بهرهگیری از توموگرافی مقاومت الکتریکی در باستانشناسی: مطالعهای با رویکرد مدلسازی عددی در نرمافزار COMSOL
محورهای موضوعی : باستانشناسی تاریخی
1 - دانشآموخته کارشناسی ارشد باستانشناسی دوران تاریخی، دانشکده هنر و معماری، دانشگاه مازندران، بابلسر.
2 - دانشجوی دکتری اپتیک و لیزر، دانشکده فیزیک، دانشگاه مازندران، بابلسر.
کلید واژه: توموگرافی مقاومتی الکتریکی, تصویربرداری زیرسطحی, تصویربرداری مقاومتی, ژئوفیزیک,
چکیده مقاله :
باستانشناسی بهعنوان دانشی میانرشتهای، همواره بهدنبال روشهایی نوین برای کاوش غیرمخرب و دقیق در لایههای زیرزمینی بوده است. یکی از روشهای نوظهور و بسیار کارآمد در این حوزه، توموگرافی مقاومت الکتریکی (ERT) است که با بهرهگیری از تغییرات مقاومت الکتریکی در زیرسطح، امکان شناسایی ساختارهای مدفون، قبرها، زیرساختها و دیگر شواهد فرهنگی را فراهم میسازد. این مقاله با تمرکز بر کاربرد باستانشناختی ERT، به تحلیل عددی این روش در محیط شبیهسازی پیشرفتهٔ نرمافزار COMSOL میپردازد. در چارچوب این پژوهش، یک مدل سهبعدی استوانهای با قطر ۴۰ متر و ارتفاع ۲۰ متر طراحی شد که در آن ۲۵ الکترود بهصورت خطی در سطح قرار گرفتند. شبیهسازی عددی انجامشده، امکان بررسی دقیق توزیع پتانسیل الکتریکی و مقاومت ویژه زیرسطح را فراهم کرده و با مقایسه نتایج با حل تحلیلی در محیط همگن، صحت عملکرد مدل ارزیابی شد. افزون بر این، تأثیر پارامترهایی همچون آرایش الکترودها، فاصله آنها و ویژگیهای فیزیکی مواد زیرسطحی بر نتایج تصویربرداری مورد تحلیل قرار گرفت. نتایج این پژوهش نشان میدهد که ترکیب روش ERT با شبیهسازی عددی، رویکردی مؤثر، غیرویرانگر و دقیق برای شناسایی ساختارهای باستانی فراهم میسازد و میتواند جایگزینی علمی و پایدار برای روشهای سنتی حفاری باشد.
Archaeology, as an interdisciplinary science, continually seeks innovative methods for accurate and non-invasive subsurface exploration. Among the emerging and highly effective techniques in this field is Electrical Resistivity Tomography (ERT), which utilizes variations in subsurface electrical resistivity to detect buried structures, graves, infrastructure, and other cultural remains. This paper focuses on the archaeological application of ERT by conducting a numerical analysis using the advanced simulation capabilities of COMSOL Multiphysics software. Within the framework of this study, a three-dimensional cylindrical model with a diameter of 40 meters and a height of 20 meters was developed, with 25 electrodes linearly arranged on the surface. The numerical simulation enabled detailed examination of electric potential distribution and subsurface resistivity, and the model’s accuracy was validated by comparison with analytical solutions in a homogeneous medium. Furthermore, the study analyzed the effects of electrode configuration, spacing, and the physical properties of subsurface materials on the imaging results. The findings demonstrate that integrating ERT with numerical simulation provides an effective, non-destructive, and precise approach for identifying archaeological features, offering a scientifically robust and sustainable alternative to traditional excavation methods.
- Introduction
Electrical Resistivity Tomography (ERT) is a geophysical subsurface investigation method based on measuring spatial variations in electrical resistivity within the ground. The technique operates by injecting a controlled electrical current into the subsurface through a set of electrodes placed on the ground surface and measuring the resulting potential differences between selected electrode pairs (Alexakis et al., 2012). These measurements allow for the reconstruction of lateral and vertical variations in apparent resistivity, which can then be interpreted to infer subsurface structures and material properties.
ERT has proven particularly effective in archaeological contexts because electrical resistivity is directly influenced by physical characteristics such as lithology, porosity, fracture density, moisture content, and the presence of voids or anthropogenic structures. Buried archaeological features—such as stone walls, foundations, graves, and infrastructure—often exhibit resistivity contrasts relative to surrounding sediments, making them detectable through resistivity imaging (Vásconez-Maza et al., 2020). Over the past decade, significant advances in field instrumentation, electrode configurations, and data inversion algorithms have enabled the development of three-dimensional ERT imaging, substantially enhancing the interpretive power of the method in archaeological research (Bianco et al., 2019).
The electrical properties measured by ERT are affected by a combination of material composition, soil saturation, and subsurface heterogeneity. Conductive materials facilitate current flow and generate distinctive resistivity signatures, allowing more precise characterization of buried features. Although ERT is often employed alongside complementary geophysical techniques such as Ground Penetrating Radar (GPR) or electromagnetic induction, its capacity to detect relatively deep subsurface structures makes it a valuable standalone tool in archaeological prospection (Bianco et al., 2019).
Standard ERT surveys typically involve linear or two-dimensional electrode arrays with regular spacing (Piroddi et al., 2020). In two-dimensional surveys, each measurement corresponds to a specific electrode separation, producing vertical resistivity sections of the subsurface (Milo et al., 2022). In contrast, three-dimensional imaging employs ring-shaped or other geometric electrode configurations to generate volumetric models of subsurface resistivity (Piroddi et al., 2020). Recent developments in probabilistic resistivity tomography, which do not rely on strong a priori assumptions about subsurface geometry, have further improved resolution and interpretive reliability (Fiore et al., 2002; Mauriello et al., 1999).
The choice of electrode configuration plays a critical role in survey outcomes. For example, dipole–dipole arrays are particularly sensitive to lateral resistivity variations and are well suited for detecting vertical structures such as walls or cavities. Electrode spacing controls the balance between resolution and depth of investigation: smaller spacings enable detection of narrow features but reduce penetration depth (Urbini et al., 2007). In challenging environments, including shallow marine settings, additional factors such as water-layer thickness and conductivity must be considered to optimize signal-to-noise ratios (Loddo et al., 2016). Through repeated archaeological validation via excavation, ERT has demonstrated its reliability in identifying buried structures with high accuracy (Cardarelli et al., 2008; Urbini et al., 2007).
- Methodology
The methodological framework of this study integrates archaeological case studies with numerical simulation to evaluate the performance and interpretive capabilities of Electrical Resistivity Tomography. First, a comprehensive review of archaeological applications of ERT was conducted, focusing on building remains, burial contexts, religious monuments, and subsurface infrastructure. These empirical examples provided the archaeological grounding for the methodological discussion.
Second, a numerical forward-modeling approach was implemented using the COMSOL Multiphysics software environment. A three-dimensional subsurface model was constructed, incorporating defined geometries, material properties, and boundary conditions. Electrical resistivity values were assigned to different subsurface zones to simulate homogeneous and simplified archaeological scenarios. The governing physical behavior of the system was described using Laplace’s equation, which relates electrical potential to resistivity distribution.
The subsurface domain was discretized using a finite-element mesh, enabling numerical solution of the governing equations under realistic conditions where analytical solutions are impractical. A linear array of 25 electrodes was modeled, with controlled current injection and potential difference measurements between selected electrode pairs. Simulated resistivity values were computed and compared with analytical solutions to assess model accuracy and reliability. Parametric analyses were then performed to evaluate the effects of electrode configuration, current frequency, and noise levels on imaging resolution.
- Discussion
3.1. Archaeological Applications of Electrical Resistivity Tomography
ERT has emerged as a highly versatile tool in archaeological prospection due to its sensitivity to subsurface heterogeneity. One of its most prominent applications is the detection of architectural remains, including stone walls, building foundations, and collapsed masonry. These features typically produce high-resistivity anomalies relative to surrounding soils, allowing clear delineation of built environments (Cozzolino et al., 2020). ERT has also proven effective in mapping ancient urban layouts, roads, and structural complexes, even in submerged or waterlogged archaeological contexts (Simyrdanis et al., 2016).
In deeply stratified archaeological landscapes, such as Near Eastern tells, ERT enables imaging of features buried beneath thick sedimentary sequences. Studies have demonstrated its effectiveness in reconstructing complex, multi-layered architectural histories and identifying deeply buried structures that are inaccessible through shallow geophysical methods (Casana et al., 2008; Novo et al., 2012).
3.2. Burial Contexts and Funerary Features
Another major application of ERT is the identification of burial features. Both simple inhumations and complex tomb architectures can be detected through characteristic resistivity contrasts. Stone-lined graves typically appear as high-resistivity anomalies, while areas associated with organic decomposition often exhibit reduced resistivity due to increased moisture retention (Berezowski et al., 2021; Matias et al., 2006). Coffin burials, in particular, may produce anomalously low resistivity signatures related to water accumulation within void spaces.
ERT has been successfully applied in both archaeological and forensic investigations, demonstrating its capacity to detect unmarked graves with minimal disturbance. These applications underscore the method’s ethical and practical advantages in sensitive burial contexts.
3.3. Historical Monuments and Religious Architecture
ERT plays a crucial role in the non-destructive investigation of standing historical monuments and religious structures. Studies conducted beneath churches and monumental buildings have revealed hidden voids, ancient wells, crypts, and subsurface structural modifications without compromising the integrity of the architecture (Tsokas et al., 2008; Tsourlos et al., 2011). Investigations at sites such as the Acropolis of Athens illustrate how ERT contributes to heritage conservation by identifying subsurface risks and undocumented features (Novo et al., 2012).
3.4. Subsurface Infrastructure and Hydraulic Systems
Ancient infrastructure systems, including aqueducts and drainage networks, represent another domain where ERT has demonstrated exceptional utility. These features may be located at considerable depths and beneath conductive surface layers, conditions under which many geophysical methods struggle. ERT’s ability to penetrate such environments enables the detection and mapping of buried infrastructure, even under challenging geological conditions (Trogu et al., 2014; Cozzolino et al., 2020).
3.5. Numerical Simulation and Sensitivity Analysis
The numerical simulations conducted in this study provide critical insights into the physical behavior of electrical currents in the subsurface and the sensitivity of ERT measurements to various parameters. A homogeneous cylindrical model with a resistivity of 100 Ω·m was used as a baseline scenario. By injecting current through designated electrodes and measuring resulting potential differences, simulated resistivity values were obtained and compared against analytical solutions, confirming the validity of the numerical approach.
Sensitivity analyses demonstrated that electrode spacing and configuration significantly influence image resolution and depth of investigation. Smaller electrode spacing enhances near-surface resolution but limits penetration depth, while larger spacing improves depth coverage at the expense of detail. Variations in current frequency and noise levels further affect data quality, emphasizing the need for optimized survey design tailored to specific archaeological objectives.
3.6. Model Geometry and Comparative Evaluation
A key outcome of this study is the comparative evaluation between cylindrical and box-shaped subsurface models. Results indicate that the cylindrical model more accurately represents subsurface behavior, producing outcomes that align more closely with expected physical responses. This improvement likely stems from better geometric conformity with realistic subsurface conditions and enhanced numerical stability. The comparison highlights the importance of selecting appropriate geometric representations and modeling assumptions when conducting ERT simulations.
- Conclusion
Electrical Resistivity Tomography has established itself as a powerful, non-invasive, and highly effective method in archaeological investigation. By enabling detailed imaging of subsurface resistivity distributions without extensive excavation, ERT offers significant advantages in identifying buried structures, stratigraphic layers, and archaeological features while minimizing disturbance to cultural heritage.
The numerical simulations conducted using COMSOL Multiphysics demonstrate that ERT is capable of accurately reproducing subsurface electrical behavior and resistivity patterns under controlled conditions. Analysis of key parameters—including electrode configuration, current frequency, noise levels, and model geometry—highlights their critical role in optimizing resolution, depth of penetration, and interpretive reliability. The results further show that selecting geometrically appropriate subsurface models, such as cylindrical representations, can substantially enhance simulation accuracy and confidence.
Overall, the integration of numerical modeling with archaeological field applications positions ERT as a robust methodological framework for subsurface exploration. Beyond feature detection, ERT contributes to informed excavation planning, risk assessment, and heritage conservation strategies. The findings of this study encourage archaeologists and geophysicists to incorporate numerical simulation alongside field surveys, particularly in complex or sensitive environments, to improve analytical outcomes while safeguarding archaeological resources.
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