Martta-Kaisa Olkkonen

Discrimination of Buried Objects in Impulse GPR Using Phase Retrieval Technique

This paper presents a modified signal processing technique of differentiating buried targets using impulse ground-penetrating radar. The technique is applicable to radargram; however, signal processing is carried out for each trace of the radargram separately. Every significant peak of each trace is compared with the peak of some calibration signal, for example, a signal that is reflected from the far interface of a thick rock slab. However, the calibration does not require the reference material be embedded in the medium, it can be in the air. The difference of phases between the object signal and the calibration signal is a function slowly varying with time that can be used for characterization of the buried object. The performance of the method is demonstrated in several examples using signals collected with the commercial impulse radar.

A New Microwave Asphalt Radar Rover for Thin Surface Civil Engineering Applications

Abstract This paper presents a beyond state-of-the-art, sweeping microwave asphalt radar mounted on a small radio controlled four-wheel-drive rover. The quasi-monostatic, remote-controllable radar operates at Ku-band and has an output power of +10 dBm. Detection follows the zero intermediate frequency principle. The sweep width allows for a depth resolution better than 10 mm. With its four microprocessors and laptop computer processing, the radar system can provide pavement permittivity data with an uncertainty close to 0.1. This is a considerable advancement when applying electromagnetic measurement techniques for applications where near surface or thin surface layer measurements are needed.

An Evaluation of the Permittivity of Two Different Rock Types Using Microwave Resonator and Waveguide Cutoff Principles

Abstract Methods of measuring the complex permittivity of different rock types are demonstrated in the frequency range from 6 GHz to 17 GHz. The used methods are based on the cylindrical resonator and waveguide cutoff frequency principles. This study is part of a larger research project that aims to characterize the electrical properties of asphalt for road surveying purposes. The studied rock types are metavolcanic rock with intermediate composition and pegmatite. The permittivity values gained with the resonator method are 6.2 for the metavolcanic rock and 4.5 for the pegmatite rock type, whereas the imaginary parts are 0.04 and 0.02. The permittivity values gained with the cutoff frequency method are 6.17 and 4.76 respectively. A reference measurement was made only for the metavolcanic rock in a transmission configuration with two antennas and the permittivity result was 6.21. The three different methods provide consistent permittivity values and are suitable for reliable permittivity evaluation.

Subsurface target identification using phase profiling of impulse GPR data

The problem of target discrimination in ground penetrating radar data (GPR) is addressed in this study. Formerly developed frequency-domain technique based on building separate amplitude and phase profiles for every A-scan has been modified to be suitable also for impulse GPR data. To this end, impulse radar data have been preprocessed and transformed to frequency domain. The rest of the algorithm is rather similar to the case of frequency-domain radar data. The method yields a phase profile as a function of depth that is related to the phase shift occurring in the act of reflection of the wave from inhomogeneity existing at given depth. This phase shift depends on the contrast between the target and surrounding medium and thus can be used for target characterization. The technique was used to interpret data collected over a test site, where metal bars and a plastic pipe were buried inside sand and gravel. The radar data was collected with Malâs CX11 Concrete Imaging System operating at the 1600 MHz central frequency. The images built with the use of the novel signal processing technique demonstrate its validity for recognition of some buried objects.

A new microwave asphalt radar

This article presents a new K-band asphalt radar for evaluating road pavement surface layer density during construction. The frequency range of operation is 13-17 GHz. A high frequency band is needed since the new asphalt overlays are very thin. Therefore, better resolution of the radar system is required. In this paper, the new radar system is described in detail. The first laboratory analyses of the asphalt sample are presented using the new radar. This serves the purpose of evaluating and testing the performance of the new radar measurement setup. The radar will be used later for mobile road surveying.