Abstract
Ground penetrating radar (GPR) has been found to be most suitable for subsurface stratigraphic and lithologic mapping. In this study, we showed its application in bathymetric study in the region where a proposed pedestrian bridge across a river channels is planned. The application of a novel digital signal processing approach applied to the GPR acquired is shown. The methodology adopted involved the acquisition of GPR data along a 100 m transect, across the river using a 200 MHz GSSI SIR equipment. The GPR data was processed using the sequence viz: 1) Dewowing 2) Filter in frequency domain 3) Custom Gain 4) Automatic gain control 5) Delete Mean trace and 6) Deconvolution. In addition, complex processing methods (Instantaneous attribute) was applied to increase interpretability of the GPR data. The performance of each processing step is compared by examining its result. The study shows that filtering in frequency domain; gain application and delete mean trace are the basic processing steps used in low noisy data acquired with GSSI equipment. From the processing, it was evident that deconvolution is very effective in removing reverberation and/or multiples from the dataset. Delete mean trace produced the best result in removing high amplitude, continuous horizontal reflections (such as direct wave) that conceals true reflections. Even though these methods were effective, each method has its own advantages and limitations. Therefore, preservation of the geological features should supersede any other motive or decision made during GPR data processing. Among the complex processing methods, Instantaneous phase proved to be most resourceful for bathymetric study. The Interpreted section revealed the base of the river at a depth of 5 m. A good knowledge of the river geometry which will help civil engineers in proper planning of the bridge footings structure was also obtained.
Highlights
Rivers have a prominent role in many contexts as a natural environment, as a transfer medium, as a physical medium, as a natural resource
We showed the processing steps followed in removing the unwanted signals from the Ground penetrating radar (GPR) data acquired over a river channel
Ground penetrating radar as a 2D subsurface imaging tool is an efficient method in locating the best position for bridge footing in the river
Summary
Rivers have a prominent role in many contexts as a natural environment, as a transfer medium, as a physical medium, as a natural resource. The process of designing a bridge requires detailed knowledge of riverbed topography (geometry of the riverbed at various spatial and temporal scales) Remote sensing technique such as Ground penetrating radar (GPR) and Bathymetric Lidar has been used to map river bathymetry [1,2,3]. Ground penetrating radar is a non invasive, non destructive electromagnetic (EM) investigation method It is mostly used in reflection mode where a short pulse EM wave is emitted via an antenna into the subsurface. The arrival time and the amplitude of the reflected signals caused by changes in materials electrical property (Dielectric permittivity and Electrical conductivity) is recorded and analyzed It provides information about both the spatial and vertical variation of the subsurface material at accuracy of few millimeters to several meters. Adepelumi and Olorunfemi[6] conducted an integrated engineering geological and geophysical investigation of the reclaimed Lekki Peninsula, Lagos, Southwest Nigeria where the subsurface stratigraphy in the eastern part of Lagos was delineated
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