  Impact sounding signal has been shown to contain information about structural
integrity flaws and subsurface objects from previous research. As
non-destructive testing (NDT) method, one of the biggest challenges in impact
sounding based inspection is the subsurface targets detection and
reconstruction. This paper presents the importance and practicability of using
solenoids to trigger impact sounding signal and using acoustic data to
reconstruct subsurface objects to address this issue. First, by taking
advantage of Visual Simultaneous Localization and Mapping (V-SLAM), we could
obtain the 3D position of the robot during the inspection. Second, our NDE
method is based on Frequency Density (FD) analysis for the Fast Fourier
Transform (FFT) of the impact sounding signal. At last, by combining the 3D
position data and acoustic data, this paper creates a 3D map to highlight the
possible subsurface objects. The experimental results demonstrate the
feasibility of the method.
