Ground Penetrating Research Articles

Foreword to the Special Issue on Civil and Environmental Engineering Applications of Ground Penetrating Radar

This Special Issue in Near Surface Geophysics (NSG) on Civil and Environmental Engineering Applications of Ground Penetrating Radar is organized in the dual frame of the GI3.1 Session “Civil Engineering Applications of Ground Penetrating Radar”, which is held yearly within the General Assembly of the European Geosciences Union (EGU), and the EU-funded COST Action TU1208 “Civil Engineering Applications of Ground Penetrating Radar”.

ROSETTA lander Philae: Touch-down reconstruction

The landing of the ROSETTA-mission lander Philae on November 12th 2014 on Comet 67P/Churyumov-Gerasimenko was planned as a descent with passive landing and anchoring by harpoons at touch-down. Actually the lander was not fixed at touch-down to the ground due to failing harpoons. The lander internal damper was actuated at touch-down for 42.6mm with a speed of 0.08m/s while the lander touch-down speed was 1m/s. The kinetic energy before touch-down was 50J, 45J were dissipated by the lander internal damper and by ground penetration at touch-down, and 5J kinetic energy are left after touch-down (0.325m/s speed). Most kinetic energy was dissipated by ground penetration (41J) while only 4J are dissipated by the lander internal damper. Based on these data, a value for a constant compressive soil-strength of between 1.55kPa and 1.8kPa is calculated.This paper focuses on the reconstruction of the touch-down at Agilkia over a period of around 20s from first ground contact to lift-off again. After rebound Philae left a strange pattern on ground documented by the OSIRIS Narrow Angle Camera (NAC). The analysis shows, that the touch-down was not just a simple damped reflection on the surface. Instead the lander had repeated contacts with the surface over a period of about 20s±10s.This paper discusses scenarios for the reconstruction of the landing sequence based on the data available and on computer simulations. Simulations are performed with a dedicated mechanical multi-body model of the lander, which was validated previously in numerous ground tests. The SIMPACK simulation software was used, including the option to set forces at the feet to the ground. The outgoing velocity vector is mostly influenced by the timing of the ground contact of the different feet. It turns out that ground friction during damping has strong impact on the lander outgoing velocity, on its rotation, and on its nutation. After the end of damping, the attitude of the lander can be strongly changed by the additional ground contacts even with the flywheel still running inside the lander.The simulation shows that the outbound velocity vector and the lander rotation were formed immediately at touch-down during the first 1.5s. The outbound velocity vector is found to be formed by the ground slope and the lander damping characteristic, especially the nearly horizontal flight out.

Mapping subvertical discontinuities in rock cuts using a 400-MHz ground penetrating radar antenna

Hidden subvertical discontinuities oriented parallel to subparallel to the exposed faces of outcropping sandstone were effectively mapped at three different study sites in central Missouri using a ground-penetrating radar system (GPR) equipped with a 400-MHz monostatic antenna and a survey wheel. At each site, a suite of 2-D ground-penetrating radar profiles were acquired along multiple closely spaced traverses on relatively smooth exposed rock surfaces. Time-zero correction was applied to the raw GPR data which were then processed using band-pass filtering, range and display gain, color transformation, and deconvolution techniques. Pseudo 3D images of each identified discontinuity at each site were constructed based on the interpretation of the nonmigrated ground-penetrating radar profiles. These pseudo 3D images were hand-migrated and transformed into true 3D images which depict variable depths at “perpendicular horizontal distance” to each discontinuity relative to the exposed rock face. The results demonstrate that GPR can be used to detect and map hidden discontinuities. This information can then be used for rock slope stability analysis and rock engineering purposes.

Fault displacement accumulation and slip rate variability within the Taupo Rift (New Zealand) based on trench and 3‐D ground‐penetrating radar data

In offshore regions, studies based on densely spaced reflection seismic data tied to stratigraphic logs demonstrate that active faults can have variable displacement rates over relatively short distances and short time intervals. Here, we demonstrate how high‐resolution 3‐D ground‐penetrating (GPR) data tied to trench‐derived stratigraphic logs provide similar information for active faults in onshore regions. To investigate recent (≤24.4 ka) fault activity within the Taupo Rift of New Zealand, we analyze 3‐D GPR data acquired over 10 fault strands within the Maleme fault zone. After correlating three prominent GPR reflection horizons with three faulted chronostratigraphic units observed within a trench, we extrapolate the geometries of the horizons over a ∼150 × 250 m area of the fault zone and determine slip accumulation patterns and rates. Profiles of cumulative fault displacement measured for horizons older than 12.5 ka exhibit characteristic displacement distributions. By calculating average cumulative displacements with time for five practically complete fault strands, we obtain robust slip rate estimates. Slip rates are variable for time intervals ≤12.5 ka long, suggesting that at least four earthquakes are required for these faults to exhibit uniform slip rates characteristic of their long‐term behavior.

Ultra wideband pulse generation using microstrip coupled lines

AbstractIn this article, a novel ultra wideband (UWB) pulse generator using microstrip coupled lines (MCL) is described. The MCL circuit generates an UWB pulse which can used both in UWB communication transmitter and receiver circuits as well as ground penetrating and wall through radars. The proposed circuit formed by microstrip coupled lines and terminations generates an UWB pulse from one of the output of the microstrip couple lines. Different bandwidth pulses from the circuit can be obtained by adjusting the length of the microstrip lines. An example circuit is implemented on an FR4 substrate with dielectric constant of εr = 4.6. The length of the microstrip line was set to 9.3 cm, and pulse duration of 235 ps is obtained. This corresponds to a Gaussian pulse with 4.3 GHz bandwidth at the center frequency of 2.15 GHz. Time and frequency measurements results are presented for time waveform and |S21| of the circuit, respectively. The circuit is low cost and can be easily implemented for UWB applications. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 944–949, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24223

Mutual interference and low probability of interception capabilities of noise radar

Recently, there has been considerable interest in noise radar over a wide spectrum of applications, such as through-wall surveillance, tracking, Doppler estimation, polarimetry, interferometry, ground penetrating or subsurface profiling, detection, synthetic aperture radar (SAR) imaging, inverse SAR imaging, foliage penetration imaging etc. Major advantages of using noise in the transmit signal are its inherent immunity from radio frequency and electromagnetic interference, improved spectrum efficiency, and hostile jamming as well as being very difficult to detect. The basic theory of digital signal processing in noise radar design is treated. The theory supports the use of noise waveforms for radar detection and imaging in such applications as covert military surveillance and reconnaissance. It is shown that by using wideband noise waveforms, one can achieve high resolution and reduced range estimation ambiguity. Mutual interference and low probability of interception capabilities of noise radar are also evaluated. The simulation results show the usefulness of the noise radar technology to improve on conventional radars.

Potential Effects of the Ionosphere on Space-Based SAR Imaging

There has been a considerable interest in the use of lower frequency (VHF/UHF) space-based synthetic aperture radar (SAR) for realizing the foliage and ground penetration. The phase perturbation, signal distortion and imaging resolution degradation by the ionosphere will be particularly severe, however the model is not yet well established and still needs to be further studied. In this paper, on the basis of possible improvements for the model proposed by Ishimaru and others, potential ionospheric effects on SAR imaging are evaluated. First, for analyzing azimuthal resolution, we apply the fourth moment recently obtained in general case of strong fluctuation regimes, which is expected to give results for wider conditions. The Gaussian approximation was used in the previous model; however it is only valid in the fully saturated regimes. Second, for analyzing image shift and distortion, besides group delay, the higher-order dispersion is considered. Third, for discussing range resolution degraded due to pulse broadening, besides the dispersion, the multiple scattering of ionospheric turbulence is studied. Fourth, the Faraday rotation effect is analyzed. Numerical simulations are shown using ionospheric turbulence spectrum and TEC inferred from the International Reference Ionosphere (IRI) and satellite beacon observations.

A New Approach to Mars Ionosphere Characterisation

Abstract| Recently in order to investigate the distribution of water, liquid and solid, in theupper portions of the Martian’s crust, two difierent instruments are operatives, the Mars Ad-vanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and the SHAallow RADar(SHARAD). The secondary objective of the MARSIS instrument is the Mars Ionosphere charac-terisation through the Active Ionosphere Sounding (AIS) sensor. This operative mode presentsthe frequency agility capability in order to estimate the Mars ionosphere spectral properties. Thismethod allows the sounding of the ionosphere flrst layer only. However another method to char-acterise the Mars ionosphere can be used. Here will be presented a new ionosphere data inversionapproach using the ground penetrating (GPR) data in order to remove the data instability andthe solutions uncertainly. After the analytical data inversion formulation will be evaluated theperformances of the method and its applicability. Finally, will be presented an application to theexperimental data in order to test the proposed ionosphere data inversion method.1. INTRODUCTION

Prediction of the effects of soil and target properties on the antipersonnel landmine detection performance of ground-penetrating radar: A Colombian case study

The performance of ground-penetrating (GPR) radar is determined fundamentally by the soil electromagnetic (EM) properties and the target characteristics. In this paper, we predict the effects of such properties on the antipersonnel (AP) landmine detection performance of GPR in a Colombian scenario. Firstly, we use available soil geophysical information in existing pedotransfer models to calculate soil EM properties. The latter are included in a two-dimensional (2D), finite-difference time-domain (FDTD) modeling program in conjunction with the characteristics of AP landmines to calculate the buried target reflection. The approach is applied to two soils selected among Colombian mine-affected areas, and several local improvised explosive devices (IEDs) and AP landmines are modeled as targets. The signatures from such targets buried in the selected soils are predicted, considering different conditions. Finally, we show how the GPR can contribute in detecting low- and non-metallic targets in these Colombian soils. Such a system could be quite adequate for complementing humanitarian landmine detection by metal detectors.

Assessing sensor effects and effects of leaf-off and leaf-on canopy conditions on biophysical stand properties derived from small-footprint airborne laser data

Canopy height distributions were created from small-footprint airborne laser scanner data collected over 51 georeferenced field sample plots with a size of 232.9 m 2 and 27 large test plots with an average size of 3435 m 2. Laser data were acquired under leaf-on and leaf-off canopy conditions. The plots covered stand conditions from young forest to mature forest. The plots were divided into two categories, i.e., coniferous forest dominated by spruce and pine, and mixed forest with an average proportion of deciduous species of 31–42%. Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were computed from the laser-derived canopy height distributions. In the mixed forest, corresponding metrics derived from the two laser data acquisitions were compared. In general, canopy metrics derived from the last returns were more affected by canopy conditions than the first return data. Furthermore, canopy height measures of the lower and intermediate parts of the canopy were more affected than maximum canopy height, and the variability of the height distribution tended to increase from leaf-on to leaf-off conditions. The coniferous plots were used to demonstrate to what extent canopy properties derived from airborne lasers may be affected by sensor-specific characteristics. The same laser system was used during the two acquisitions, but the repetition frequency was upgraded from 10 to 33 kHz in between the two missions. Comparison of the two acquisitions showed that the first return measurements of canopy height tended to be unaffected or shifted somewhat upwards by system upgrade and ground penetration was reduced, whereas the last return data indicated unaffected or downwards shifted canopy heights and increased penetration.

"Mathematical Modeling of Physical Systems": An Introduction

"Mathematical Modeling of Physical Systems": An Introduction

A Full Wave Three Dimensional Analysis of Forest Remote Sensing Using VHF Electromagnetic Wave

A forest made of an infinite biperiodic array of trees over a lossy ground, is illuminated by a linearly polarized electromagnetic plane wave in the range of 20 to 90 MHz. Due to the ratio of the wavelength to the array period, only the specular mode is propagative. Therefore, a reflection coefficient is computed and not a backscattering coefficient. It is obtained by means of a full wave approach, based on an integral representation of the electric field. This approach takes into account all possible interactions between each component of the medium as well as ground penetration and provides full information on the phase of the scattered field. Two models of the forest are developed, the two layers one where trees are separated and the four layers one whee the canopy is replaced by an equivalent homogeneous medium. The low frequency (VHF) used here make this homogenization possible and allows one to consider trees with simple shape, the wave being unable to sense details of a tree.

Reconnaissance with slant plane circular SAR imaging

This paper presents a method for imaging from the slant plane data collected by a synthetic aperture radar (SAR) over the full rotation or a partial segment of a circular flight path. A Fourier analysis for the Green's function of the imaging system is provided. This analysis is the basis of an inversion for slant plane circular SAR data. The reconstruction algorithm and resolution for this SAR system are outlined. It is shown that the slant plane circular SAR, unlike the slant plane linear SAR, has the capability to extract three-dimensional imaging information of a target scene. The merits of the algorithm are demonstrated via a simulated target whose ultra wideband foliage penetrating (FOPEN) or ground penetrating (GPEN) ultrahigh frequency (UHF) radar signature varies with the radar's aspect angle.

Ultra-wideband ground-penetrating radar for the detection of buried metallic mines

The suitability of ultra-wideband ground-penetrating radar as a tool for the detection of buried metallic mines is explored in this paper. The analysis centers around a 200-800 MHz, dual-polarized ground penetrating radar (GPR) designed and built by SRI International. The analysis consisted of fusing the images from the dual polarizations into a single image to enhance the target objects and suppress clutter. Results are shown for several variations of a Mahalanobis-based fusion technique, and "soft decision" minefield detection results based upon Monte Carlo statistical techniques are also presented. Although relatively few scenes were analyzed, these results show that the dual-polarized GPR is potentially very effective at finding buried mines and minefields.

Use of airborne electromagnetic methods for resource mapping

Airborne electromagnetic (AEM) methods complement spaceborne remote sensing techniques. AEM surveys carried out from low flying aircraft are capable of detecting geological structures not visible on the surface. The flight height of AEM systems above the ground ranges from 30 to 120 m. Most systems generate primary EM fields by using a loop transmitter; conducting coils are used as antenna to measure the secondary magnetic field caused by conductive inhomogeneities in the ground. The frequency used in AEM surveys (100 Hz to 50 kHz) allows ground penetration in excess of 100 m. At present, two types of AEM systems are widely used: helicopter, frequency-domain, and fixed-wing, towed-bird, time-domain. The most common survey products are apparent conductivity maps. AEM methods are extensively used in prospecting for base and precious metal deposits, kimberlites, uranium, and also in geological mapping, groundwater exploration and environmental investigations.

Wind tunnel studies of the air flow and gaseous plume diffusion in the leading edge and downstream regions of a model forest

A model forest canopy is designed to simulate meteorological characteristics of a typical live forest. Velocity and gaseous plume behavior are measured. Flow properties are compared with recent field measurements. Ground penetration in the initial fetch region resulted in strikingly different streamline motion when compared to wind motions within the equilibrium regions. Measured values of the vertical eddy diffusion coefficient are shown to predict plume behavior in the equilibrium region if a correction is included for the ratio K y K z > 1.0 . Ventilation of an elevated line source into the canopy region is compared with a simple one-dimensional model.

GAMMA DOSE IN A HOLE IN A UNIFORMLY CONTAMINATED PLANE: CONTRIBUTION BY GROUND PENETRATION

A cylindrical hole in a uniformly gamma -contaminated plane (e.g., a foxhole in a level field) is considered. The gamma dose from ground penetration is measured as a function of depth in the hole, using a Cs/sup 137/ source. Skyshine effects are not measured. (T. F.H.)