Evaluating ground‐penetrating radar antenna performance for investigating Mississippian mound construction compared with data from solid‐earth cores and magnetometry

Abstract

Mississippian mounds in the south‐eastern and mid‐continental United States often contain multiple construction stages and a diverse array of features. Investigating mound construction with excavation is expensive, logistically challenging, and sometimes politically impossible. Three mounds at the Angel site (12VG1), a Mississippian village (ca ad 1100–1450) in the lower Ohio River Valley, were investigated with non‐invasive geophysical and minimally invasive geoarchaeological methods. We compare the efficacy of two different ground‐penetrating radar (GPR) antenna frequencies (250 and 500 MHz) for detecting elements of mound construction previously identified with solid‐earth cores, magnetometry, and electrical resistance tomography. Solid‐earth cores provide stratigraphic information about mound layers and construction soils and materials with low horizontal spatial resolution. Surface magnetometry provides information on shallow features, such as buried building walls and floors at high resolution, but little information about depth. Radar profiles taken with 500 MHz and 250 MHz antennae were evaluated to determine which antenna frequencies are most suitable for detecting features and strata that had been documented using the other methods. Utilizing the solid‐earth cores for velocity correlations, the 500 MHz antenna provided the most useful information about prehistoric structures near the mound surface, but was limited by its relatively shallow penetration depth. The 250 MHz antenna was not able to resolve shallow features as clearly as the 500 MHz antenna. However, it was able to detect possible interior mound platforms and features, although without providing many details about possible buried structures. In combination, GPR, solid‐earth cores, and magnetometry provided new information about the construction of mounds at the Angel site.

Multi‐method geophysical investigation at Snow's Bend, a Mississippian platform mound

“…Putting aside some minimally invasive geophysical methods (e.g., downhole magnetic susceptibility), the most commonly used methods are GPR and ERT. GPR radargrams have been widely used to interpret mound stratigraphy, as the interfaces between construction layers and clay mantles can be identifiable depending on the attenuation of the signal and antenna used (Bigman & Seinfeld, 2017; Brannan & Bigman, 2014; Gage, 2000; Gage & Jones, 2001; Schurr et al, 2020; Seinfeld et al, 2015). For example, Seinfeld et al (2015) used GPR to identify the internal structure of the mounds at Lake Jackson, a Mississippian site in Florida.…”

SURVEY, DRILL AND EXCAVATE. Complex geoarchaeological prospection of Bronze Age mounds as a key for understanding undermound architecture. A case study from Myluvannia, Western Ukraine

“…Current archaeology uses several noninvasive methods represented mostly by geophysical prospection. The application of geophysical techniques to investigate past human activities is considerable enough to be recognized as a separate branch of science known as archaeo‐geophysics (El‐Qady & Metwaly, 2019; Malouchos et al, 2021; Sala et al, 2012; Schurr et al, 2020). Three geophysical methods—electrical resistivity of strata, ground‐penetrating radar (GPR) and magnetometry—are commonly used in archaeological prospection to provide a glimpse into the vertical stratigraphy of archaeological deposits as well as their spatial distribution.…”

The roles of macro‐ and micro‐scale geophysical investigations to guide and monitor excavations at a Middle Woodland site in northern Georgia, USA

“…Over the past decade, geophysics has proved to be a useful methodology for mapping Woodland era villages and central places in the eastern United States (Bigman & Seinfeld, 2017; Birch & Lulewicz, 2014; Green et al, 2021; Henry, 2011; Henry et al, 2014; Henry et al, 2020; Horsley et al, 2014; King et al, 2017; McKinnon & Haley, 2017; Pluckhahn et al, 2010; Royce, 2011; Thompson & Pluckhahn, 2010; Wright, 2014) generally with the goal of delineating physical community organization and selecting locations for future excavations. Monumental architecture has also been extensively investigated across the area with various geophysical and remote sensing methods (Bigman & Lanzarone, 2014; Brannan & Bigman, 2014; Burks & Cook, 2011; Garrison, 1998; Green et al, 2021; Haley, 2014; Hargrave, 2011; Henry et al, 2020; Herrmann et al, 2014; Kassabaum et al, 2014; King et al, 2011; Schurr et al, 2020; Seinfeld et al, 2015; Thompson & Pluckhahn, 2010; Welch et al, 2005). These have provided the archaeological community with a good record of expectations for responses from mound construction layers and architectural features.…”