Time Domain Reflectometer
Time domain reflectometer rods were installed in various locations in the subgrade and in the concrete slabs. The purpose of these gages is to measure moisture content of the medium in which they are installed. This process is indirect and gages must individually be calibrated. The method of operation is as follows: a pulse is sent to the gage. The reflection of the pulse is then obained. Analysis of the pulse reflection is made and provides a measure of the Dielectric "constant" value of the medium. Calibration equations developed in the laboratory are then used to obtain moisture content values from the dielectric values. For all gages located in the subgrade the Topps and Davis equation is used. For other gages the FAA is developing calibration equations.
Below is a plan view of the instrumented pavement section located on Runway 34R/16L at DIA. For detailed information on a specific set of sensors, click on the corresponding link below on the right.
Typical Cross Section
Typical TDR Moisture Probe