Abstract
This paper focuses on the use of the Canny edge detector as the first step of an advanced imaging algorithm for automated detection of hyperbolic reflections in ground-penetrating radar (GPR) data. Since the imaging algorithm aims to work in real time; particular attention is paid to its computational efficiency. Various alternative criteria are designed and examined, to fasten the procedure by eliminating unnecessary edge pixels from Canny-processed data, before such data go through the subsequent steps of the detection algorithm. The effectiveness and reliability of the proposed methodology are tested on a wide set of synthetic and experimental radargrams with promising results. The finite-difference time-domain simulator gprMax is used to generate synthetic radargrams for the tests, while the real radargrams come from GPR surveys carried out by the authors in urban areas. The imaging algorithm is implemented in MATLAB.
Highlights
Ground-penetrating radar (GPR) is the most effective and mature non-destructive inspection method for the detection of underground objects and for the high-resolution imaging of soil structures [1].Among its numerous applications in different fields, ground-penetrating radar (GPR) enables the localization and characterization of hidden utilities, even when the signal-to-noise ratio is quite low [2,3,4]
The research work presented in this paper investigated the use of the Canny edge detector in the initial stage of Automated Point Extraction from Radargrams (APEX), a previously proposed advanced algorithm for the automatic detection and characterization of hyperbolic reflections in ground-penetrating radar (GPR) radargrams
The implementation solution described in this paper largely decreases the number of unnecessary edge pixels in Canny edge processed radargrams and correctly retains edge pixels that are in the vicinity of hyperbolic reflections’ apices
Summary
Ground-penetrating radar (GPR) is the most effective and mature non-destructive inspection method for the detection of underground objects and for the high-resolution imaging of soil structures [1].Among its numerous applications in different fields, GPR enables the localization (position, depth) and characterization (size, material) of hidden utilities, even when the signal-to-noise ratio is quite low [2,3,4]. The penetration of GPR signals in the soil is limited by electromagnetic emission restrictions established by law, in addition to being strongly dependent on the frequency band of the employed antennas and environmental conditions, which implies that sometimes deep services cannot be found. To speed up the execution of APEX or other algorithms for automated hyperbola detection and characterization, it is obviously useful to eliminate as many unimportant pixels as possible from the radargram under test, in the initial stage of the procedure; Canny edge detector looks like an excellent candidate to achieve this objective. An example of application of Canny edge detector to an experimental GPR radargram is presented in Figure 2 (the edge pixels found by the Canny operator are represented in black and superimposed case a).
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