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Remote Sensing

Lost Cities, Movie Sets, and Nature's Periodic Cruelty

I have to admit that I was rather excited when I saw the headline "Star Wars home of Anakin Skywalker threatened by dune" in my BBC RSS feed (and not only because, like many Star Wars fans, I'd be happy to forget about Mos Espa along with the rest of The Phantom Menace). The first thing I thought of when I read the headline wasn't the movie, actually, but rather a lecture I saw Michael Moseley give at the Cotsen Institute a few years ago. The talk was mostly about periodic natural disasters in Peru, including sand incursions, and I found it quite fascinating. (If you're interested, he's published on it a number of times, including here, which is conveniently linkable and, unlike many Google Books entries, seems to show the whole chapter.)

This story seems like a neat illustration of that, on a non-catastrophic scale. A movie set is built in the path of a barchan dune, becomes a tourist destination for fans, and less than a decade and a half later people realize that perhaps "in the path of a barchan dune" is not the best place to build something. The slideshow at the top of the BBC piece is nice, although I wondered if Google Earth had more historical imagery. It turns out you can just fly to "Mos Espa" in Google Earth (which really shouldn't have surprised me), but the only image the BBC didn't include is one from 2004. It's pretty cool to be able to go through the 2004, 2008, and 2009 images, though, and see a single vehicle track up the slip face of the dune turn into tracks covering most of the dune until finally, in 2009, the tracks all disappear, covered by sand. It really gives you some perspective on how quickly these dunes can move.

The BBC story is actually a brief summary of an article in press by Lorenz et al. (2013), published in the journal Geomorphology. I have to give the authors props, since it's not every day I get geomorphology stories in my BBC feed. The paper itself, as you might expect for something published in Geomorphology, is primarily concerned with using satellite remote sensing to study the movement of the dunes. There are some interesting observations geared more toward "heritage" and tourism, though. For example, another nearby set building from The Phantom Menace has already been covered by a dune and emerged (seriously, they move really quickly). They note, though, that this caused some fairly significant damage, primarily because the buildings weren't really designed to last a long time or, you know, be covered by a sand dune. This is likely the fate of Mos Espa, too, and the authors suggest that given its potential as a tourism site, something might be done to protect it, like either diverting the dune or just moving the site. This leads them to this great connection:

There would be some irony in such measures being adopted to protect a science fiction film set: it was exposure to eolian transport concerns and countermeasures that inspired author Frank Herbert to write a science fiction novel set on a desert world (‘Dune’) that itself became an epic film. (Lorenz et al. 2013:8)

(Incidentally, beyond its insights on desert cultural ecology, Dune also contains some interesting observations about the uses to which history and archaeology are put, and the processes of remembering and forgetting involved in this. These do get rather heavy-handed by the fourth or fifth installment, though.)

This reminded me of something I actually hadn't thought about in a while: a short literature review I did during my first year of grad school as the initial stage of a cool remote sensing project. That project, for a variety of reasons, never happened, but it did expose me to a neat bit of Hollywood archaeology. The site we were interested in was the so-called "Lost City of Cecil B. DeMille", or the remains of the set built for The Ten Commandments (the 1923 silent film, not the more familiar 1956 Charlton Heston version). The movie was filmed at Guadalupe-Nipomo Dunes near Santa Barbara and, after filming, the sets were taken apart and buried beneath the dunes. This was, evidently, a compromise between hauling them away, which was too expensive, and leaving them intact, which would have allowed someone else to come along and use them. Either way, there they were, more or less forgotten, until they were rediscovered in 1983. Comparing the "Lost City of DeMille" to Mos Espa is interesting, because the underlying problem is basically the same (movie sets just aren't built to last very long), but the environmental issues are different. In the case of the Ten Commandments set, the problem is that the sand is blowing away, leaving the site exposed to damage (more damage than was already caused by taking it apart and burying it under some sand dunes, anyway).

I remembered an archaeological project being in the works at the time I was looking into this (it's mentioned on this site, which doesn't appear to have been updated in a while), and wondered if anything had come of that. Unfortunately, this doesn't look good. I suppose something might have happened after the Dunes Center last updated their web site, but I can't find anything. It sounded like a really cool project, though: digging up the remains of what a legendary filmmaker and his crew in 1923 thought late 2nd millennium BC Egypt would have looked like.

Works Cited

ResearchBlogging.orgLorenz, Ralph D., Nabil Gasmi, Jani Radebaugh, Jason W. Barnes, & Gian G. Ori (2013). Dunes on planet Tatooine: Observation of barchan migration at the Star Wars film set in Tunisia Geomorphology DOI: 10.1016/j.geomorph.2013.06.026

Hyperion in Faynan

Here's another thing that came out while I was in the field, and that I meant to write something about.  A paper by Stephen H. Savage, Thomas E. Levy and myself, titled "Prospects and Problems in the Use of Hyperspectral Imagery for Archaeological Remote Sensing: A Case Study from the Faynan Copper Mining District, Jordan," was published in the Journal of Archaeological Science.  Actually, it's in the Feb. 2012 issue, but through the magic of the publishing process and the internet, this issue is already available.  You can get the article from ScienceDirect here, and Steve has made the preprint available on his web site here.As the title implies, one of the things we tried to do in this paper was describe the things that didn't really work, as well as those that did.  The inclusion of the section on the Principal Component Analysis is a good example.  Some large-scale landscape features were clear, but the false positives and negatives were a bit troubling, and reflect some of the weaknesses of the method and the instrument itself.  One of the biggest problems with using Hyperion for archaeological research is the rather coarse spatial resolution.  Although the spectral resolution is quite good, with 242 narrow bands (for our purposes only 156 were usable), the spatial resolution is only 30 meters.  As a comparison, newer commercial satellites like GeoEye-1 offer resolutions under 2 meters in multispectral bands, and under half a meter panchromatic.  What this means is that some things just don't show up on Hyperion images.  For example, the primary focus of my research, Khirbat Nuqayb al-Asaymir, is a fairly large site (something like 7 hectares -- 70,000 sq.m.), but it's sparse enough that it's basically invisible on the Hyperion images.  This is something of a limitation, and one of the reasons that the focus of this paper is the Iron Age smelting center of Khirbat en-Nahas, which, as you can see if you read the paper, is pretty densely packed with slag mounds.Anyway, I think it's important to publish negative results along with the positive ones, and I'm glad that we did that here.  You can, of course, read the paper and judge for yourself.

2012     Savage, Stephen H., Thomas E. Levy, and Ian W. JonesProspects and problems in the use of hyperspectral imagery for archaeological remote sensing:a case study from the Faynan copper mining district, Jordan. Journal of Archaeological Science39(2):407-420.

Looting and Google Earth

It's been a few days since I started and forgot about this post, so this is somewhat old news, but I'm posting it anyway.I didn't notice when it went up a few days ago, but Heather Pringle has a news story in Science (via) which includes a bit about using Google Earth to map looting activities in Jordan (the parts about mapping Guantanamo Bay are also a good read, of course).I thought this all sounded very familiar, and sure enough, I've had the paper from the Journal of Field Archaeology that she cites (Contreras and Brodie 2010) in my Papers library for a few months now, but hadn't gotten around to reading it. So I read it, and actually it's pretty neat. The authors used data from the DAAHL to identify cemetery sites, and then monitored looting activities using the "Historical Imagery" feature in Google Earth. The idea of using time-series imagery to monitor looting isn't really new in itself, of course. Politis (2002) discussed much the same thing, but using aerial photographs instead, at Ghor as-Safi. Google Earth makes this relatively easy, though, especially because the historical imagery is already there. This is a type of project that's been on my mind recently, so it's nice to see that there's some interest in doing this sort of work.References:

2010     Contreras, Daniel A., and Neil BrodieThe Utility of Publicly-Available Satellite Imagery for Investigating Looting ofArchaeological Sites in Jordan. Journal of Field Archaeology 35(1):101-114.
2002     Politis, Konstantinos D.Dealing with the dealers and tomb robbers: the realities of the archaeologyof the Ghor es-Safi in Jordan. In Illicit Antiquities: The theft of culture and theextinction of archaeology. N. Brodie and K.W. Tubb, eds. Pp. 257-267. NewYork: Routledge.
2010     Pringle, HeatherGoogle Earth Shows Clandestine Worlds. Science 329(5995):1008-1009.DOI: 10.1126/science.329.5995.1008

But is it art?

The Peabody Museum at Harvard has what looks like a pretty cool exhibit running now, called "Spying on the Past: Declassified Satellite Images and Archaeology". Looking only at the Peabody page, the name might seem a bit odd, given that, of the six images they show, at least four are not from spy satellites — nor, to my knowledge, were images from those satellites ever classified to begin with — and one is not from a satellite at all. There's a Boston Globe article from a few days ago that discusses the exhibit, though, and it seems like the focus is heavily on the declassified CORONA imagery. It's an interesting concept for an exhibit, and if I'm in Boston before the exhibit closes (which is a lot less likely than it would have been last year) I'll probably stop by to see it.The line about "modern technology" and its "up-to-the-minute dynamic" in the Globe article struck me as rather funny, though. Those CORONA images are 40 years old now — more than that, even, in some cases.  More importantly, though, the appeal of CORONA imagery for archaeology isn't its up-to-the-minute technology, but almost the opposite: they give us a relatively low-cost, relatively high-resolution view of what these areas looked like 40 years ago.  Although I guess it's still pretty "up-to-the-minute" compared to Tell Brak.

LiDAR in Belize

There's an interesting open-access feature in the latest issue of Archaeology — which also has a nice shot of a tomb at Madain Salih on the cover — about using aerial LiDAR to map features hidden under jungle canopy around Caracol in Belize. ("That's great," I hear you say, "but is there anything in there about the Donner Party's dog?" I'm glad you asked, because yes, there's this.) This story isn't really new — it's appeared in several other places recently — but I read about it then, forgot about it, and then read this as I was glancing at the Archaeology site a few days ago, and thought I'd mention it here.The interesting thing about this for me is that, when I was first told about it by one of the undergraduates (now a former undergraduate) working in our lab, it seemed impossible. The active sensors that tend to be good at "seeing through" things like leaves (or sand) are in the low-frequency, large wavelength part of the spectrum, like L-band SAR (Synthetic Aperture Radar), which has been used to do exactly that. Visible light, on the other hand, is much higher-frequency, and not so good at penetrating dense tree cover. From a common-sense perspective, this shouldn't be terribly surprising; it's darker under dense canopy than it would be if you were standing on top of the trees, because visible light doesn't make it through. So, it seems like what you would get if you took scans of an area of dense canopy would be a very nice image of all of those trees. And this is, in fact, exactly what you get (see the "b" view of this National Geographic image, for example).But somehow they did actually manage to map what was under there, and I think the way it works is pretty neat. As the authors put it:

Initially, the lasers are refracted by the tops of trees, producing a detailed record of the forest cover. But treetops are porous, so some photons penetrate deeper, while others reach all the way to the ground and reflect back from the underlying surface terrain—and any buildings or ancient structures on it. The result is an accurate, three-dimensional map of both the forest canopy and the ground elevation beneath it.
This was my guess as to the only way it could work when I heard about the story last month, and as it turns out, that is the way it works. Again, it makes sense from the common-sense perspective. The only way that an active sensor in the visible spectrum could penetrate forest cover is the same way that light normally penetrates forest cover: through all the little breaks between leaves. After a quick Googling, I fount out that this isn't an entirely new idea, either, although it was the first I've heard about anyone using LiDAR this way. Its application to archaeological survey still seems rather novel, though, and productive for areas where pedestrian survey is made difficult by forest density. And it's always nice to see aerial remote sensing being used successfully to make accurate archaeological maps.References:
2010      Chase, Arlen F., Diane Z. Chase, and John F. WeishampelLasers in the Jungle. Archaeology 63(4). http://www.archaeology.org/1007/etc/caracol.html.

Another lost city found

There's an interesting, albeit quite short, article in the current issue of Science entitled The Map of Altinum, Ancestor of Venice by Andrea Ninfo et al. If you can't access the full text version, you might want to look at the ScienceNOW article -- which is, incidentally, at least as long as the actual article -- to see their figures. As they note, there are no ruins of Altinum; all of that has been robbed out or lost naturally over the years. Their map of the city, then, is based entirely on cropmarks observed in multispectral aerial photographs, and their results are fairly striking.What makes those results striking isn't the spatial resolution of the imagery -- 50 cm multispectral satellite imagery isn't available, but there are several commercial satellites with that kind of resolution in the panchromatic band; even in 2007, when the authors' imagery was obtained, QuickBird approached this kind of resolution -- but the fact that the authors were able to obtain imagery of the area under ideal circumstances. This isn't exactly a new insight -- archaeologists since O.G.S. Crawford have pointed out that the conditions under which aerial photographs are taken can have profound effects on what is visible in the images -- but it's still good to keep in mind. In one sense, this is a good argument for using aerial photography, since it's fairly easy to control when the photographs are taken, but there's also a good argument for satellite imagery in here. If you happened to know that the crops in this area were particularly stressed in July 2007, but didn't manage to get a plane up to take pictures for you, it wouldn't be particularly difficult to find satellite imagery from July 2007.This type of study isn't new, but they've done a really thorough job so far of creating the map of the city. As I mentioned, it's a very short article, but I'm definitely curious to see what will come of this, and how they'll integrate the work they've done so far with the excavations that are presumably to come.References:

2009   Ninfo, Andrea, Alessandro Fontana, Paolo Mozzi, and Francesco Ferrarese.The Map of Altinum, Ancestor of Venice. Science 325(5940):577.DOI: 10.1126/science.1174206