like when a drought happens, we expect this, that, and the other thing. If I'm reading between the lines here, I think what I'm hearing you say is you're able to see, because of the depth of the data and because of looking year after year, you're able to see some of the things that you wouldn't expect?

TOLLERUD:

Yeah, yeah. Well, and I guess that helps highlight another thing that's really interesting and powerful about that sort of approach LCMAP is doing which is this dense timeseries approach, and making use of all the data thatís available that we can bring together into a good format is really powerful. It can see patterns that you wouldn't be able to see if you were just trying to pick one time of the year and whatís happening then, because you can see how I change through the seasons and between the years and across space. So this sort of large dataset, dense timeseries approach is really powerful. 

HULT:

Gotcha, gotcha. And again, your area of interest was drought, but if someone were interested in say, wetlands, or fire and recovery, changes to coastal areas, there are a lot of things that you could look at using this approach?

TOLLERUD:

Anything that's pretty reasonably looked at at 30 meters. And actually even potentially smaller than that in shorter time periods. 

HULT:

Anything you can see in a plot of land thatís 30 meters square. You put a bunch of those pixels together, if you can see it, then it can be studied with LCMAP over time. 

TOLLERUD:

Yep. Yep

HULT: 

Heather, thank you for joining us for this episode of Eyes on Earth.

TOLLERUD:

No, thank you for having me. It was a pleasure. 

HULT:

Thank you for listening to this Eyes on Earth podcast extra. Be sure to join us next time for more conversations on Earth observation, satellites, and much, much more.

This podcast is a product of the U.S. Geological Survey, Department of Interior.