GIS and Remote Sensing

Brockington and Associates has significant experience in employing both Geographic Information Systems (GIS) and Computer-aided Design (CAD) software to the understanding and evaluation of archaeological and historical resources. We currently use the latest versions of ArcGIS, ArcView, and AutoCAD. Additionally, we can integrate all other formats (such as ArcInfo, Imagine, Grass, Microstation) within our GIS systems.

Most commonly employed on archaeological and historical survey projects, and on major mitigation studies, GIS and CAD are used in three primary capacities:

  1. To aid to integrating digital archaeological and historical data with historical maps, aerial photographs, and other spatial records. Field recordation is enhanced with the use of Global Positioning Systems units (for surveys) and a Digital Total Station (for mitigation projects).
  2. To query and to summarize field data to develop analytical surfaces that allow the archaeologist or historian to make interpretations which are not visually apparent, such as allowing mapping of artifact density or preparing alternative viewshed analyses.
  3. To integrate analytical surfaces and research themes into interpretative graphics for use in reports and publications. Such graphics are of special importance for museum displays and exhibits, particularly through the use of modeling techniques and 3D visualization tools.



Figure 1
Observed loss of bank area at the Mulberry Site, South Carolina.



Figure 2
Reconstruction of the First Pensacola Lighthouse and the Keeper's Residence (ca. 1850), over the excavated features from the Navy Lodge Project.



Figure 3
Photorealistic three-dimensional reconstruction of Cherry Hill Plantation, Bryan County, Georgia (ca. 1850)



Figure 4
Conceptual model of the risk of recapture and the associated cognitive landscape for enslaved African-Americans in the Ford Plantation Project Area (mid-1800s).



Figure 5
Detail of the prehistoric probabilistic model for archaeological site locations at the Charleston Naval Weapons Station, South Carolina.

GIS modeling encompasses a diversity of projects and approaches. Some analytical studies are used to evaluate potential visual or aural effects to historic properties through visibility, buffer, and cost-distance evaluations. Examples of use of these approaches include (1) determining the visual impacts from the proposed Eisenhower Expressway at Ocmulgee National Monument using composite visibility analyses, and (2) extracting previous landscape characteristics from historic aerial photographs and maps to assess the rate of erosion at the Mulberry Site, South Carolina (Figure 1).

Other kinds of GIS modeling studies determine the nature and locations of historic structures and settlements through integrating archaeological and documentary evidence. An illustration of this approach can be seen in the identification of Civil War period encampment locations at Naval Air Station Pensacola, through interactive manipulation of three-dimensional photographic overlays. Another example is the digital reconstruction of architectural details at the first Pensacola lighthouse and keeper's residence based on identified subsurface features, photographs, and verbal descriptions (Figure 2).

GIS allows the recreation of historic landscapes and settings using three-dimensional photorealistic and virtual reality software. A key example can be found in visualizing the long sequence of historic settlement at Silk Hope, Cherry Hill, and Richmond Plantations on the Ogeechee River, Georgia, using photorealistic textures with native vegetation and period appropriate land use patterns (Figure 3).

At the forefront of theoretical GIS is our work in evaluating and visualizing historic and prehistoric "cognitive" landscapes. This is a critical area of GIS research in archaeology and can be expressed with illustrations from a project which assessed the spatial context and decision-making factors for enslaved African-Americans during the Antebellum period (Figure 4). This project illustrated how we might determine the factors leading to the choice to attempt an escape and in what context the risks of recapture appear to be overcome.

Another commonly applied modeling study is the development of GIS-based probabilistic models of prehistoric and historic human landscape usage, through the statistical and analytical evaluation of natural and cultural variables. Brockington has developed numerous "predictive models" using various intuitive, inductive or deductive strategies for projects ranging from Florida to Ohio. Our development and implementation of such models has led the way for CRM applications, and several examples stand out. Perhaps the largest archaeological predictive model developed east of the Mississippi, the combined Alabama-Coosa-Tallapoosa (ACT) and Apalachicola-Chattahoochee-Flint (ACF) basin studies for the US Army Corps of Engineers, covering most of Alabama, half of Georgia, and the Florida panhandle, were crucial components to understanding how changes in the water formulas would affect cultural resources. In a different vein, the predictive model developed for the Charleston Naval Weapons Station, South Carolina, was one of the first successful practical applications of a "deductive" model (Figure 5).

GIS and predictive modeling is at the forefront of spatial land management tool applications, and Brockington remains committed to developing new methods and new approaches that will provide an explanatory balance to a field often beset by sterile statistical correlative evaluations.

Remote Sensing

Along with GIS, Brockington and Associates has been very successful in the application of remote sensing to projects of all shapes and sizes. On the ground such work principally includes Ground Penetrating Radar (GPR), resistivity, magnetometry, and metal detecting. Additionally, more removed forms of remote sensing are employed, such as the use and analysis of high resolution true-color, black-and-white, and false-color aerial imagery, along with Light Detection and Ranging (LIDAR) and side-scanning sonar data (for underwater resources), typically provided by our engineering clients.

These non-invasive methods allow us to efficiently and quickly discover sites, features and burials. They also allow the detailed interpretation of deposits within sites or in the surrounding region. With remote sensing applications we can cover large areas of terrain or the surface of a site quickly and effectively, yet reveal many details prior to excavation.



Figure 6
Wendy Weaver operating the GPR at a site in North Augusta, South Carolina.

GPR works by the transmission of electromagnetic pulses, which travel as radar waves into the ground. The elapsed time between transmission of the waves, reflection off buried anomalies, and reception back to the surface radar antenna is then measured. Buried anomalies (such as graves, privies, and house foundations), create changes in the electrical or magnetic properties of the rock, sediment or soil or variations in water content. Reflections from the radar waves are recorded by the GPR antenna. These changes are measured in two way travel time and velocity can be determined, and thus the location, depth and shape of these anomalies (Figure 6).

Resistivity is a method of subsurface exploration whereby an electrical current is passed through the ground and the conductivity is measured between sets of electrodes set in different configurations. The raw data is collected over a large area and processed via the computer into two and three dimensional maps of electrical conductivity. These maps can then be used to generate an understanding of the nature of buried anomalies.

Magnetometry uses a different process to identify buried anomalies. A magnetometer measures minute variations in the magnetic field around it. When projected into the surface of the earth, the magnetometer can measure fluctuations as small as 1/50,000th of the earth’s magnetic field. Some buried items or features (such as fired clay) can be detected fairly easily by magnetometry, while being difficult to identify through other methods.



Figure 7
Scott Butler operating a metal detector at Cherry Hill Plantation, Richmond Hill, Georgia.

Metal detectors use a low-frequency electrical current projected into the ground which radiates back at a different phase when it encounters highly conductive material, such as metal. The receiving coil can be set to distinguish between ferrous and non-ferrous objects, as well as being adjustable for depth (Figure 7).

Remote sensing methods can be used for finding:

Most commonly, remote sensing methods are used for large scale surveys and analyses (where aerial imagery analysis is most useful), underwater surveys (where side-scanning sonar may be the only effective method of investigation), cemetery delineations, battlefields and military encampments, and data recoveries (where GPR, resistivity, magnetometry, and metal detecting all might be used in the proper context).

Currently, Brockington uses MALA Geoscience and GSSI 2000/3000 Ground Penetrating Radar devices, along with GEM-19 Overhauser Magnetometer/Gradiometers. Data is processed and analyzed with GPR Slice, ArcGIS, Surfer, and a variety of other software programs.

Georeferenced GPR images illustrating subsurface anomalies at a large village site on the Savannah River.

Photorealistic three-dimensional reconstruction of Richmond Plantation, Bryan County, Georgia (ca. 1850).