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Nebraska Anthropologist Anthropology, Department of

1999

Geophysical Survey as a Conservation Tool

Anne M. Kern

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Kern, Anne M., "Geophysical Survey as a Conservation Tool" (1999). Nebraska Anthropologist. 118. https://digitalcommons.unl.edu/nebanthro/118

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AnneM. Kern

With the introduction of cultural resource management and the passage offederal preservation legislation more than thirty years ago, American archeology has recognized the need for non­ invasive practices that produce significant, new data while preserving the non-renewable archeological record. In the early I 970s, Thomas Lyons and the National Park Service's Cultural Resource Management Program began to develop a non-invasive paradigm placing new emphasis on remote sensing techniques. Developments in geophysical methods over the past twenty to thirty years allow archeologists to preserve the archeological record, practice Lyons' non-invasive archeology, and collect high-quality data. A discussion of the advantages and disadvantages of geophysical applications follmvs.

"As archeologists are becoming more concerned with cultural resource management, non-destructive techniques such as geophysical surveys are becoming more valuable tools. The shifting focus in American archeology tmvards management and protection of the nonrenewable archeological record has resulted in less destruction of non-threatened sites through excavation. William Lipe, in his 1974 article "A Conservation Model, " stressed this vel}' need" (Lipe 1974).

For decades the National Park Service years of experiments with sites such as has been the main federal agency charged Chaco Canyon, Lyons and his office literally with the protection, conservation, and wrote the book on how remote sensing was management of the nation's cultural to be incorporated into cultural resource resources. All federal agencies were so management (Lyons and Avery 1977). charged as a result of legislation in the Lyons advocated a new methodological 1960s and 1970s. It is no surprise, then, that approach for "exploration, discovery, the National Park Service has been at the recording, evaluation, investigation, forefront of promoting the use of non­ monitoring, and management of cultural invasive archeological techniques. For resources" (Lyons and Scovill 1978:3). thirty years it has been refining the Rather than use the imprecise methods of applications of remote sensing and surface survey and subsurface testing, these geophysical methods to study archeological methods should be reserved for site sites with minimal impact. verification instead of site discovery. He points to the flaws in the traditional methods Non-destructive Archeology in the following scene:

Thomas Lyons and the National Park Frequently archeologists still Service's Cultural Resource Management in training and with varying degrees Program began studying the applicability of of professional accomplishment and remote sensing to archeology as early as observational prowess walk the 1969 (Lyons and Scovill 1978). Based upon ground Oil site surveys. They

74 visually search for, discover and subsurface complement to the remotely concurrently assess, sift and select a sensed surface data. highly limited number of physical attributes deemed to be adequately Lyons recognized the vital importance descriptive and representative of of remote sensing and geophysical rather obvious classes of techniques for developing a non-destructive archeological and natural archeology. The application of a non­ phenomena. They record mentally destructive archeology is, in tum, vital for massaged observations of these judicious administration and management of physical phenomena in summary cultural resources. Volumes of information fashion in logs, diaries and on about a site can be obtained without invasive printed forms, using imprecise excavation. Multiple surveys can be terminology and syntax in an often conducted while saving the site for future undecipherable scrawl. They plot study and the development of new site locations with Brunton compass technologies. accuracy, a technique that often precludes rediscovery and positive Non-destructive Techniques identification of them at a future date. From this process comes a Several terms have been developed to highly personalized statement about refer to the variety of non-destructive the archeology of an area and the techniques now in use. As noted earlier, the natural environment, a statement remote sensing techniques Lyons began that invariably concludes more experimenting with were of a different surveying, more collecting and more nature than those in use today. Remote excavating of the resources are sensing methods, as they differ from required (Lyons and Scovill geophysical applications, refer to data 1978:4). obtained from a remote platform, such as an airplane, satellite or otherwise elevated His complaints extend to include the instrument. Aerial photography, infrared on-the-spot interpretation involved in and other measurable light in the surface collecting, the inability to replicate electromagnetic spectrum are data types the initial observations once a surface survey obtained in remote sensing (Lyons and is done, the limited nature of the data Avery 1977, Heimmer and DeVore 1995). collected from survey and testing, and the limits of human senses. This dissatisfaction Geophysical prospection implies created a paradigm he termed non­ looking beneath the surface rather than on destructive archeology, which utilized top of it. This is the broadest, most remotely sensed data to explore, discover, inclusive term for all geophysical and record sites. measurements taken to determine the subsurface composition. It includes both Twenty-five to thirty years ago, the non-destructive methods as well as primary tools in remote sensing available to minimally invasive techniques such as Lyons were aerial photography, satellite coring or drilling. The term is used more imagery, infrared data, and photogrammetry often in British than American archeology (Lyons and Scovill 1978). Over the last (Rapp and Hill 1998). decade or two, geophysical techniques have advanced greatly and their applicability has Non-invasive geophysical techniques been tested in archeological settings. fall into two categories, passive and active. Borrowed from geophysics, these techniques Passive methods involve instrumentation measure various physical properties of the that can precisely measure physical subsurface make-up. They provide a properties of the subsurface such as

75 magnetism and gravity. The passive method stressed the objectivity in data collecting most commonly used is some form of a with a geophysical instrument as opposed to magnetic survey. Two magnetic human detection (Lyons and Scovi11 1978). measurements are usually taken for every In sheer quantities, the amount of data point in the survey and the differences or obtained using geophysical instruments wi11 gradients are calculated in order to eliminate be exponentially greater than the amount of natural daily variations in the earth's data amassed after traditional surveying and magnetism. testing.

Active techniques involve inducing an The nature of that data is also electric or magnetic field through the important. Geophysical data in digital form introduction of a current. The introductions are easy to store and retrieve. Traditional of acoustic and radar waves are also methods can produce cubic feet of artifacts considered active geophysical methods. and volumes of field notes that require Examples of these methods include: storage in already crowded curation electrical resistivity, electromagnetic facilities (Lynott 1997). Improper storage conductivity, and ground penetrating radar has the potential to damage or destroy (Heimmer and DeVore 1995). artifacts. Once an assemblage has been curated, rarely does it ever re-emerge for Geophysical Advantages further study. Whole collections have been known to disappear into a "curational As stated, the greatest advantage in abyss." Digital data have a greater potential the use of geophysical techniques is their for re-evaluation. The quality of digital data non-destructive nature. To cultural resource is not likely to diminish over the course of managers, this is an attractive quality. They time. Geophysical data are also very are able to obtain usable subsurface data precise. Depending upon the sampling while remaining true to the preservation and strategy, a traditional survey will predict the conservation ethic. By not destroying the location of a fraction of the sites in a given archeological record, the site is preserved area. Geophysical surveys can identify for future study when new technologies every potentially human-made anomaly in become available. Geophysics can give the the same area. Human alterations to the dwindling archeological record extended life landscape, such as ancient roads, trails, and maximize the amount of information agricultural fields or other features without obtainable. an artifactual reflection that could not have previously been identified can be In Great Britain, where archeological represented in the geophysical data. resources are even more limited in its volume, geophysical techniques have been Thirdly, the cost-effectiveness of incorporated into research for decades using geophysical -methods over traditional (Coles 1972). Not only can geophysical excavation is not directly measurable in techniques aid in site discovery, but also dollars and cents. Intangible factors are allow British archeologists to maximize site difficult to insert into a fiscal equation. information before excavation. The Costs are also very situational which make successful use of these techniques in Britain comparison between projects difficult. slowly helped to convince American Cost-effectiveness can, although, be archeologists of their utility. measured in broad terms. Generally speaking, geophysical surveys can be The second advantage to geophysical conducted with fewer crew members. Most applications is the quantity and quality of of the geophysical methods are very quick, data obtained as contrasted with traditional decreasing the time needed in the field. No site discovery techniques. Again, Lyons lab facilities are required to pre-process the

76 data prior to analysis. As stated above, the "Remote sensing is not a panacea" (Lyons digital format is much less costly than and Scovill 1978). Each geophysical curational fees and needs. Although the method has specific limitations and technology is itself expensive, after the conditions under which it can and cannot initial capital outlay to purchase the work. Equipment limitations to be instruments, little additional costs are considered include power source. The necessary to acquire additional data. Every instrument lasts only as long as the battery, few years updated software or spare parts unlike manual labor, which can be might need to be purchased. The largest replenished with a short lunch break. The intangible to consider is that of not properties measured in each method are destroying the site. How does a cultural suited to detect particular types of resource manager measure this benefit? anomalies. Geophysical surveys must be However it is measured, it is certainly great. evaluated on two conditions-the environmental conditions and the type of Geophysical surveys have the ability anomaly it detects-to determine the to make subsurface testing itself more cost­ methods most applicable to the specific effective. Anomalies found in geophysical project. Adequate pre-field research about surveys can be targeted for testing when the instrument's limitations, the site's time and cost constraints exist (Lynott geomorphology, and the probable 1997). Projects that do not involve archeological features of the area to be threatened sites, but lack funds to surveyed must be done in order to properly accomplish very much, may choose to apply geophysical techniques. conduct a geophysical survey to obtain the maximum amount of data for their money. Geophysical survey also requires a When more funds become available at a trained analyst to interpret the data once it is later time, the research can then be guided collected. This person can usually be found by the geophysical findings. in a geophysicist or someone adequately trained in geology or physics. The Because public tax dollars fund the specialized analyst will likely add to the cost majority of archeological projects of the survey. Without such a person the conducted, agencies and researchers have a interpretation of the geophysical data takes responsibility to the taxpayer to use the longer. Although geophysical surveys are funds efficiently (Lyons and Scovill 1978). able to detect nearly every anomaly, the data When no surface clues exist to suggest the are still interpretive. A great deal of gray presence of an archeological feature, area exists in which the analyst cannot be geophysical surveys can look beneath the conclusive about the cause of the anomaly. surface. These methods have the ability to As with traditional data interpretation, the locate sites and features where archeologists issue of equifinality appears. More than one may not commonly look. cause may explain a particular anomaly.

Finally, geophysical techniques may Ground Truthing provide an alternative in sensitive situations such as those involving sacred sites, Although geophysical techniques are cemeteries, and possible human burials. regarded as non-invasive, they require Even then, geophysical techniques may be verification that can only be accomplished objectionable, but they offer a non-invasive through subsurface testing methods. In solution (Lynott 1997). Lyons' non-destructive archeology, he clearly states the necessity of testing as a Geophysical Limitations means to verify the remotely gathered data Although geophysical surveys have (Lyons and Scovill 1978). Ground truth, the numerous advantages, limitations exist. verification step Lyons refers to, is key to

77 the further development and refinement of data produced can provide a comprehensive geophysical methods. Knowing what view of the project area and all potential anomalies the instruments detect and what features located within it. Geophysical data they cannot detect helps in the interpretation are easy to store and retrieve while of the geophysical data in the subsequent geophysical techniques provide the ability to surveys (Lynott 1997). conduct multiple surveys. These surveys are relatively cost-effective once the equipment Summary is initially acquired.

Having examined the numerous The applications of geophysical benefits of geophysical applications in techniques in archeology are readily cultural resource management, why would apparent when considering situations any archeologist choose to begin blind? involving sacred sites or cemeteries. They Despite efforts by Thomas Lyons, the use of can provide a snapshot beneath the surface remote sensing for a non-destructive when no evidence for a site exists on the archeology has not replaced traditional surface. The most obvious application methods for site discovery and exploration. involves geophysical data providing Archaeologists are a stubborn breed and guidelines for subsurface testing. Not only Lyons could not dissuade them from does this increase the efficiency of the conducting surface survey and shovel tests testing phase, but it also provides feedback as means for detecting sites. To this day the in furthering refining the use of these shovel remains the tool preferred over the techniques in archeology. Geophysical cesium-vapor magnetometer when locating surveys are not uniformly applicable to all sites. To his credit, Lyons' non-destructive projects. Knowledge of the instruments' paradigm has made an impact within many limitations and the site's geophysical of the federal agencies charged with cultural properties will enable archeologists and resource management. University resource managers to better apply this researchers are applying this technology to a technology in each specific circumstance. lesser degree with private archeology firms falling somewhere in between. Overall, geophysical applications are precisely the type of non-destructive The use of geophysical surveys offers techniques Lyons champions in order to numerous advantages over traditional survey better conserve and protect the archeological methods, the greatest of which is its non­ record. As American archeology enters the invasive quality. Volumes of information next century careful management of can be gleaned without breaking ground. archeological resources will become more The instrumentation can remove a great deal critical and geophysical surveys will become of the observation and collection bias. The the norm as Lyons envisioned.

References Cited

Coles, J. 1972 Field Archeology in Britain. Methuen & Co, London. Heimmer, D. and S. DeVore 1995 Near-Surface, High Resolution Geophysical Methods for Cultural Resource Management and Archeological Investigations. Revised Edition. Interagency Archeological Services. National Park Service, Denver, Colorado. Lipe. W. 1974 A Conservation Model for American Archeology. The Kim 39:213-245.

78 Lynott, M. 1997 Geophysical Surveys at Two Earthen Mound Sites, Wright-Patterson Air Force Base, Ohio. Midwest Archeological Center, Lincoln, Nebraska. Lyons, T. and T. Avery 1977 Remote Sensing: A Handbookfor Archeologists and Cultural Resource Managers. National Park Service, Washington, D.C. Lyons, T. and D. Scovill 1978 Non-destructive Archeology and Remote Sensing: A Conceptual and Methodological Stance. In Remote Sensing and Non-Destructive Archeology, edited by T. Lyons and J. Ebert. Publicaiton No. 36. Remote Sensing Division, Southwest Cultural Resources Center, National Park Service, and University of New Mexico, Albuquerque. Rapp, Jr., G. and C. Hill 1999 Geoarcheology: The Earth-Science Approach to Archeological Interpretation. Yale University Press, New Haven.

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