Sarah Parcak: Pioneering satellite Egyptology

Sarah Parcak speaks to Chris Smith about her work deploying satellite imagery to the task of finding new sites of interest for archaeologists...

Chris - What's it actually like when you're on a dig in Egypt? It's a pretty harsh environment, isn't it? I mean, it's not only ridiculously hot, but it's like being sandblasted with sand. It's getting into every nook and cranny of your body and you're sweating. It must be pretty horrible. You must have to dig deep, excuse the pun, in order to put up with that day after day. You must really love the subject in order to tolerate that.

Sarah - Yes, it's hot. Yes, there are flies. Yes, there's sand blowing around. But there's something about the pace of a dig and you never know what's going to pop up. You may find a beautiful little bead or part of an inscribed fragment. I've had days or weeks where nothing has appeared, but you're so busy recording all the information, it's fine. I try at least once an hour to pop my head up from wherever I'm working just to look around and just kind of pinch myself. There's still that five- or six-year-old little girl inside you who got that book from the Tooth Fairy. This is your dream and you're living it. You just need to feel grateful and take that gratitude and pour it into the work you're doing.

Chris - So, how did the space element to this come about then? So, you love doing the on-the-ground stuff, getting your trowel into the ground. I thought you were going to say you didn't love it so much and that's why you went after the cool air-conditioned environment of computers and that's how it happened, but clearly not. So, why did you end up looking at satellite pictures?

Sarah - So, you know, getting back to my grandfather, he was famous in the field of forestry because he was one of the pioneers of using aerial photography and aerial photogrammetry for forest mapping and species identification. He's the reason I took my first remote sensing course as an undergraduate and I thought, well gosh, Grampy passed away a couple of years before. Grampy did this. I wonder if anyone has really done this for Egypt or archaeology. Maybe I'll take this course and see. At the time, not many people had applied it to the field of Egyptology.

So, I took that with me into grad school and started developing tools and techniques for archaeological site identification. For me, the best part was I could go and survey and map the sites that I'd found as part of these excavations. So, I was able to do that in the east Delta with my then boyfriend, then fiancé, and obviously now husband. We'd excavate all week and then I'd go off and do survey work on the weekends, and the same at Amarna. I could help with excavations but also go and do survey work on the west banks.

Chris - So, talk us through then how this actually works. What images do you get from space and how do you then use that to find stuff that we didn't know was there already?

Sarah - There are two different kinds of satellite imagery that we use in the field of remote sensing. We're either using what's called passive or active satellite data. So, what do I mean by that? Passive satellites are like Google Earth. A passive satellite is like a camera. It's circling the Earth, taking pictures of what's below and recording information in different parts of the light spectrum — the near, middle, and far infrared, the visual part of the spectrum, and in some instances, microwaves. Then you can take that information and it comes in layers. Each slice is almost like a big sandwich — lettuce, meat, bread. Each slice represents a different part of the light spectrum. Certain features show up or disappear depending on which layer you're viewing. Visual features like houses and roads show up well in the visible spectrum. Vegetation shows up best in the near-infrared due to the chlorophyll. When processing the data, features can appear more clearly due to differences in soil moisture or buried structures.

Active satellite imagery is different — the sensor sends energy down, like radar or LiDAR (Light Detection and Ranging). LiDAR can penetrate forest canopies and reveal what's beneath, creating a digital elevation model. That’s how we’ve revealed tens of thousands of unknown sites in places like the Guatemalan rainforest.

Chris - So, what was your first ‘wow’ moment then? When you thought, right, I'm going to do this for Egypt because it doesn’t look like many people, if anyone, had. You do this, what happened next?

Sarah - I think what really hooked me was during my PhD. I did a big survey project for the first half of my thesis in the east Delta around the site where my husband Greg had been working, a site called Tell el-Balamun, dated to around 2,600 years ago. Using mostly NASA datasets, I looked at the actual chemical signature of archaeological sites.

I thought, we've got all this known site data — what if I inputted this into the satellite imagery, developed tools and techniques, and went from the known to the unknown? That's what we do in archaeology anyway. When I processed the imagery, I had maybe 60 to 70 features pop up that weren’t in any known database. That’s what really kicked me off visiting those sites.

Chris - So, you were actually finding stuff, you were going to places, you began to get results. So, you must have thought, wow, this is really cool. I'm finding new things that people didn’t know were there. That must have been pretty exhilarating.

Sarah - It was super exciting. Not everything was a win. Sometimes I'd go to a site and it would just be a big pile of dirt. Or yes, there was a site, but it was covered by a modern cemetery. I could pick up a little pottery, but there wasn’t much else. For me, the process — the iterative process of science — was also very exciting. Really being critical of what worked and what didn’t. I would then go back, refine things, try new approaches and tools. What's the real method here? Why doesn’t this one work?

For me, yes, it was exciting mapping all these new sites and collecting pottery and conducting settlement pattern studies. But I’m a dorky nerd — the process was, and still is, fascinating. Figuring out how you can put all these tools together at different levels of resolution, both spatial and spectral, to understand what each type of data reveals — or hides.