Enhancing the Assessment of Historic Masonry Walls Using Multi-Frequency GPR Attribute Analysis

The structural condition of historic masonry walls plays a crucial role in the conservation and management of cultural heritage assets. Moisture ingress, material degradation, and hidden internal defects often develop beneath the surface, remaining undetected by visual inspection alone. Traditional invasive inspection methods are limited by their local nature and the potential risk of damaging heritage fabric. Consequently, non-destructive testing (NDT) techniques capable of providing reliable subsurface information are essential.

Ground Penetrating Radar (GPR) has become a widely adopted non-destructive and cost-effective technique for investigating masonry structures [1-3], allowing the identification of internal heterogeneities, voids, and moisture-related anomalies. However, the interpretation of conventional GPR sections is frequently affected by signal complexity, non-uniqueness, and ambiguity, particularly when dealing with heterogeneous historic materials and varying wall thicknesses.

This study presents a multi-frequency GPR survey conducted on a historic brick masonry wall located in Walpole Park (Ealing, London, UK), a site of special historic interest. The primary objective was to assess the internal condition of the wall and investigate suspected moisture ingress. Data were acquired using ground-coupled GPR systems operating at 2 GHz and 600 MHz, including dual-polarised configurations (HH and VV), allowing a comparative evaluation of resolution and penetration depth for walls of approximately 25 cm and 55 cm thickness.

To enhance data interpretation, attribute analysis, originally developed in seismic exploration, was applied to the GPR datasets. Attributes such as Centroid Frequency (CF) and Instantaneous Frequency (IF) were extracted from both processed and unprocessed radar data. These attributes provide additional information on material properties and signal attenuation, which are strongly linked to moisture content, material heterogeneity, and structural condition. Three-dimensional visualisation of attribute volumes was employed to better delineate spatial variations within the masonry fabric.

Attribute-based representations significantly improved the clarity and interpretability of subsurface anomalies compared to conventional amplitude-based GPR images.

The findings confirm that GPR attribute analysis enhances the assessment of historic masonry structures and supports more reliable interpretation of moisture-related and structural features. The proposed workflow offers a robust, non-invasive tool for heritage conservation and condition monitoring, with potential for wider application across cultural heritage and built-environment diagnostics.

Keywords: Ground Penetrating Radar (GPR); Cultural Heritage; Masonry Inspection; Moisture Ingress; Signal Attribute Analysis

 

References

[1] Sambuelli, L., Bohm, G., Capizzi, P., Cardarelli, E., & Socco, L. V. (2011). The use of ground penetrating radar and complementary NDT techniques for the diagnostic of masonry structures. Near Surface Geophysics, 9(5), 433–447.

[2] Bianchini Ciampoli, L., Parnow, S., Tosti, F., and Benedetto, A.: Retrieving signs of buried historical road tracks by GPR data processing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16105, https://doi.org/10.5194/egusphere-egu25-16105, 2025.

[3] Catapano, I, Gennarelli, G., Ludeno, G., and Soldovieri, F., Applying Ground-Penetrating Radar and Microwave Tomography Data Processing in Cultural Heritage: State of the Art and Future Trends. IEEE Signal Processing Magazine, vol. 36, no. 4, pp. 53-61, July 2019, doi: 10.1109/MSP.2019.2895121.