User's Manual
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4 Introduction
4.1 Overview
This document provides the operating and configuration instructions for the Radar Ballast
Inspection Tool (RABIT). The RABIT provides non-destructive measurements of ballast fouling
and moisture over a 10 crib area of investigation. The scanner utilizes cutting-edge radar
technology to measure ballast condition in the field without invasive digging or physical
sampling. The system is comprised of the scanner unit and a tablet computer, and has been
designed so that no cables are used in order to increase ease of use and reliability. The
scanner also contains a GPS receiver so that reports of scan results are geo-referenced. The
entire system is stored rugged shipping case is designed for shipping and transport in field
situations.
The system consists of the following components.
1. A hard shell shipping container with custom foam inserts for the system
components.
2. Battery chargers for the RABIT and the tablet computer.
3. The sensor unit with GPR and GPS sensors.
4. Tablet computer (may be provided separately).
4.2 Theory of Operation
The RABIT uses ground penetrating radar (GPR) to characterize the surface beneath the
scanner unit. The scanner sends low-energy impulses of electromagnetic (EM) energy into the
subsurface and subsequently some energy is reflected back towards the sensor unit. The
characteristics of reflected energy depend on the makeup of the ballast, tie geometry, and sub-
surface layering. The ballast properties depend on the EM properties of the aggregate, the void
filling material (i.e. fouling), and moisture. The characteristics of reflected waves are also
affected by tie type (timber or concrete), tie geometry, and the layer geometry. The sub-surface
layers (ballast, sub-ballast, and sub-grade) also have varying material types, varying
Figure 1: Radar Ballast Inspection Tool (RABIT).