Preservation Photography: Roles and Rules
By Karen Price There’s something about a photograph. Humans are visual and I think pictures…
LiDAR: Pushing the bounds of a technology or using what we have effectively?
The literature surrounding the use of LiDAR, light detection and ranging, imagery can often be disjointed, vague, and impractical for its application in archaeological investigation. Wanting to utilize the available data, I became frustrated with the lack of literature that described a basic methodological approach to using LiDAR. The most common usage for LiDAR in archaeological contexts continues to be identification of sites and associated features. Recent interest in LiDAR’s ability to aid in the monitoring of conditions on archaeological sites offers another opportunity to employ the available datasets (Challis et al. 2008).
LiDAR, light detection and ranging, is the constant transmittal of high-resolution laser light to the ground surface, with the time differential of each pulse recorded at the receiving station attached to a low-altitude aircraft (Fennell 2010:6-7). The accuracy of the method varies dependent on location and how the data was gathered; essentially, a micro-topographic map of the bare surface of the site and surrounding lands can be produced for archaeological analysis. LiDAR has been used in multiple case studies including both prehistoric and historic archaeological surveys with and without vegetation cover (Fennell 2010; Harmon et al. 2006; Petzold et al. 1999).
While the usage of LiDAR in archaeological contexts remains limited, the ways in which it is manipulated and more thoroughly realized continue to expand (Challis et al. 2008; Chase et al. 2011; Devereux et al. 2005; Devereux et al. 2008; Fennell 2010; Harmon et al. 2006; Rowlands and Sarris 2007). The various techniques to extrapolate information include, among others, the application of hill-shading algorithms, the manipulation of illumination sources by direction and elevation, the alteration of contour intervals through arbitrary and relational settings, the creation of local relief models, the application of statistics in analysis to include nearest neighbor, quadrat, and chi-square, the variance of resolution between micro and macro glimpses of the landscape, and even the use of multiple color gradients (Challis et al. 2008; Chase et al. 2011; Devereux et al. 2005; Devereux et al. 2008; Fennell 2010; Harmon et al. 2006; Jaillet 2011; Rowlands and Sarris 2007).
Of course, where there is potential…there is also pitfall. Some of the more common issues with LiDAR that deter it from a more widespread usage include the potential for data overload, inconsistency in its interpretive value, human error or unfamiliarity with LiDAR, present surface imagery’s inability to cope with temporal and/or cultural association, and resolution issues (Harmon et al. 2006; Jaillet 2011). Another point worth noting is that while it is without doubt a useful tool in the archaeological toolbox, it continues to be a method that works best in conjunction with other archaeological methods to include other remote sensing techniques, historic documentation and field investigation (Fennell 2010; Harmon et al. 2006; Jaillet 2011; Kvamme et al. 2006).
At this point, we come to the crux of the matter: what are we doing with LiDAR? In order to get at this question, we could go back to the algorithm. The algorithm most commonly discussed in the literature of LiDAR deals with the language of computers and programming. The meaning, in most instances, is in reference to the computer science behind its analysis and the GIS, geographic information systems, functions used to analyze it. While a great deal has been learned and a great deal more will be learned using this standard definition, I would ask that we apply the most basic ideas behind mathematical induction and recursive relations to our methodological approach to LiDAR analysis.
One solution would be to apply a back-to-the-basics approach involving the basic recursive algorithm of Divide-and-Conquer. Using the Divide and Conquer Algorithm, one would break the larger problem down into two more manageable questions. What can we do with LiDAR, in addition to we have already done? How do we go about doing it, in the most basic sense? It is the second question that appears to be the one plaguing the archaeological community most, as we have excellent examples worldwide of what can be done with LiDAR and archaeologists are continuing to apply it in innovative ways.
We need to come to a consensus on the variables that we are trying to measure using the LiDAR dataset. One way to go about this would be quantification of the variables using archaeological signatures that essentially typify features common to historic and prehistoric site types.
Essential to the idea of the Divide-and-Conquer algorithm is its parallelism, its ability to be used for multiple purposes, just as we know LiDAR can be. The same set of variables can be combined in differing ways to represent the different archaeological signatures expected of different archaeological resources. For example, a historic agricultural settlement might include linear features such as field lines, roadways, and waterways, as well as, polygon features such as structures and specific forms of vegetation. A prehistoric quarry site might include polygon features such as borrow pits and distinctive topographic features advantageous to the process of quarrying for lithic resources. The limits to the use of this technology are as of yet unmapped.
Essentially, what we need is a solution that is both mathematical and manual, a more efficient way to standardize LiDAR analysis. One potential solution would be to compute a coding system to manage the variables and allow for the ability to analyze LiDAR datasets with reference to the individual and combined variables, which would, in turn, limit the number of possible outcomes to a manageable number that could be reviewed and manually analyzed by the archaeologist.
In closing, I ask the archaeological community to rethink the algorithm in LiDAR and continue to expand upon the ways in which we use this valuable tool. Where to from here then… continue to push the bounds of this technology or begin to utilize what we have effectively? Must we make this choice or can we begin to apply consistent methodological standards to our use of LiDAR, while pushing the bounds of possibility?
References Cited
- Challis, Keith and Ziga Kokalj, Mark Kincey, Derek Moscrop, Andy J. Howard
- 2008. “Airborne lidar and historic environment records.” In Antiquity. Vol. 82. 1055-1064.
- Chase, Arlen F. and Diane Z. Chase, John F. Weishampel, Jason B. Drake, Ramesh L. Shrestha, K. Clint Slatton, Jaime J. Awe, William E. Carter
- 2011. “Airborne LiDAR, archaeology and the ancient Maya landscape at Caracol, Belize.” In Journal of Archaeological Science. Vol. 38. 387-398.
- Devereux, B.J. and G.S. Amable, P. Crow
- 2008. “Visualisation of LiDAR terrain models for archaeological feature detection.” In Antiquity. Vol. 82. 470-479.
- Devereux, B.J. and G.S. Amable, P. Crow, A.D. Cliff
- 2005. “The potential of airborne lidar for detection of archaeological features under woodland canopies.” In Antiquity. Vol. 79. 648-660.
- Fennell, Christopher
- 2010. “Archaeological Investigations and LiDAR Aerial Survey in Edgefield, South Carolina.” In African Diaspora Archaeology Network Newsletter. December.
- Harmon, James and Mark Leone, Stephen Prince, Marcia Snyder.
- 2006. “LiDAR for Archaeological Landscape Analysis: A Case Study of Two Eighteenth-Century Maryland Plantation Sites.” In American Antiquity. Vol. 71(4). 649-670.
- Hunter, William A.
- 1960. Forts on the Pennsylvania Frontier (1753-1758). Pennsylvania Historic and Museum Commission.
- Jaillet, Angela S.
- 2011. The People of Pandenarium: The Living Landscape of a Freed African American Settlement.” Masters Thesis. Indiana University of Pennsylvania. Indiana, PA.
- Kvamme, Kenneth L. and Jay K. Johnson, Bryan S. Haley.
- 2006. Multiple Methods Surveys: Case Studies. In Remote Sensing in Archaeology: An Explicitly North American Perspective. Ed. by Jay K. Johnson. 251-268. University of Alabama Press. Tuscaloosa, AL.
- Rowlands, Aled and Apostolos Sarris
- 2007. “Detection of exposed and subsurface archaeological remains using multi-sensor remote sensing.” In Journal of Archaeological Science. Vol. 34. 795-803.
This is a great entry and the references are very much appreciated.
Thank you Bernard! There are a number of resources out there for LiDAR, these are a small sample – but they are a good start for anyone wanting to utilize LiDAR. Other fields are doing incredible things with LiDAR, from the detection of IEDs by US military in combat operations to counting the number and species of trees by foresters, and we can begin to consider some additional possibilities for our own, comparably limited use of LiDAR.
Thank you, Angela, for this useful introduction and great references. Has anyone used LiDAR to search for plowed-over burial grounds/cemeteries? We are planning an investigation of a 40-acre plot in Missouri where we believe there is an historic cemetery, but I am not sure if slight depressions marking grave shafts would still exist after more than one hundred years of agricultural plowing. Any precedents that you are aware of? The area today is simply planted in grass.
Hi Benjamin – You’re welcome and I hope that it does come in handy in your work. I haven’t come across any burial ground/cemetery investigations using LiDAR, but having set that – that does not mean it hasn’t been done. A lot of it would depend upon the quality/scale of your LiDAR data, Pennsylvania has free 2′ contour interval available – which would not be much use if the depressions are slight. Depending on what Missouri has available or what you can obtain, you might be able to do it. It would be worth a try and cheaper than the alternative of Ground-Penetrating Radar if it works… especially if the site is only 40 acres. Best of luck in your endeavors and I’d be really interested in hearing about your results!
Two things: one can we agree use Lidar as the term; just as we do radar. Secondly it is worth alerting your readers to this very good guidance on lidar: http://www.english-heritage.org.uk/publications/light-fantastic/
Bob Bewley (archaeologist)
Hi Bob – You are absolutely right, research questions should be what is guiding our archaeological endeavors. Jonathan hit it on the nose, as you are familiar with the standard methodology behind using aerial photography, I assume you can see the benefit to having a standardized methodology guiding our use of LiDAR. I really love the link you posted above; I also think it calls attention to the fact that European archaeologists have been utilizing LiDAR for some time now. In many ways, they’ve pioneered the use of it and push the boundaries of what we thought was capable for LiDAR. Which leads back to the original question I posted… I don’t think that this is a black-and-white matter. It’s not an either-or question by any means. I do think that we need to be considering the nitty-gritty methodology; otherwise, how can we begin to compare findings? Also, there are a lot of people out there still very much unsure as to how to use LiDAR at all or even appropriately. Thanks for the comments and insight!
Having now read the whole article I am not sure I agree with the question posed. All good archaeological research should start with a question; a reseach question about a place, or time period or a site; then good archaeologists or historians, having aksed the question, decide which are the appropriate techniques and “tools” available to them. Lidar is relatively new – but now at least a decade of work is helping; it is not cheap and as with all ‘remote;y sensed’ data – requires interpretation. It is my contention, having worked in air photo interpretation for many years, that with the right questions and the right – human – interpretation lidar will help answer questions relating to past human land use.
Bob Bewley
I think that we are both in agreement Bob, that Lidar is a powerful tool for archaeologists. Many states in the US have been scanned, some in amazing detail and often that data is available for online use or you can actually download it and manipulate it(
http://www.pasda.psu.edu/ <—has the Lidar data for Pennsylvania). In some states it is actually free, and really useful when planning out a survey.
I could be misunderstanding Angela, but I don't think she is arguing against using research questions, but developing a standardized methodology that could be applied to research questions. When digging a site, you can't just grab a spade and go, you want to do it in a controlled manor. In your experience with air photography, is there an agreed upon methodology for interpreting the data or is it more quantitative?
Jonathan
Hey Angie,
I want to start of saying that I love Lidar, I think the
potential for the
use of Lidar in archaeology is absolutely amazing. Sadly, working in
North Carolina, not many
counties have been scanned, and those that have, are usually not at a level of
detail that would be advantageous to archaeologists. In response to your
question, I think we need to discuss a methodology for the use of Lidar, and
then build on it. An agreed upon methodology
will provide a starting point for researchers to improve.
I’m not sure I understand your argument for variables Angie. Are
you essentially saying that foundations look a specific way when you use X (aka
hillshade, statistics, etc. etc.), sort of creating a typology for
archaeological resources in Lidar? I’ve always looked at Lidar analysis as
qualitative, but are you arguing for a more quantitative approach?
I think what you are doing is amazing and badly needed in the
archaeological community as Lidar becomes more accessible to more researchers. I
think that this space is PERFECT to really discuss a methodological approach to
Lidar, with researchers coming together to talk about it.
Jonathan
Hi Jonathan – I want to thank you for your enthusiastic response to LiDAR! The potential that LiDAR has for archaeological investigation is in many ways still untapped, yet we continue to under-utilize it. As you mentioned, many states have LiDAR accessible and many more are making it accessible. As far as quality and cost, let’s hope that is something that will get better the more the data is used. When USGS topographic maps were first digitized, we experienced similar difficulties and many of these issues have been corrected in recent years. Maybe there’s hope!
As for variables, yes. Creating typologies, flexible ones dependent on research questions and potential archaeological resources, would translate into computer jargon’s algorithms. We basically need to define what we are looking for, what LiDAR is capable of looking for, and what we want to identify as anomalies or features. Many Geographic Information Systems used to process LiDAR data deal with the information in the form of polygons or linear features. So, if you’re looking for an historic farmstead with a well – that’s a polygon feature, whereas the farmlane leading into it would be a linear feature. There’s a wealth of data to process with LiDAR and the most effecient way I see to go about using it would be to determine an algorithm for cultural resources to input into the computer systems to identify “anomalies” or possible features. That’s where we would come back in to the equation – manually determining and field verifying possible features.
Here’s to hoping that clarified things a bit… more questions – ask away!
I saw this on the Subarch List server this morning, anyone else know of underwater/coastal applications of Lidar?
http://www.hydro-international.com/news/id3302-Bathymetric_Survey_of_Bulgarian_Coastline.html
Excellent post. I stumbled upon it a little late. I’m a GIS Analyst working in eastern Pennsylvania and have tried hard to incorporate the PAMAP LiDAR data into our work at Natural Lands Trust. It’s great to see someone else taking advantage of the data. I’ve developed some methods for calculating forest canopy and other forest metrics with the PAMAP data. I just recenlty found the hillshade derived from the LiDAR effective in finding stone fences in forests. I’m always interested in learning more about its use.