The radar data consists of a collection of waveforms representing time-delayed reflections of the transmitted pulses from subsurface dielectric interfaces. The data is collected by scanning the radar unit over the object surface and triggering the data acquisition system at uniform inter-vals so that the final waveforms lie on a square grid. This implies that some type of position encoding mechanism is needed to control the overall data acquisition. A computer-controlled mechanical system was used to conduct the experiments presented in this article. The radar data is acquired and stored in the computer's internal hard drive via the data acquisition card.
Additional software is available for further data processing and image formation.
The image-formation algorithm currently being used is based on a multifrequency diffraction tomography algorithm. Unlike conventional diffraction tomography methods in which the tomographic nature of the data is obtained from the rotation of the object, a synthetic aperture pulse-echo radar method is employed. In this method, the tomographic information is obtained from the wideband pulse that provides multiple illuminating wavelengths. Each wavelength in the received wavefield represents a different portion of the spectrum of the object distribution. The underlying propagation model is flexible enough to account for multiple layers of different materials.