 Hello and welcome to Ask an Archaeologist. I'm Nico Tripsovich and I'm the host of today's show. Ask an Archaeologist is a series of live streamed interviews co-hosted by the Archaeological Research Facility in the Phoebe A. Hearst Museum of Anthropology for Cal Week 2020. Each day at 11 and two, we will interview UC Berkeley archaeologists and answer audience questions. If you have a question to ask, go to slido, sli.do and type in Ask ARF and one word and click on Join and you can type in your question and I'll remind you of this partway through the interview. So today's speaker is Scott Byrom and he's gonna be presenting Dr. Scott Byrom is a research affiliate with the Archaeological Research Facility and he's conducted ground penetrating radar or GPR on Cal projects on four continents. Most of his work is in California and in Oregon. Scott uses GPR to survey sites ranging from shell mounds to adobe ruins and from historic homesteads, cemeteries, fortifications and wreckage sites. Scott will be presenting his talk, how artifacts and ruins before they begin an excavation. So welcome Scott. So my first question is, how do archaeologists use ground penetrating radar to map these things? Well, we'll be able to demonstrate a little more clearly with some imagery, but basically we're using electromagnetic waves to send radar into the ground and then receive a reflection back from the energy that comes back from the objects below the surface and the pattern in those waves, the magnitude and the time of travel is what we use to actually map archeological features below the surface. Do you have slides you wanna share with us? You're welcome to bring those up. Okay. All right, let me pull up a presentation here. Are you able to see my screen yet? Not yet. Okay, let me share this. All right. Let's see, full size there. Okay, so yeah, we can talk about the different techniques that we use when we're using ground penetrating radar and how we identify different types of archeological features. Here I'm mapping a cemetery, actually at Black Diamond Mines and the East Bay. And you can see a GPR profile and a GPR slice map and we'll look at a few more of those. But just to put it in perspective, GPR is different from other techniques that archeologists use to scan the landscape and identify archeological features and characterize entire archeological sites and landscapes. One that's fairly common these days that's very effective is LIDAR. And that's often done, that can be done on the ground with an instrument on a tripod, which ARF uses, but more often it's used from an airplane and can be used, it uses laser technology and light information to characterize topography and features, for example, Mayan cities and channels for agriculture that are present under a forest canopy in the Yucatan Peninsula can be characterized with LIDAR. Magnetometry seen here, held by Niko Tripsovich and his daughter, Sophie and my son, Diego. This is a very effective technique, the gradiometer or magnetometer is great for studying subsurface magnetics. And this technique is useful for identifying especially metal artifacts, but also burn features and bricks and ceramics and things that anything that's got a aligned magnetism to it. But it's a passive technique, it doesn't send a radar wave or it doesn't send any information into the ground, it actually just receives whatever magnetic information is coming in. And then sonar, you can see here on the bottom right is what's used in saltwater. Ground penetrating radar doesn't work in saltwater because the salt crystals attenuate the radar signal, they keep the radar from reflecting back towards the antenna. So with that being ineffective, we're able to use sonar instead to identify shipwrecks that might be on the sea floor, for example. And so that's a very effective technique in saltwater. GPR can be used in freshwater, although it's rarely done so because salt is not an issue in freshwater but ground penetrating radar is the technique that we often use on land. And it provides the greatest detail of any of the techniques for remote sensing below the surface. And especially, it's valuable in that it allows us to look at the depth of different things that we're identifying in contrast with magnetometry, which is two dimensional, it'll only show the magnitude of the magnetic information at a particular location on the site. GPR will show features, but also their depth. So we can look at them in both profile and in plan with slice maps that we make. And here's some GPR in action. This is Professor June Sinseri from Cal who's pulling the 900 megahertz antenna right here with a wheel behind it for measuring distance that goes along the top of the screen as the data's being scrolled across. So there are varied features showing up in an individual transect profile. You can see we're working at a grid that we've marked out with chalk in this parking lot at Santa Clara, Adobe's. And there I am using a three wheel cart with a 400 megahertz slightly larger antenna. Now as the antenna moves across the ground surface, you can see the buried object below becomes more and more visible. And these are different objects right here that are similar to what you see in this diagram over here. So the antenna's moving across up here and then this is the depth scale on the other side in the screen. So that's what we look at as we're doing the GPR. Then as we process it, we get more information. We take that same transect profile and then we can look at multiple transects in a grid and create three dimensional imagery. Basically like a whole bunch of Lego blocks the entire grid would be made of and each Lego block has its own amplitude value. And that allows us to create amplitude slice maps at various depths. And here's a Native American clay house floor feature in California shows up in profile as this sort of darker black and white lines. And then with the color scale that we're using red as high amplitude and yellow is relatively high. And that's the floor of the house that's buried about 60 centimeters down at this site. And out in this area, there aren't any features. Here's a feature closer to the ARF here at Cal at the faculty club. Some, we believe our foundations of cottages that were there before the faculty club was built when this was not actually part of campus but place where people lived off campus in the very early 1900s. And this is what it looks like in profile. And this is where that transect profile crosses the grid, this red line. And so it intersects the feature at various locations, these different foundations. And it's putting together multiple transects profiles that allow us to generate these maps of features below the surface. Are you generally walking in straight lines when you use this instrument? Very important to walk in straight lines and keep them evenly spaced because we're gonna borrow data from adjacent transects. So we need to be able to, if we wobble too much, we're gonna create our own artifacts. We're basically gonna see some errors in the data if we do that. The antenna also have to maintain constant contact with the ground surface. I can't pick it up and go over something and resume unless I make a note of it in my observations notebook that part of the transect will have to be ignored because it won't actually show what's below the surface. So are these different depths? Yeah, so this is a set of different depths. And this is a project that Vallejo's Petaluma Adobe and you're familiar with this one having done the magnetometry work out there. But this is over in Petaluma and it was a massive, it's one of the largest standing historical Adobe structures in North America, I believe. But in the past, there was a southern part of the Adobe. And so our work between Cal and Sonoma State and California State Parks was to characterize the foundation of the Adobe that's no, the portion that's no longer there. And there was one question as to whether or not there was a roof over the Adobe. And I can come back to that a little bit later because we've got some information about that based on our GPR survey. But just to show you how it works, those slice maps that are made up of individual transects processed together in the software that we use, they show us what things look like below the surface at different depths. And again, we're looking at the magnitude of reflections, high amplitude or low amplitude reflections of materials that are down below. And different materials, whether it's an Adobe brick or a stone or just the native soil surrounding have different magnitudes in their reflection based on how quickly they conduct electromagnetic waves. But as we go down in depth, 25 centimeters, 45 centimeters, you can begin to see the rectangular feature. This is 20 meters. So this is 20 yards across, 65 feet across right here. So it's a pretty big area. As you can see in this Google Earth aerial image and those are cars parked down there for scale. You can see this is a pretty big grid. This is a little bit larger coverage than the grids that are in this slice map. This is just partial, but as we get down to 55 centimeters we've got a very distinct rectilinear feature here. What we have are the external walls of the Adobe and then some internal walls for the blocks and then probably some features that were inside the courtyard and inside the structure itself. So this was the planned addition that never got built. So we can expect it to have the similar shape to it was the other half, right? It sure seems to have sort of a reflection. It would have been a square when it was done, I suppose. But we don't know if it ever had. I mean, we know that the foundation was there and that some walls were built but we don't know if it ever had a roof. And that's one of the questions I'll come back to in a minute. Let me just take a moment to remind everyone that if you'd like to ask us questions, if you'd like to send Scott a question here about ground penetrating radar, you can go to the website slido, slido, sli.do and put in ask arf, a-s-k-a-r-f and then you can put a question to Scott either anonymously or you can put your name in and we'll share it with him. Thanks, go on, Scott. So several Cal projects have taken place at California Mission Adobe's or Adobe Era villages. In particular, we've been interested in looking at the structures that are no longer present on the surface. Some of the historical Adobe's like Sanchez Adobe are still standing. In other cases, there were Native American villages that were adjacent that were made from smaller Adobe walls and we're very interested in the history of those places especially. So we've really expanded the methodology for understanding Adobe structures with remote sensing. In a lot of cases, archeologists have had difficulty identifying them, but our techniques are showing pretty clearly the foundations of Adobe's at several sites. In some cases, we're looking at the sandstone blocks themselves, the San Juan Batista, and even in 1856, it was a ruin that was collapsing. There wasn't much left of this from this native family housing that was built in around 1820, I believe. Our affiliate, Glenn Ferris, took the lead on this project and we did the GPR there in 2015, I believe. And here's where the transect crosses the Adobe wall and outside of the wall, we believe are a series of the posts that were put in to support the roof because the roof has to extend beyond the Adobe's. And this is what the site looks like today. There's no evidence of the Adobe on the surface, but you can see it in the GPR data. Now, if we go back to the Sanchez Adobe, you can see those posts and the extending roof that overhangs. And to go back to the Vallejo Adobe, that was one of the questions they had for us in starting this project was if there was any evidence of the roof having extended beyond the wall and we don't see those in the grid at Vallejo Adobe. So we can conclude that they probably didn't ever complete that part of the building. Just a couple of other examples of places where we've done work on Adobe's. I wanted to ask on the previous slide, it looks like you have a historic map lined up. Are you able to use these historic maps to help locate old walls? Often we do, yeah, we have some information, but again, with the Mission Adobe's, we have the best information about the most well-known structures. And we don't typically know that much about, for example, the Native American villages that were adjacent to the Mission Compounds. So sometimes we're going with known maps. In this case, these were commissioned by the Mission itself to be built. So we do have some records, but Glenn was able to draw up this diagram based on his archival research and then an archeological test trench and some probing with the rod that determined where some of the stones were. And we confirmed its characteristics with the TPR and then we were able to locate the, identify the posts outside the structure as well. We have a viewer question here. They wanna know if you can find burials or skeletons with this technology? It really depends on the situation. I would say in many cases, historical cemeteries from the last couple of hundred years were able to see where the graves are located, especially the grave pits. If the coffin was very substantial and certainly if there's any metal involved in its construction, we'll be able to see that typically. Often we just see the pit itself and we don't see the contents too clearly, especially if it's, it would just be bones and deteriorated clothing and the pine box or something. But so bones don't typically show up very well, but the pit itself does. And if there's an excavation that needs to happen at that location, the archeologist typically follows with the probing to determine what's in the pit after I've determined where the pit is with the GPR. So we can confirm them. It looks like you're showing us a profile showing a void. So this is perhaps what these pits look like. Yeah, actually, if there were a coffin with the intact top, then it would look a little bit like this does right here with the void underneath. This is a void at a cavern location just to show how we can locate tunnels and culverts. So this would have had a reinforced roof on it which may provide more reflection as well, right? Yeah, you can see the stonework that's in an archway here. That's pretty typical in some of these older catacomb type features. Another setting where we've done several cal projects. Dr. Kent Lightfoot has led extensive research at Fort Ross and we've done several GPR projects since 2012 out there. This is probably the remains of the flagpole pit in the center of the stockade. We identified as one example, it's another GPR profile. Yeah, Professor Lightfoot will be speaking with us later this week, I think. Wonderful. Thursday or Friday. What did you find there? You were looking for a flagpole, you said? Yeah, actually, Glenn Ferris, who's formerly the head archeologist for California State Parks and now an ARF affiliate, was interested in locating the historic flagpole location that would have been put in around 1817. And he, based on sketches and his assessment of the archival materials, he thought it was within this area. He made a small grid about four by four meters. And so within the center of the stockade, actually it wasn't exactly in the center, it was offset a bit, but so we ran a series of transects within that small grid and we found a pit just about where he had put his wooden stake where he estimated it to be. There hasn't been any subsequent excavation but I think eventually there's a plan to test that and see if that's actually what it is. In other cases, we looked at the Russian cemetery from where the officers and traders were buried and identified graves that weren't previously known about for preservation. That's just for monumenting purposes. Our next project involves looking at the village that was outside the stockade where Russians were intermarried with Pomo native women and there was a village there outside to the west or northwest of the stockade. Unfortunately, from my perspective, there was a ranch that was built on top of it, the call ranch. So I'll have to be differentiating ranching arrow features from the village but that's also what the archeologists on the project, the other archeologists will be focusing on through their excavation, they're able to do those. So is GPR, is there interference from other things in the area like, I know that magnetometry, you have to be very careful about the presence of ferrous objects, old plows, nails. Seems like GPR is more tolerant of noise. Yeah, it does pretty well around metal. Let's see, if I'm going up against the metal chain link fence or sheet metal, if that's nearby, I can get some reflections off of that but I could generally still get good data. The only problem is if I'm having to go over metal, I won't be able to get much radar data through it. And actually within Fort Ross, State Parks has put down a mesh grid to protect, to keep their paths from being dug up by rodents, by gophers, for example. And I don't get any data when I go over those pathways. Elsewhere I can go over concrete or asphalt and get really good data through that as long as there's not too much rebar in the concrete. But yeah, metal mesh and sheet metal, things like that really just prevent me from seeing just straight through it, but I'm not usually affected by a nearby metal. I see. And I know you've used this in beach settings to find things buried in the sand. Are there issues with being near the ocean? There are. You can get quite a bit of information from the upper portion of the beach. Sand is actually an ideal situation for doing GPR. But once you get into an area where there's saltwater intrusion, which is gonna happen before you start to see the moisture on the surface or where the waves are hitting, then the salt keeps the radar from being informative because the salt crystals are basically sending the radar energy away from the instrument, not reflecting it back. We call that attenuation. Well, let me take a moment to remind everyone that if you wanna send us questions, you can go to sli.do and type in ask arf and you can write questions to Scott. We have about five or six more minutes. So there's still time to field some questions. We have one that just came in from Slido. They wanna know, similar to what I was just asking, are there side effects or downsides or limitations to this technology? I know that you need to contact the ground really well, right? So maybe vegetation is an issue. Yeah, those are the sorts of limitations. You want a relatively smooth ground surface. This site that we're looking at here, the curb is a little bit of an issue as far as running transects across it. And then of course, this eroding path, it's a recreation area on the coast, but there's a shell metal layer and you can see how well the layers show up down below. Getting across the curb becomes a little bit of a, if I go up and over a curb, then it's gonna show, the radar data is gonna show an artificial pit because I'm basically going up and away from what's below and then coming back down to it. So a nice smooth surface, you're not always gonna get that at every archeological site, especially in an area big enough to do a grid. So we're often confined in where we can set up our grids based on that. But there aren't any side effects in terms of, people sometimes ask about radiation. It's radar energy, it's electromagnetic energy, so it's radio waves basically. It's basically like cell phone energy, for example. So I assume you have to go around objects like poison oak bushes, trees, and so you'll have a divergence from your grid and then you have to kind of deal with that in the interpretation stage. Yeah, and if we can use in situations where we can use high precision GPS, RTK, GPS in real time, then the data can, we can have a gap in the middle of the grid and it's not a big deal. But for the processing, it's best to have the entire rectangle filled with adjacent transects. So I definitely spend a certain order. In order to make that slice cut. Yeah, this is where my teenage sons are helpful for doing some clearance, brush clearance before we're actually out there gathering data. We're often out there with our gardening tools, smoothing things off just to make it just the right. So we get the best data at a time. And how did you get into this technology? Was it difficult to get the background and learn it? You need to know a lot about geology or soils to properly use this instrument? Yeah, I think it was really helpful that coming into this, I started doing GPR, well, 2005 was my first project, but I didn't really do it in earnest until as my main focus within archeology until about 10 years ago. But prior to that, I'd had extensive experience on excavations. And I was really familiar with excavating sites in a lot of different environments in California and Oregon. And that's really helpful that information. I mean, I can't really envision going straight into doing GPR and archeology without having a fair amount of experience at different types of archeological sites. Geo archeology is a really great focus to have to understand the GPR data. Yeah, I think understanding stratigraphy, different types of soils and their properties. And of course, then understanding the variation in archeological features, what a privy feature or the pit underneath an outhouse looks like a hundred years after it's been buried. That's something that you know from excavation, typically, and translating that into assessment of a GPR profile feature takes a fair amount of that experience. And we have a question. Somebody wants to know about the most exciting discovery you've made with this technology. Wow, there have been a lot of great ones, I think, but one site that I found with GPR that I think is pretty special, it's in the, we wrote it up in the archeological research facility series in the book, Triangulating Archeological Landscapes. Camp Castaway is the name of the site. It's on the Oregon coast, actually in the dunes, not in this setting, but in a real wide open dune area. It was a camp that was formed in 1852 when soldiers from Benesha down here were on their way to Port Orford in Oregon and they got caught in a storm and their ship wrecked on the beach in Oregon. And they formed a military camp for four months and they traded with the Coost Tribe locally and were able to sustain themselves through those months until the end of winter and they salvaged the cargo of the ship and then finally were able to take it down to Port Orford, which was about 50 miles to the south. And I was able to use GPR to relocate that camp which people had thought had been washed to sea 100 years ago. It hadn't been seen in over 100, almost 150 years, but the radar showed me buried iron rods and things. And of course, in that case, I used archival maps, historic maps were really key in going back and relocating that. Luckily the US Coast Survey had done some fantastic mapping of that coastline, just like they have around San Francisco Bay back in the 1850s. Oh, that sounds like an exciting find. And I guess you didn't run into the problem of saltwater there because you were high enough on the dunes. That's right. Although I did do some transects down towards the beach looking for the actual shipwreck itself. Often the ships have ballast in them that we might be able to identify but if that's in the intertidal zone, then I'm probably not gonna see it because of the saltwater. And I didn't see any evidence of the ship itself. Most of the ship was taken apart though to use for building that camp. Mm-hmm. All right, well, that's about all the time we have. So I wanted to thank you, Scott, for joining us on Ask an Archaeologist. And I wanna thank the listeners and the viewers who sent in questions. And I'd like to invite listeners to our next Ask an Archaeologist. I'll be speaking with Professor Kim Shelton from the Classics Department this afternoon at 2 p.m. She's presenting on the topic of digging up the heroes of ancient Greece. So please join us at 2 p.m. Thanks again, Scott. It was great talking with you. Thanks. Go Bears.