Testing a transmission line model for homogeneous subsurface media using ground penetrating radar

摘要

Ground Penetrating Radars (GPR) process electromagnetic reflections from subsurface interfaces to characterize the subsurface and detect buried targets. Our objective is to test an inversion algorithm that calculates the intrinsic impedance of subsurface media when the signal transmitted is modeled as the first or second derivative of a large bandwidth Gaussian pulse. For this purpose we model the subsurface as a transmission line with multiple segments, each having different propagating velocities and characteristic impedances. We simulate the propagation and reflection of the pulse from multilayered lossless and lossy media, and process the received signal with a rectifier and filter subsystem to estimate the impulse response. We then run the impulse response through the inversion algorithm in order to calculate the relative permittivity of each subsurface layer. We show that the algorithm is able to detect targets using the primary reflections, even though secondary reflections are sometimes required to maintain inversion stability. We also demonstrate the importance of compensating for geometric spreading losses and conductivity losses to accurately characterize each substrate layer and target. Such compensation is not trivial in experimental data where electronic range delays can be arbitrary, transmitted pulses often deviate from the theoretical models, and limited resolution can cause ambiguity in the range of the targets.