Modeling and Simulation of Low Frequency Subsurface Radar Imaging in Permafrost

K Van Den Doel,G Stove

doi:10.13189/csit.2018.060302

Abstract

We describe simulated low frequency subsurface radar scans targeting the detection of a liquid water layer, or some other reflector such as conductive sulfides, under permafrost. A finite-difference time-domain (FDTD) and ray tracing simulation framework is used to model measurements and data analysis at depths from 350m to 800m. Operating characteristics such as pulse shape and noise levels of the measurement apparatus were obtained from an existing commercial radar scanning system. Results were used to test and optimize data analysis methods, predict maximum detection depth under realistic time constraints, and guide experimental design parameters such as the amount of replications required for denoising and length of the wide angle reflection and refraction (WARR) scan lines used for velocity estimation.

Highlights

Applications of ground penetrating radar [1, 2] are currently mostly limited to shallow depths of a few tens of meters, because of the strong attenuation of radio waves in most subsurface materials at a typical frequency range of 20 − 1000MHz
In this article we present results of simulations of scans with a low frequency pulsed radar system through permafrost
To estimate velocity we perform a wide angle reflection and refraction (WARR) [11] scan, where data is acquired with transmitter and receiver at varying distances

Summary

INTRODUCTION

Applications of ground penetrating radar [1, 2] are currently mostly limited to shallow depths of a few tens of meters, because of the strong attenuation of radio waves in most subsurface materials at a typical frequency range of 20 − 1000MHz. In Stare scans transmitter and receiver are placed about 1m apart on the surface and reflections from transmitted pulses are measured repeatedly and stacked (averaged) for denoising. To estimate velocity we perform a WARR [11] scan, where data is acquired with transmitter and receiver at varying distances. Using triangulation methods such as normal move out analysis or velocity spectrum analysis allows the estimation of average velocity at a specific reflection time. Results are used to test efficacy of data analysis methods, determine the effect of backscatter caused by irregularities in the ground, estimate how much stacking is required, and estimate maximum achievable penetration depth with the modeled system

Wave propagation model

Ground models

Simulation results

Findings

CONCLUSIONS