Geophysical data fusion of ground-penetrating radar and magnetic datasets using 2D wavelet transform and singular value decomposition

Abstract

This work addresses the problem of the lack of perceptibility that geophysical data may have. Data fusion allows us to combine datasets, providing an improved and more informative source of information about structures buried in the ground. After testing different approaches, a strategy was developed using ground-penetrating radar and magnetic datasets collected over the same area. Data collected at the Roman Villa of Pisões (Beja, Portugal), which is a place of easy application of geophysical methods, were used to test the method, but with problems caused by the properties of the soil. The approach was based on processing operations that allow the fusion of images obtained by different equipment widely used in medical imaging for tumor detection and image processing. The goal is to create an improved image with data fusion that has higher quality than the input images, allowing a better understanding of the object of the study. The approach is composed of two stages: pre-processing and data fusion. Pre-processing is applied to enhance the input data. It consists of removing background noise through singular value decomposition applied in the spectral domain. Then the calculation of the data entropy will highlight the differences corresponding to the spatial alignments compatible with buried structures. Then, both entropy maps of the two datasets are fused in the second processing step to produce the final image. This step involves applying the 2D wavelet transform to each entropy map, decomposing them into sub-bands. Algorithms to calculate multiresolution singular value decomposition and the image gradient are applied to the sub-bands. The processed sub-band pairs are then fused using specific fusion rules. The fused image is obtained by applying the inverse of the wavelet transform. Data fusion with the proposed approach allows us to obtain a detailed image that is sharper and of better quality than the input datasets. The increase in sharpness and quality can be quantified through the sharpness index and the BRISQUE quality index in several steps of the processing. The obtained values confirm the graphical results. Images produced by the proposed data fusion approach suggest that the perceptibility has increased, allowing us to provide conclusions about the existence of buried structures.

Studying the water supply system of the Roman villa of Pisões (Beja, Portugal) using ground-penetrating radar and geospatial methods

“…The water supply must come from the northwest. This source of water to the inner part of the villa is compatible with the magnetic results shown in Figure 2 [15,16]. In this sector, anomaly alignments are visible that could correspond to conduits.…”

“…In 2017, several geophysical surveys have been carried out with different methods to prospect the subsurface and assess the state of conservation of some structures. Between 2018 and 2020, magnetic (vertical gradient mode) and ground-penetrating radar (GPR) surveys were carried out in several sectors around and inside the pars urbana (Figure 2) [14][15][16]. In 2017, several geophysical surveys have been carried out with different methods to prospect the subsurface and assess the state of conservation of some structures.…”

Assessing Forest-Change-Induced Carbon Storage Dynamics by Integrating GF-1 Image and Localized Allometric Growth Equations in Jiangning District, Nanjing, Eastern China (2017–2020)

“…These fusion algorithms were implemented in ENVI and Matlab packages. The evaluation of the final fused image quality is an extremely important step in the process of image fusion [56]. Generally, the evaluation includes the intuitive subjective qualitative evaluation by human visual observation and the objective quantitative evaluation by calculating quantitative statistical indicators [57,58].…”

Studying the Water Supply System of the Roman Villa of Pisões (Beja, Portugal) Using Ground-Penetrating Radar and Geospatial Methods

“…In 2017, several geophysical surveys have been carried out with different methods to prospect the subsurface and assess the state of conservation of some structures. Between 2018 and 2020 was carried out a magnetic survey (vertical gradient mode) and groundpenetrating radar (GPR) in several sectors around the pars urbana (Figure 2) [14][15][16]. In the context of this work, we would like to know how the water supply and its distribution for the hydraulic elements of the villa were articulated.…”