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A geophysical exploration employing ground‐penetrating radar (GPR) and electrical resistivity tomography (ERT) was conducted at the Western Cemetery, Giza, Egypt, in 2021–23 by a joint research team of Higashi Nippon International University, Tohoku University and the National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Egypt. We believe we found an anomaly: a combination of a shallow structure connected to a deeper structure. The shallow structure, which is L‐shaped in the horizontal plane, 10 m by 10 m, was clearly imaged by GPR. It seems to have been filled with sand, which means it was backfilled after it was constructed. It may have been an entrance to the deeper structure. Its depth is of up to 2 m, measured from the ground surface. Below this structure, ERT reveals a highly electrically resistive anomaly, which extends over an area of about 10 m by 10 m. The depth of the structure is about 5–10 m below the surface. Electrically resistive material in a sand dune can be a mixture of sand and gravel, including sparse spacing or air voids within it. Neither GPR nor ERT could identify the properties of the anomaly. [ABSTRACT FROM AUTHOR]

To investigate a thin layer, we conducted borehole radar measurements at the GPR facility of Tohoku University, Japan. Both zero-offset profiling and tomography measurements were used to obtain water content distributions. Analyzing first arrival times with amplitudes, we found that a borehole radar can detect velocity changes caused by a high-water content, which acts as an electromagnetic waveguide. We conducted a 3D FDTD simulation and confirmed that the EM wave propagates as a guided wave in a thin layer related to antenna frequency. We determined a thin geological layer compared to an antenna frequency that cannot be detected by reflection measurement due to the poor radar resolution. By comparing the simulated data with measurement data, we could determine the geological boundary between host layers and a thin layer with high water content. In contrast, both the amplitude and the travel time of direct waves are affected by antenna positions and electrical parameters, including permittivity and conductivity. A vertical velocity profile was obtained by combining complementary zero-offset profiling and tomography data, which can be used to investigate water content distribution. The low-velocity thin layer was characterised by amplitude attenuation and late arrival time. [ABSTRACT FROM AUTHOR]

Ground-based radar interferometry is capable of measuring target displacement to sub-mm accuracy. W-band ground-based radar has recently been investigated as a potential application for structural health monitoring. On the other hand, the application of W-band ground-based radar for natural slope monitoring is considered in this study due to its advantages in portability and recent cost-effective solutions. In radar interferometry, atmospheric phase screen (APS) is the most relevant phase disturbance that should be corrected for accurate displacement measurement. However, the APS effects in W-band radar interferometry have rarely been discussed. In this context, we study and evaluate the impacts of APS and its potential correction methods for 79 GHz ground-based radar interferometry using multiple-input and multiple-output (MIMO) radar. This paper presents an experimental investigation of a 79 GHz radar system using two types of field experiments conducted in an open flat field and a quarry site. In addition to the W-band radar system, a Ku-band (17 GHz) ground-based synthetic aperture radar (GB-SAR) system was jointly tested to compare different operating frequency bands. The result confirmed the accurate displacement estimation capability of the 79 GHz radar with an appropriate APS correction. [ABSTRACT FROM AUTHOR]

In this paper, an efficient and accurate imaging algorithm is presented for Ground-Based Synthetic Aperture Radar (GB-SAR) or other radar systems that could be formed by a physical or synthetic linear aperture. The imaging algorithm is based on the fractional Fourier transform (FrFT) for the azimuth compression. A mathematical framework is derived according to the projection of a sample reflectivity image onto the pseudopolar coordinate, and its implementation was presented. With the data acquisition geometry and the pseudopolar imaging coordinate, the phase of a point target can be expressed as a quadratic phase exponential. It makes that only 1-D FrFT is needed for the azimuth compression of the time-domain backscatter data for the GB-SAR imaging problem. By further research, the optimal transformation order that represents the spatial frequency changes by the FrFT was given subsequently. Taking advantage of this optimal representation, the proposed approach avoids the large calculation that occurs in the time-domain back projection (TDBP). Comparing to the far-field pseudopolar format algorithm (FPFA), the accuracy of the proposed algorithm is much improved. Meanwhile, the proposed approach holds almost the same computational cost and complexity as the FPFA. The proposed approach keeps the advantages of the imaging quality of the TDBP and the computational cost of the FPFA that are two important aspects of the GB-SAR applications. Both the numerical simulation and the field GB-SAR experiment show that the algorithm is more suitable for the high-precision GB-SAR imaging, especially for the near field. [ABSTRACT FROM AUTHOR]

In this paper, we discuss about the near range radar applied to various environmental applications and disaster mitigation issues. Synthetic aperture radar (SAR) processing or migration is the key technology in near range radar imaging, which can be used in ground penetrating radar (GPR) and ground-based synthetic aperture radar (GB-SAR). We demonstrate some applications which include GPR for humanitarian demining, GPR for archaeological survey, GB-SAR for landslide monitoring and nondestructive inspection of wooden buildings. We also demonstrate a new array GPR system 'Yakumo', which was used for archaeological survey for demonstration of advanced multi-static radar signal processing for better radar imaging. [ABSTRACT FROM AUTHOR]

Abstract: We present a ground penetrating radar (GPR) system, which uses an antenna array for in situ measurements of the thickness and dielectric permittivity of an asphalt pavement layer. We calibrated the antenna array by considering the antenna phase center and the antenna offset. The results of the laboratory measurements demonstrate that the proposed calibration method can greatly improve the accuracy of the velocity and thickness estimations when compared with the conventional method. A field measurement conducted on a highway pavement shows that the error of the thickness estimation of the asphalt layer is less than 6mm (10%). [Copyright &y& Elsevier]

This paper explores the use of full polarimetric synthetic aperture radar (PolSAR) images for tsunami damage investigation from the polarimetric viewpoint. The great tsunami induced by the earthquake of March 11th, 2011, which occurred beneath the Pacific off the northeastern coast of Japan, is adopted as the study case using the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar multitemporal PolSAR images. The polarimetric scattering mechanism changes were quantitatively examined with model-based decomposition. It is clear that the observed reduction in the double-bounce scattering was due to a change into odd-bounce scattering, since a number of buildings were completely washed away, leaving relatively a rough surface. Polarization orientation (PO) angles in built-up areas are also investigated. After the tsunami, PO angle distributions from damaged areas spread to a wider range and fluctuated more strongly than those from the before-tsunami period. Two polarimetric indicators are proposed for damage level discrimination at the city block scale. One is the ratio of the dominant double-bounce scattering mechanism observed after-tsunami to that observed before-tsunami, which can directly reflect the amount of destroyed ground-wall structures in built-up areas. The second indicator is the standard deviation of the PO angle differences, which is used to interpret the homogeneity reduction of PO angles. Experimental results from after- and before-tsunami comparisons validate the efficiency of these indexes, since the built-up areas with different damage levels can be well discriminated. In addition, comparisons between before-tsunami pairs further confirm the stability of the two polarimetric indexes over a long temporal duration. These interesting results also demonstrate the importance of full polarimetric information for natural disaster assessment. [ABSTRACT FROM PUBLISHER]

Two design methods of a filter in a frequency-spatial frequency (f-k) domain have been developed for bistatic ground penetrating radar. The proposed methods suppress the direct wave, which causes significant artifacts in radar images, and are evaluated by laboratory measurements. Because the geometric positions of a transmitting antenna and a receiving antenna are not fixed, the suppression of a direct wave is an important issue. Then, we propose an f-k filtering approach for the solution, and present two methods to design the f-k filter. Both methods use a difference of an apparent horizontal velocity between a direct wave and a reflection from a target, and work automatically from position information of a transmitting antenna and a receiving antenna. One method is to mask an f-k spectrum in a region where a spectrum of the direct wave is distributed. The region is defined from the maximum and the minimum apparent horizontal velocity of the direct wave, which are calculated from the location of the transmitting antenna and the scanning area of the receiver. As for the other method, the most essential point is applying a time shift to eliminate a difference of an arrival time of a direct wave, where the time shift is calculated beforehand from the location of the transmitting antenna and the receiving antenna. Then, anapparent horizontal velocity of the direct wave becomes infinitely large due to the time shift. Thus, the f-k spectrum of the direct wave concentrates around a frequency axis because its slope is infinitely large. Then, a filter to reject the dc component in the spatial frequency direction is applied. Both methods are applied to an experimental data set which is acquired by a bistatic radar measurement to detect a buried landmine model with a depth of 10 cm. In addition, it is confirmed that they can suppress the undesired fluctuation of the images nearly one-tenth and help the reliable detection of a buried object. [ABSTRACT FROM AUTHOR]

Two design methods of a filter in a frequency--spatial frequency (f-k) domain have been developed for bistatic ground penetrating radar. The proposed methods suppress the direct wave, which causes significant artifacts in radar images, and are evaluated by laboratory measurements. Because the geometric positions of a transmitting antenna and a receiving antenna are not fixed, the suppression of a direct wave is an important issue. Then, we propose an f-k filtering approach for the solution, and present two methods to design the f-k filter. Both methods use a difference of an apparent horizontal velocity between a direct wave and a reflection from a target, and work automatically from position information of a transmitting antenna and a receiving antenna. One method is to mask an f-k spectrum in a region where a spectrum of the direct wave is distributed. The region is defined from the maximum and the minimum apparent horizontal velocity of the direct wave, which are calculated from the location of the transmitting antenna and the scanning area of the receiver. As for the other method, the most essential point is applying a time shift to eliminate a difference of an arrival time of a direct wave, where the time shift is calculated beforehand from the location of the transmitting antenna and the receiving antenna. Then, an apparent horizontal velocity of the direct wave becomes infinitely large due to the time shift. Thus, the f-k spectrum of the direct wave concentrates around a frequency axis because its slope is infinitely large. Then, a filter to reject the dc component in the spatial frequency direction is applied. Both methods are applied to an experimental data set which is acquired by a bistatic radar measurement to detect a buried landmine model with a depth of 10 cm. In addition, it is confirmed that they can suppress the undesired fluctuation of the images nearly one-tenth and help the reliable detection of a buried object. [ABSTRACT FROM AUTHOR]

In this paper, the polarization orientation angle shifts induced by artificial structures were analyzed and attempted to combine target orientation information which characterizes an urban area with the polarization orientation angle information extracted by the circular-polarization method. In order to illustrate the characteristic of the polarization orientation angle shifts represented in an urban area, the X-band polarimetric synthetic aperture radar (SAR) datasets of Sendai City acquired by Pi-SAR were used. This paper is based on Kimura's idea that the variation of the polarization orientation angle shifts depends on the artificial structures, particularly for the target rotation angle. We found that the polarization orientation angle shift is also affected by the relative relationship between the target rotation angle and the flight direction. From these results, it is possible to estimate the target rotation angle via computation of the polarization orientation angle shift from polarimetric SAR data. [ABSTRACT FROM AUTHOR]

We have investigated the impact of polarity of gate bias and Hf concentration on HfSiON/SiO2 gate dielectric breakdown (DB) with time-zero DB (TZDB) and time-dependent DB (TDDB). At TZDB, the gate leakage currents at breakdown (BD) under negative bias are much smaller than those with positive bias without regard to accumulation or inversion states. Since the electric fields at BD are not all the same, the BD mechanism cannot be explained with a simple thermochemical model for all types of stress for HfSiON gate dielectric. With TDDB, the electric-field acceleration constant is dependent on the Hf concentration. Calculated active dipole moments in HfSiON have been shown to be similar to theoretical values for nMOS but not pMOS. Thermochemic BD of HfSiON, itself (not interface SiO2), is adequate to describe nMOS in the inversion state. On the other hand, the BD of pMOS in the inversion state is affected by the carrier currents and not the electric fields as the TZDB. The BD mechanisms are strongly dependent on both the polarity of the gate bias and the Hf concentration. [ABSTRACT FROM AUTHOR]

A directional borehole radar system has been developed for the purpose of 3-D imaging of subsurface targets in a single-hole measurement. The radar system is equipped with a uniform circular array consisting of four dipole antennas as a receiver in order to realize azimuth bearing sensitivity. We propose a new direction-finding (DF) algorithm that is suitable for directional borehole radar measurement, and we apply this algorithm to actual field measurement data. This algorithm is based on the Adcock DF antenna principle where the complex time series (analytic signal) expression, the optimization, and the filtering procedure are incorporated to provide more accurate estimation. The algorithm was first verified in a transmission measurement in boreholes with a cross-hole configuration (15 m apart from each other) by estimating a direction of the incident wave from a transmitter to the receiver. Finally, the algorithm was applied to single-hole measurement data to demonstrate the ability to detect the 3-D location of a subsurface tunnel which was located 5.5 m from the borehole. The result showed fairly good agreement with the actual location of the tunnel, i.e., to an azimuth estimation error of within 10°. [ABSTRACT FROM AUTHOR]

A directional borehole radar system using an array antenna connected to passive optical electric field sensors was developed and evaluated by laboratory and field experiments. This system uses a single dipole antenna for a transmitter and a four dipole element circular array for a receiver. The received signals are transmitted through optical fibers from optical electric field sensors. The receiver array measures the phase differences between four dipole antennas and estimates the azimuth direction of the incoming reflection wave. The accuracy of the phase measurement was first evaluated in a laboratory test and then tested in a field experiment. To compensate for the sensitivity differences among the sensors, we propose an in situ calibration technique. The dominant operating frequency of the system is 70 MHz. Subsequently, we used borehole radar for subsurface measurements in a vertical borehole in granite. Estimation of the azimuth orientations of subsurface fractures was successfully demonstrated. [ABSTRACT FROM AUTHOR]

This paper discusses the reconstruction of the subsurface from radar data using a time-domain reconstruction method. Before the reconstruction is conducted, data preprocessing is carried out. The preprocessing transforms measured data transmitted and received by 3-D dipole antennas into equivalent data excited and received by 3-D ideal electric dipoles and, then, into equivalent data excited and received by 2.D ideal electric dipoles. Distributions of permittivity, conductivity, and permeability are reconstructed from the preprocessed data by a 2-D forward-backward time-stepping waveform inverse scattering technique. Two 2-D examples of permittivity and conductivity reconstruction from synthetic noisy and field borehole radar data are demonstrated to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A fully polarimetric borehole radar system using four combinations of dipole and slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes. First, to implement radar polarimetry analysis, a processing scheme suitable for analyzing a single-hole reflection data set acquired by the system is presented. This processing consists of antenna-characteristic compensation, migration for image reconstruction, and time-frequency analysis for single-frequency data set construction. Two polarimetric target decomposition methods, namely: 1) Pauli decomposition and 2) eigenvector-based decomposition, are applied to characterize the scattering problem of the subsurface fractures. The Pauli decomposition method provided important radar polarimetry information of fractures, and the eigenvector-based decomposition method made a significant contribution to understanding the scattering mechanisms from different fractures with different properties. Furthermore, information about fracture classification can be obtained by analysis of the H-alpha distribution provided by eigenvector-based decomposition of local radar image regions. The potential of polarimetric target decomposition techniques to fracture characterization is shown, which, in turn, provides valuable information about water permeabilities of fractures in hydrogeological studies. [ABSTRACT FROM AUTHOR]

A new parametric inversion technique to locate cylindrical structures has been developed for borehole radar crosshole measurements. The technique calculates prediction errors, focusing on curve shapes of first-arrival times, and explicitly uses known parameters on a target. Two schemes to compare the measured first-arrival time curves with the calculated ones are proposed. One is by taking the errors between curve gradients of measured and calculated first-arrival times, and the other is by taking the cross correlation between calculated first-arrival times and measured data. The schemes do not need to select the true first-arrival times, which makes this inversion technique robust and easy to use. This technique is validated with synthetic data sets modeling a metallic pipe in homogeneous and heterogeneous medium models. By both models, the inversion technique is able to retrieve the exact location of the pipe, though it employs a rather simple forward model, which can be solved by only geometrical calculations. The technique is applied to measured data sets, and it successfully estimates a pipe location in good agreement with known information. The inversion is also used for an air-filled subsurface cavity with a very simplified forward model, which considers only Snell's law at the cavity-subsurface media interface. It is also able to locate the cavity at a similar location estimated by other conventional techniques. [ABSTRACT FROM AUTHOR]

The accuracy of a migration image of ground-penetrating radar (GPR) depends strongly on the accuracy of permittivity distribution determined from multioffset data. This paper proposes a migration velocity analysis method using a genetic algorithm (GA). The objective function is defined as the summation of normalized zero-delay cross correlation of all common-image point gathers. Under the assumptions that the media are blockwise and that the permittivity of each block can be expressed as a polynomial with limited terms, all coefficients of the permittivity function of each block, which maximize the objective function, are deter- mined by migration velocity analysis method with GA Prestack migration is performed by a reverse-time migration method based on Maxwell's equations solved by the finite-difference time-domain method with a perfectly matched layer absorbing boundary conditions. The migration velocity analysis method is applied to synthetic common-transmitter datasets to test the method. Then, the velocity analysis and prestack migration method are applied to field data. From the distribution of dielectric constant obtained from the field data, water content is derived, and the depth of a water aquifer is deduced from the water content distribution and a migration stack profile. [ABSTRACT FROM AUTHOR]

Travel time tomography uses direct waves of crosshole radar data. A great deal of information concerning the media is contained in later arrivals, such as reflections and diffractions. More reliable results can be obtained by incorporating both direct waves and later arrivals. In this paper, the combination of travel time tomography and migration is introduced. A smoothed velocity model obtained by travel time tomography is used as the basis of migration. Then, a reverse-time migration technique is applied to direct-wave-suppressed crosshole data. The result of tomography indicates that there is an abnormal area, and the result of migration gives a more accurate position of the abnormal area, which is a cavity. The real example shows that the cooperation of tomography and migration is an effective technique for subsurface-cavity imaging. The synthesis of all information, including parallel crosshole measurement and forward simulation, assists in the interpretation of the results of tomography and migration. [ABSTRACT FROM AUTHOR]

An electromagnetic logging technique based on borehole radar is introduced in this paper. The tool consists of one transmitter and two receivers, which can be used to cancel the effect of the antenna characteristics by taking the ratio of two receiver signals. Since receiver signals measured in the time domain can be converted into the frequency domain by Fourier transformation, the amplitude ratio and the phase difference between two receiver signals in a wide-frequency band are obtainable. The response of the tool to different formations is investigated, and the algorithm that converts the amplitude and the phase information to the conductivity and the relative permittivity of the surrounding medium is given by a three-dimensional finite-difference time domain. The effect of the borehole on measurement and the response of the tool to a formation interface are simulated and analyzed numerically. The validity of this technique is confirmed by experiment. This technique can be applied to detect physical properties, including the conductivity and the relative permittivity, of the surrounding medium and the locations of the fractures intersecting the borehole. [ABSTRACT FROM AUTHOR]

Crosshole borehole radar measurement is needed to compensate the antenna transfer functions in polarimetric single-hole radar measurement with combinations of a dipole antenna and a cylindrical conducting slot antenna. This paper presents a method to estimate the antenna transfer functions from the single-hole measurement alone. A small dipole model in a homogeneous medium is used to approximate the relationship between the direct coupling wave in the single-hole measurement and the direct wave in crosshole measurement (antenna transfer function). We show that the far field crosshole signal approximately has the same frequency dependency as the time derivative of the direct coupling signal measured via single-hole measurement. We experimentally demonstrate that the measured far field waveforms have good agreement with the time derivative of the measured direct coupling waveform for dipole–dipole and slot–slot arrangements with an antenna separation of 1.6 m. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 11–21, 2000 [ABSTRACT FROM AUTHOR]

Proposes a polarimetric approach to extract information of reflected waves that is masked by the transmitter-receiver directly coupled wave in a single-hole borehole radar measurement. Formulation of antenna transfer function; Polarimetric reflection enhancement in single-hole measurement; Application of the approach; Conclusion.

Describes the use of the multiple signal classification (MUSIC) algorithm in three-dimensional (3-D) estimation target positions in ground-penetrating radar (GPR). Factors that limit bandwidth; Signal processing method for estimating 3-D positions using the conformal array; Examples of target positioning with both computer simulation and experiments.

Presents a full-polarimetric radar system with combinations of dipole antennas and axial slot antennas, applied to subsurface fracture measurement. Determination of a scattering matrix; Experimental procedure; Antenna characteristics in borehole; Conclusions.

A borehole radar is one form of ground penetrating radar which can be used in deep boreholes. We have been developing a directional borehole radar system with a conformal array antenna on a conducting cylinder. In this paper, we propose a 2-D MUSIC algorithm for the circular array of a directional borehole radar, which can be used to estimate the 2-D source location in a plane containing the array. A decorrelation technique is employed and we derive an algorithm which can determine the locations of two coherent sources. Experimental results obtained with the borehole radar show that this algorithm can accurately estimate parameters with a circular array having a radius of 0.03 m, which is much less than the signal wavelength of 0.8 m. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(6): 69–77, 1997 [ABSTRACT FROM AUTHOR]

Unwanted electromagnetic waves radiated from equipment making use of electromagnetic energy create numerous societal problems. The prevention of these problems has been studied extensively. In this paper, a method for estimating the location of the unwanted electromagnetic waves is studied. Since it is difficult to make the antenna aperture large especially at low frequencies, a search for electromagnetic wave source via a synthetic aperture technique is proposed. In the estimated electromagnetic source distribution by this method, images similar to the antenna sidelobes appear. It is demonstrated by computer simulation that the images can be suppressed by use of the synthetic aperture method with subarrays or use of Mill's cross method. Discrepancies between the true source location and the estimated location have been found in regard to the synthetic aperture length and the geometrical relationship with respect to the aperture center. It has been found that the antenna configuration with the synthetic aperture length of 10 λ can estimate an electromagnetic wave source within 10 λ square with accuracy of less than 1/4 λ square. Therefore this method is sufficiently practical if the location of the source is restricted somewhat. [ABSTRACT FROM AUTHOR]

In this paper, we present a velocity analysis technique using ground-penetrating radar (GPR) data to estimate near-surface soil-water content affected by topography and solar radiation on a mountain peak, mountain mid-slope, and alluvial plain sites in a semi-arid climate area in central Asia. By making precise measurements of reflected EM wave velocity, the water content in the near-surface soil was determined. The GPR experiments at several frequencies were carried out in two sequential phases (comprising common-offset and multi-offset methods) to obtain the soil-water content and illustrate the subsurface structure. We then tried to determine the relationship between near-surface moisture content and permafrost thawing. Therefore, we used several different methods including time-domain reflectometry and a resistivity survey. We also confirmed via the GPR data that vegetation cover indicates soil-water content in the near-surface soil. The results evaluated in this study provide meaningful information about soil water as well as subsurface structures. The GPR data acquired at the survey sites indicated a large range of near-surface water content due to the topography of the survey lines. [ABSTRACT FROM AUTHOR]

Charged defects in a gate insulating oxide significantly degrade electric properties of the field-effect transistors. We report on our analysis of the effects of Mg incorporation into HfO2 upon reduction in the positive charges associated with oxygen vacancies VO+2. Our comprehensive study using first-principles calculations revealed that a Mg atom substituted for Hf is stable in charge negative MgHf-2 and strongly binds with VO+2, neutralizing the defect. This contributes to the suppressing of the electron traps at the defect site, improving the reliability of Hf-based gate oxides. [ABSTRACT FROM AUTHOR]

In this article, we focus on the detection of the interlayer debonding of the asphalt airport pavement by the ground-penetrating radar (GPR) system. Since the interlayer debonding usually occurs in the shallow region of the asphalt airport pavement (several centimeters), it is difficult to interpret the anomalies or the defects from the GPR signals composed of many waves under the boundary conditions. Moreover, the wavelength of the ordinary GPR system is over several centimeters. Therefore, the spatial resolution of the system is not accurate enough to consider the millimeter thickness of the debonding layer. To overcome these problems, we propose a new method based on evaluating the lateral wave behavior of common midpoint (CMP) gathers collected by a multiple static GPR system. The multistatic GPR system is a stepped frequency continuous wave (SFCW) radar system, which consists of eight transmitting and eight receiving bowtie antennas. The system operates in the frequency range from 50 MHz to 1.5 GHz. After the validation of the simulation, the results of the interlayer debonding detection were evaluated by a field experiment obtained at Tokyo International Airport. The proposed method can detect the debonding layers which are less than 1 mm. Also, it is shown that our proposed method has a high consistency with the conventional acoustic finding method in the field measurement. It provides an innovative and effective method for the interlayer debonding detection of a partially damaged airport asphalt pavement, which is difficult to be observed by the ordinary GPR signals. [ABSTRACT FROM AUTHOR]

A quick response to a large-scale natural disaster such as earthquake and tsunami is vital to mitigate further loss. Remote sensing, especially the spaceborne sensors, provides the possibility to monitor a very large scale area in a short time and with regular revisit circle. Damage ranges and damage levels of the destructed urban areas are extremely important information for rescue planning after an event. Rapid mapping of the urban damage levels with synthetic aperture radar (SAR) is still challenging. Compared with single-polarization SAR, fully polarimetric SAR (PolSAR) has a better potential to understand the urban damage from the viewpoint of scattering mechanism investigation. In radar polarimetry, the dominant double-bounce scattering mechanism in an urban area is primarily induced by the ground-wall structures and can reflect the changes of these structures. In this sense, urban damage level in terms of destroyed ground-wall structures can be indicated by the reduction of the dominant double-bounce scattering mechanism, which is the basis of this study. This work first establishes and validates the linear relationship between the urban damage level and the proposed polarimetric damage index using polarimetric model-based decomposition. Then, efforts are focused on the development of a rapid urban damage level mapping technique which mainly includes two steps of urban area extraction and polarimetric damage level estimation. The 3.11 East Japan earthquake and tsunami inducing great-scale destruction are adopted for study using L-band multitemporal spaceborne PolSAR data. Experimental studies demonstrate that the estimated damage levels are closely consistent to the ground-truth. The final urban damage level map for the full scene is generated thereafter. Results achieved in this study further validate the necessity of exploring fully polarimetric technique for damage assessment. [ABSTRACT FROM PUBLISHER]

Takamura, M.; Udo, K.; Sato, M., and Takahashi, K., 2016. Analysis of Coastal Erosion due to the 2011 Great East Japan Tsunami and Its Recovery Using Ground Penetrating Radar Data. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 477-481. Coconut Creek (Florida), ISSN 0749-0208. The 2011 Great East Japan Tsunami caused severe beach erosion along the Pacific coast. Eroded beaches began to recover rapidly after the tsunami, but the rate of beach recovery declined recently. We conducted a ground-penetrating radar (GPR) and borehole survey at Yamamoto Beach, which was eroded by the 2011 tsunami, to understand the tsunami recovery process using a new method that combines GPR, satellite images or aerial photographs, and tidal data. We compared reflective surfaces with geological layers observed using the GPR and borehole survey, respectively, to investigate the relationship between the recovery process data obtained from the proposed method and the actual underground structure. The result of the GPR survey at Yamamoto Beach suggests that the estimated profiles from April 4, 2011 to November 2012 maintain a gradient ranging 0.05-0.13 and that recovery speed decelerated with time after the tsunami. The sedimentary structure after November 2012 differs from the previous structure as a result of levee construction. Boundaries formed by a layer between the sand and the sand with gravel layers were observed and found to be nearly consistent with the GPR reflection planes. GPR results identified differences in the water content ratio between the layers owing to changes in grain size. Moreover, GPR reflections appear where layer boundaries are not observed. This also suggests that GPR is capable of recording differences in soil properties that cannot be identified visually. [ABSTRACT FROM AUTHOR]

SUMMARY Damages on the surfaces of concrete buildings can easily be detected by visual inspection and can be repaired. However, damages inside walls need nondestructive inspection techniques to be detected, located, and identified. There has been a great demand for such techniques particularly after the 3.11 Great East Japan Earthquake. Ground-based synthetic aperture radar (GB-SAR) is a technique that can be potentially used for inspection of concrete walls in a nondestructive and noncontacting manner. The paper reports a fundamental experiment with a polarimetric GB-SAR system to detect internal damage in a concrete specimen caused by horizontal loading simulating earthquakes. The results show that the system does not have enough resolution to visualize individual defects, and that the effect of steel rebars installed inside the concrete is so strong that it masks weak responses. However, polarimetric analysis demonstrated the capability to minimize the effect of rebars by rearranging polarization basis and to extract weak responses. In particular, internal damages could be detected by observing the volume scattering component in this experiment. [ABSTRACT FROM AUTHOR]

It has been brought to the attention of the publisher that an error appeared in the citation of the original Japanese publication of the above article. It should read as follows: Translated from Denshi Joho Tsushin Gakkai Ronbunshi Vol. 79-B-II. No. 9, September 1996, pp. 574–582. We apologize for any inconvenience this may have caused the authors. [ABSTRACT FROM AUTHOR]

This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric synthetic aperture radar (PolSAR) data interpretation. The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain. A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency, and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain. A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived to indicate specific states of the rotation property. The rotation relationships between the coherency and covariance matrices with linear and circular polarization bases are established. A look-up table for these parameters is provided, and their physical meanings are interpreted. These derived parameters directly link to the Huynen parameters. Therefore, the proposed theory has the ability to achieve a desired state of one Huynen parameter by rotating the polarimetric matrix at a designated rotation angle. This theory also generalizes both the classic polarization orientation angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term. The roll-invariant terms have also been summarized. Finally, multifrequency Pi-SAR and AIRSAR PolSAR data sets are used to demonstrate the derived parameters. One oscillation amplitude parameter has been verified to be especially suitable for characterization of oriented man-made targets. Two angle parameters are sensitive to the reflection symmetry condition and crop types. Therefore, a simple unsupervised classification scheme has been developed and demonstrated. Further utilization perspectives of the proposed theory have been discussed. [ABSTRACT FROM PUBLISHER]

Hand-held ground penetrating radar (GPR) systems have been widely applied to landmine detections during recent decades. The accuracy of an imaging result by migration for a hand-held GPR is strongly related to the accuracy of subsurface velocity distribution obtained from multi offset data. For shallow targets like landmines, the hyperbolas are usually not distinct in 2D slices and are masked by the surface reflections. In this article, we propose a 3D migration depth focus velocity analysis method for hand-held GPRs to estimate the background velocity of the subsurface. This method is performed based on the images generated by migrations. The objective function is defined as the proportion of the target on the depth slice containing the target. After migrating a GPR radargram with different velocities, the background velocity, which minimizes the objective function, can be determined by comparing the imaging results by migration using different velocities. To test the proposed method, we apply this procedure to experimental GPR data collected with an advanced landmine imaging system (ALIS) in the laboratory. Subsequently, the velocity of the background is obtained, 3D diffraction migration with the obtained velocity achieves subsurface imaging with high quality. The accurate position and depth of the target are obtained from the optimal migration image. [ABSTRACT FROM AUTHOR]

The full-polarimetric ground-penetrating radar (FP-GPR) can obtain the polarimetric attributes of targets and achieve more accurate identification compared with traditional GPRs. However, in most cases, the polarimetric signals collected by GPRs are not only from the targets but also from the ground surface. According to the classical Fresnel formulas, the polarized directions of the waves will change after transmissions due to the difference in the transmission coefficients between horizontally and vertically polarized waves. This effect, called induced field rotation (IFR), will interfere with the acquisition of polarimetric attributes and also exists in the field measurements on a rough surface. In this study, we have derived the association between the measured FP-GPR data and transmission coefficients of the rough surface provided by the small perturbation method (SPM). The effects of IFRs from the rough surface on H-Alpha decomposition are analyzed later. The results show that the parameters of the rough surface will affect the values of components in the scattering matrix, but will not change the matrix and H-Alpha decomposition result; the incident angle and relative permittivity play main roles; for the H-Alpha decomposition results of three typical targets, the flat and dihedral are little influenced by IFRs, but the cylinder is seriously affected; simultaneously, a template for discriminating whether the calibration for H-Alpha decomposition is necessary is established. Both numerical and experimental tests validate the conclusions. Finally, a novel application strategy of H-Alpha decomposition is proposed, which has taken IFR from the rough surface into considerations. [ABSTRACT FROM AUTHOR]

There have recently been analyses of lightning electromagnetic fields using the FDTD method. However, large-scale three-dimensional analyses of a real environment have not been considered, because the FDTD method has a huge computational cost in large-scale analysis. Thus, we have proposed a three-dimensional moving window FDTD (MW-FDTD) method with parallel computation. Our method has a lower computational cost than the conventional FDTD method and the original MW-FDTD method. In this paper, we study the computational performance of MW-FDTD parallel computation and large-scale three-dimensional analysis of lightning electromagnetic fields on a real terrain model using our MW-FDTD with parallel computation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(2): 20-27, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22368 [ABSTRACT FROM AUTHOR]

In this article, an atmospheric phase screen (APS) compensation algorithm for a near real-time ground-based interferometry synthetic aperture radar (GB-InSAR) over a mountainous area is investigated. A novel APS compensation scheme is proposed to compensate the fluctuated APS caused by a spatial 3-D inhomogeneous refractivity index distribution without any a priori knowledge of moving location. The proposed method simultaneously addresses to identify moving pixels by a criterion of absolute velocity estimated by the coherent pixels technique (CPT). The proposed method consists mainly of three steps: 1) the stratified APS compensation; 2) identification of moving pixel candidate; and 3) the residual APS [remained APS after 1)] compensation by Kriging interpolation. The steps mentioned above are iteratively applied in order to increase the accuracy of the whole process. In this framework, we develop the 2-D quadratic polynomial model of the refractivity index with respect to slant range and topographic height for modeling the stratified APS. Furthermore, a prediction of the residual APS is achieved by applying the intrinsic random function of order $k$ (IRF- $k$) Kriging interpolation, taking into account the nonstationarity of the residual APS. We evaluate the proposed method using zero-baseline GB-differential InSAR (GB-DInSAR) data over a mountainous area located in Minami-Aso, Kumamoto, Japan, through the near real-time post-landslide measurement campaign. [ABSTRACT FROM AUTHOR]

A foreword to the to the special issue of "IEEE Transactions on Geoscience and Remote Sensing" about subsurface sensing using ground-penetrating radar (GPR) is presented.

By exploiting the sparsity of the scene containing only a few moving targets, a high-resolution and real-time range-Doppler map generation algorithm for passive bistatic radar is proposed. The proposed algorithm divides the long integration time into multiple short batches, from which a few batches are randomly selected on the basis of compressive sensing theory. A one-dimensional cross correlation is performed for each selected batch to obtain the range-compressed profile. Mean-value subtraction is then performed to suppress the direct path interference and stationary target reflections. Finally, an extended orthogonal matching pursuit algorithm is proposed for the effective estimation of target Doppler frequency. Practical application of this novel algorithm is examined by the detection of airplanes and ships via two synchronized general-purpose software-defined radio receivers. The results show that the proposed algorithm can achieve an improved resolution and a reduced sidelobe level compared to the conventional algorithms. [ABSTRACT FROM AUTHOR]

In this paper, the applicability of ground-based synthetic aperture radar (GB-SAR) as an early warning system for landslide monitoring is discussed. The effectiveness of the differential interferometric SAR (DInSAR) technique used in GB-SAR depends strongly on the geography of the monitored location. Therefore, an assessment of the system compatibility to select the most appropriate remote monitoring method is essential prior to any hardware implementation. In the preliminary part of this study, a 3D model was created using a LiDAR survey, and proposed locations for GB-SAR installation were examined. A 3D simulation was carried out to estimate the illumination from each of the proposed GB-SAR locations. The proposed model increased the efficiency of the GB-SAR positioning by minimising installation cost and time. Hardware configuration parameters, such as platform height, maximum range, and the direction and view angle of the radar line of sight were estimated by considering the optimum reflected power and ground illumination. Unlike on flat terrain, deployment of GB-SAR in a mountainous area is challenging because of surface anomalies and continuous changes in meteorological parameters, such as atmospheric temperature, pressure and relative humidity. In this study, the experimental site was located 3 km from the Aso volcano, and the weather conditions in the Aso caldera became a critical factor in accurately estimating the interferometric phase. The presence of atmospheric artefacts also compromises the applicability of the classical DInSAR technique. Here, we minimised the atmospheric phase screen by estimating the optimum data acquisition interval from GB-SAR monitoring under extreme weather conditions. The developed methodologies were then used to design a new landslide early warning system that measures real-time displacement over an area of 1 km2 within 10 s of scanning. This fully automatic monitoring system updates every 15 min and presents displacement information in a 3D interface. The system we have developed has been deployed for continuous monitoring of the mountainous environment of a road reconstruction site in Minami-Aso, Kumamoto, Japan where a large-scale landslide was triggered following the Kumamoto earthquake in 2016. [ABSTRACT FROM AUTHOR]

This paper examines the capability of a multi-static ground penetrating radar (GPR) system 'Yakumo' to estimate a vertical profile of dielectric constants of stratified geological layers. Yakumo is equipped with eight transmitting and eight receiving antennas. By using Yakumo, we propose to obtain an eight-channel common mid-point (CMP) gather from the 64-channel multi-static radar dataset acquired at each point on the survey line. From each CMP gather, a vertical profile of interval velocities can be estimated by velocity spectrum analysis. By a laboratory sandbox experiment, we validate that the thickness of an 83 cm sand layer is estimated with an error of less than 4%. A field survey carried out on tsunami deposits demonstrates that our GPR method can provide the spatial distribution of layer velocities of the sedimentary structure and that the results are comparable with the geological logs at three points and a conventional common-offset GPR profile. Velocity analysis is applied to explore the capability of a multi-static ground penetrating radar (GPR) system to estimate a vertical profile of dielectric constants of stratified tsunami layers. Both laboratory and field experiments demonstrate that multi-static GPR can accurately delineate the layered geological structures. [ABSTRACT FROM AUTHOR]

Identification of delamination in pavement layers using ground penetrating radar (GPR) is still challenging due to its limited range resolution. This paper investigates the characteristics of the composite reflection from the air-filled delamination between pavement layers by time-frequency analysis. We firstly simulated GPR data from an asphalt pavement model with an embedded air gap of different thicknesses by the Green’s function method. Then we conducted a laboratory experiment on a delaminated asphalt pavement model. Both the numerical and laboratory experiment results demonstrate that both the peak instantaneous frequency and its amplitude are sensitive to the variation of the air gap thickness. When the thickness of the air gap is smaller than a quarter of the dominant wavelength, the peak instantaneous frequency of the composite reflection is higher than that of the normal interface reflection. We conclude that we can identify the delamination from the overall rise in the peak instantaneous frequency. [ABSTRACT FROM AUTHOR]

SUMMARY Analysis of lightning electromagnetic field using the finite-difference time-domain (FDTD) method has been studies in recent year. However, large-scale analysis on real environment has not been considered, because the FDTD method requires huge computational cost on large-scale analysis. We proposed a three-dimensional moving window FDTD (MW-FDTD) with parallel computation and applied to large-scale analysis of lightning electromagnetic field with a real numerical terrain model. In this paper, we have studied about large-scale analysis of lightning electromagnetic field with real urban models considering many buildings using our MW-FDTD with parallel computation. We have shown effects of observed electromagnetic field on urban model. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of debris estimation which is one of the most important initial challenges in the wake of a disaster like the Great East Japan Earthquake and Tsunami. Reasonable estimates of the debris have to be made available to decision makers as quickly as possible. Current approaches to obtain this information are far from being optimal as they usually rely on manual interpretation of optical imagery. We have developed a novel approach for the estimation of tsunami debris pile heights and volumes for improved emergency response. The method is based on a stereo-synthetic aperture radar (stereo-SAR) approach for very high-resolution polarimetric SAR. An advanced gradient-based optical-flow estimation technique is applied for optimal image coregistration of the low-coherence non-interferometric data resulting from the illumination from opposite directions and in different polarizations. By applying model based decomposition of the coherency matrix, only the odd bounce scattering contributions are used to optimize echo time computation. The method exclusively considers the relative height differences from the top of the piles to their base to achieve a very fine resolution in height estimation. To define the base, a reference point on non-debris-covered ground surface is located adjacent to the debris pile targets by exploiting the polarimetric scattering information. The proposed technique is validated using in situ data of real tsunami debris taken on a temporary debris management site in the tsunami affected area near Sendai city, Japan. The estimated height error is smaller than 0.6 m RMSE. The good quality of derived pile heights allows for a voxel-based estimation of debris volumes with a RMSE of 1099 m 3 . Advantages of the proposed method are fast computation time, and robust height and volume estimation of debris piles without the need for pre-event data or auxiliary information like DEM, topographic maps or GCPs. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar (GPR) has been studied for landmine detection and identification. Since this application employs higher frequencies as compared to conventional largescale GPR measurements, the GPR performance is greatly influenced by soil properties and their spatial heterogeneity. In order to study the influence of soil heterogeneity on GPR performance, three types of soil were investigated. From the soil heterogeneity, GPR clutter was modeled with the aim of assessing the difficulty encountered in successful GPR performance. A handheld dual-sensor system that combines a metal detector and GPR was tested in these three test soils, and its performance for identifying buried objects was evaluated. The GPR performance obtained from the test showed a clear correlation with the modeled GPR clutter. Hence, the present study illustrates that clutter plays a major role in the detection of small objects in heterogeneous soil by GPR. [ABSTRACT FROM PUBLISHER]

The objectives of this study were to detect coarse tree root and to estimate root biomass in the field by using an advanced 3D Ground Penetrating Radar (3D GPR) system. This study obtained full-resolution 3D imaging results of tree root system using 500 MHz and 800 MHz bow-tie antennas, respectively. The measurement site included two larch trees, and one of them was excavated after GPR measurements. In this paper, a searching algorithm, based on the continuity of pixel intensity along the root in 3D space, is proposed, and two coarse roots whose diameters are more than 5 cm were detected and delineated correctly. Based on the detection results and the measured root biomass, a linear regression model is proposed to estimate the total root biomass in different depth ranges, and the total error was less than 10%. Additionally, based on the detected root samples, a new index named "magnitude width" is proposed to estimate the root diameter that has good correlation with root diameter compared with other common GPR indexes. This index also provides direct measurement of the root diameter with 13%-16% error, providing reasonable and practical root diameter estimation especially in the field. [ABSTRACT FROM AUTHOR]

Orientation angle compensation was incorporated into model-based decomposition to cure overestimation of the volume scattering contribution for interpretation of polarimetric synthetic aperture radar (PolSAR) data. The compensation is based on rotating the coherency matrix to minimize the cross-polarization term. However, this processing cannot always guarantee that the double- and odd-bounce scattering components will be rotated back to zero orientation angle and left with zero cross-polarization power. As a result, built-up patches with large orientation angles may still suffer from the scattering mechanism ambiguity. In this paper, double- and odd-bounce scattering models were generalized to fit the cross-polarization and off-diagonal terms, by separating their independent orientation angles. A general decomposition framework is proposed that utilizes all elements of a coherency matrix. The residual minimization criterion is used for model inversion. All the model parameters are simultaneously obtained using a nonlinear least squares optimization technique. The manual intervention, branch conditions, and negative power issues are avoided. The performance and advantages of this approach are demonstrated and evaluated with spaceborne L-band ALOS/PALSAR and airborne X-band Pi-SAR PolSAR data sets. Comparison studies are also carried out and demonstrate that further improved decomposition performance is achieved by the proposed method, especially in oriented built-up areas. [ABSTRACT FROM PUBLISHER]

The overestimation of volume scattering power and the scattering mechanism ambiguity are still present in model-based decompositions even with the implementation of the deorientation processing. These effects are demonstrated and investigated. One possible reason is because of the limited dynamic range of the models themselves that are not fully satisfied for the mixed scene cases. An empirical volume scattering model is proposed, using the repeat-pass polarimetric synthetic aperture radar interferometry (PolInSAR) coherence, to extend the model dynamic range to be more adaptive. PolInSAR coherence is sensitive to different types of forests and terrains. The proposed model inherits these characteristics. In addition, it considers the cross-polarization power induced by oriented man-made structures. Thereby, a model-based polarimetric decomposition scheme is developed. The efficiency of the proposed method is demonstrated using E-SAR airborne and ALOS/PALSAR spaceborne repeat-pass PolInSAR datasets. Comparative experiments are carried out and show that the proposed decomposition overcomes the scattering mechanism ambiguity between forests and oriented built-up areas, since it successfully identifies the oriented buildings as double- or odd-bounce man-made structures while keeping the volume scattering dominant for the forests. Besides, the stable decomposition performance over the oriented built-up patches with quite different orientation angles also validates the improvement of the proposed decomposition. In addition, the demonstrations with short and long temporal baselines validate the generality of the proposed method. [ABSTRACT FROM PUBLISHER]

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