Mendenhall Program Served as Springboard into Remote Sensing Career for Tollerud

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Dr. Heather Tollerud came to the USGS Earth Resources Observation and Science (EROS) Center with an eye to drought and its ripple effects across time and space.

Which makes sense, given that her doctoral thesis focused on the impact of drought on the dust emissions produced by the dry lakebeds of the Black Rock Playa in northwestern Nevada.

But the Mendenhall Research Fellowship that brought her to South Dakota turned out to be more than an opportunity to use Landsat satellite data to investigate drought. The two-year postdoctoral fellowship became a springboard to a full-time position with the USGS Land Change Monitoring, Assessment, and Projection (LCMAP) program, for which she now leads research and development. The bold new 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.

LCMAP was just getting off the ground when Tollerud arrived. It’s now preparing to release its first collection of data, and is seeking applicants for a new Mendenhall fellow to help the project evolve and improve as it moves forward.

Applications are open through June 3, 2020. Learn more about the fellowship here.

Tollerud recently sat down to talk about what drew her to EROS, and how the Mendenhall program served to further her career in geoscience.

desert floor with mountain in background

Black Rock Desert

Q: Can you tell us what drew you to remote sensing research in the first place. What's your background?

A: Well, 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.

Q: What is a playa?

A: The vocabulary is pretty messy with a playa. There are different parts of the world and different languages that have completely different terminology. But 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. They’re really flat, really dusty, inhospitable places.

Q: And what kind of remote sensing did you use to study playas? What did you use it for?

A: 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 (SAR). 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.

One of the more common uses for that type of data is looking at soil moisture, but we were actually looking at the roughness of the surface. The playa has mineral deposits and evaporite deposits that get sort of crusty and rough. If the surface is really smooth, SAR 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.

Q: You finished your dissertation in 2014. How did you end up applying for a Mendenhall fellowship after that? And what did you pitch? What was your idea?

The (Mendenhall) opportunity was a combination of land cover and land use change, and also environmental factors, in particular drought. So my focus was 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. 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 … in a wet year they will turn very green, and in a dry year, they might senesce (brown) very thoroughly.

Q: You’ve moved on from the fellowship and now work for the Survey. And what are you doing for LCMAP?

Dr. Heather Tollerud with graphic for USGS EROS podcast Eyes on Earth

Dr. Heather Tollerud with graphic for USGS EROS podcast "Eyes on Earth." Hear her episode of the program by following this link.

A: 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. 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.

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

A: I think that I what 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.

Q: What is it that would appeal to a remote sensing researcher with this new LCMAP opportunity?

A: LCMAP is a really exciting project, and it’s using relatively new methodology. There's a wide variety of possible research directions that are just waiting to be investigated. LCMAP is doing this dense timeseries approach, making use of all the data that’s available, and bringing it together into a good format in a way that is really powerful. It can see patterns you wouldn't be able to see if you were just trying to pick one time of the year, because you can see how it changes through the seasons and between the years and across space.

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