Results of radar measurements at the Cape Town International Airport


Prepared by: Alan Langman and Mike Inggs

Affiliation: UCT

Date: 5 October, 1998

Document Number: KR-0001-CTI






    This document presents the results of measurements taken at the Cape Town International Airport on Friday 3 October 1998.




    Water has been found under the surface of the runway at Cape Town International Airport. Various core samples have shown that different areas have different water saturation levels. Due to the size of the runway and the destructive nature of taking core samples - this method of providing the required understanding of the water problem is not feasible.

    Ground Penetrating Radar provides a possible alternative. It is for this reason that the measurements presented in this report were requested.

    The report presents the processed images of the radar data collected a various points along the runway. The first three sets of results - present the radar data as 2D images scaled using different maximum and minimum end points.

    The final graph presents a measure of the energy reflected from the subsurface targets.

    Radar Equipment



    The radar equipment used was a 1-2GHz stepped frequency continuous wave radar. It was configured to take 100 frequency steps over the radar bandwidth. If we assume that the mean permittivity of the subsurface medium is 9, then the radar resolution in the ground is approximately 5cm.

    Process Radar Images



    The raw radar data was processed using standard Discrete Fourier Processing techniques. The data was interpolated to provide better images. Three sets of results are presented. Each set consists of an image of the processed data from each of the measurement sites. The data in each set various only in the scaling end points used. In each plot, the horisontal axis is in metres, and the vertical axis in metres, assuming a permittivity of 9.

      Figure 1: Each image scaled to the maximum and minimum value of all profiles

      Figure 2: Each image scaled to its own maximum and minimum value

      Figure 3. Each image scaled to its own average maximum and minimum values.

    The maximum and minimum were determined by calculating the average of these endpoints from each of the range profiles.

    Radar returned power

Increased water saturation in a layer of a subsurface medium increases the permittivity of that layer. This will result in a greater dielectric contrast between layers and hence the layer will reflect more energy back to the radar. Figure 1 shows the result of simple processing to extract this information.


Figure 4: For each profile, the total reflected enery, plotted for each transect.