David L. Wright

University of Florida

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Co-Authors

David V. Smith

WSP (Canada)

Misac N. Nabighian

Colorado School of Mines

Craig W. Moulton

United States Geological Survey

Theodore H. Asch

Framework

Yaoguo Li

Colorado School of Mines

Jerry A. Bradley

United States Geological Survey

Sudeep S. Sidhu

University of Florida

Miles Dyck

University of Alberta

Kraig L. Roozeboom

Kansas State University

Gregg R. Sanford

University of Wisconsin–Madison

Cooperative Institutions

Utah State University

Oregon State University

Louisiana State University

United States Geological Survey

Dale Bumpers Small Farms Research Center

Agricultural Research Service

Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias

Iowa State University

Center for Agricultural Resources Research

Kansas State University

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Microprocessor-Based Data-Acquisition System for a Borehole Radar

IEEE Transactions on Geoscience and Remote Sensing (1987)

Jerry A. Bradley David L. Wright

An efficient microprocessor-based system has been implemented that permits real-time acquisition, stacking, and digital recording of data generated by a borehole radar system. Although the system digitizes, stacks, and records independently of a computer, it is interfaced to a desktop computer for program control over system parameters such as sampling interval, number of samples, number of times the data are stacked prior to recording on nine-track tape, and for graphics display of the digitized data. The data can be transferred to the desktop computer during recording, or played back from a tape at a later time. Using the desktop computer, the operator can observe results while recording data and generate hard-copy graphics in the field. Thus, the radar operator can immediately evaluate the quality of data being obtained, modify system parameters, study the radar logs before leaving the field, and re-run borehole logs if necessary. The system has proven to be reliable in the field and has increased productivity both in the field and in the laboratory.

Microprocessor

10.1109/tgrs.1987.289855

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Citations (19)

Three-dimensional imaging of buried objects in very lossy earth by inversion of VETEM data

IEEE Transactions on Geoscience and Remote Sensing (2003)

Tie Jun Cui Alaeddin Aydiner Weng Cho Chew David L. Wright David V. Smith

The very early time electromagnetic system (VETEM) is an efficient tool for the detection of buried objects in very lossy earth, which allows a deeper penetration depth compared to the ground-penetrating radar. In this paper, the inversion of VETEM data is investigated using three-dimensional (3-D) inverse scattering techniques, where multiple frequencies are applied in the frequency range from 0-5 MHz. For small and moderately sized problems, the Born approximation and/or the Born iterative method have been used with the aid of the singular value decomposition and/or the conjugate gradient method in solving the linearized integral equations. For large-scale problems, a localized 3-D inversion method based on the Born approximation has been proposed for the inversion of VETEM data over a large measurement domain. Ways to process and to calibrate the experimental VETEM data are discussed to capture the real physics of buried objects. Reconstruction examples using synthesized VETEM data and real-world VETEM data are given to test the validity and efficiency of the proposed approach.

Born approximation

Lossy compression

Ground-Penetrating Radar

Synthetic data

10.1109/tgrs.2003.815974

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Citations (59)

Systems for Measuring Thickness of Temperate and Polar Ice from the Ground or from the Air

Journal of Glaciology (1981)

Raymond D. Watts David L. Wright

Abstract Equipment has been designed and tested for ground-based and airborne sounding of temperate glaciers. The transmitter is a free-running pulse generator that uses avalanche-mode transistor breakdown to create high-voltage pulses. The transmit and receive antennas are resistively loaded dipoles; for the airborne system, a twin-lead transmit element and a three-layer coaxial receive element are used on the inboard end of the respective antennas. The sounders are broadband systems; oscilloscopes are used for receivers. The oscilloscope trace is recorded photographically in the ground-based systems. A sampling oscilloscope is used in the airborne system—the sampling process strobes the waveform to audio frequencies so that it can be recorded on magnetic tape. Echoes have been obtained from ice depths of 550 m using the airborne system and about 1 000 m using the ground-based system.

Coaxial cable

10.3189/s0022143000011485

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Citations (21)

Determination of the Surface and Bed Topography in Central Greenland

Journal of Glaciology (1990)

Steven M. Hodge David L. Wright Jerry A. Bradley R. W. Jacobel Neils Skou

Abstract The surface and bottom topography of the central Greenland ice sheet was determined from airborne ice-radar soundings over a 180 km by 180 km grid centered on the 1974 “Summit” site (lat. 72°18′N., long. 37°55′W.), using the Technical University of Denmark 60 MHz ice radar. Over 6100 km of high-quality radar data were obtained, covering over 99'% of the grid, along lines spaced 12.5 km apart in both north-south and east-west directions. Aircraft location was done with an inertial navigation system (INS) and a pressure altimeter, with control provided by periodically flying over a known point at the center of the grid. The ice radar was used to determine ice thickness; the surface topography was determined independently using height-above-terrain measurements from the aircraft’s radar altimeter. The calculated surface topography is accurate to about ±6 m, with this error arising mostly from radar-altimeter errors. The ice thickness and bottom topography are accurate to about ±50 m, with this error dominated by the horizontal navigation uncertainties due to INS drift; this error increases to about ±125 m in areas of rough bottom relief (about 12% of the grid). The highest point on Greenland is at lat. 72°34′ N., long. 37°38′W., at an altitude of 3233 ± 6 m a.s.l. The ice surface at this point divides into three sectors, one facing north, one east-south-east, and one west-south-west, with each having a roughly uniform slope. The ice divide between the last two sectors is a well-defined ridge running almost due south. The ice is about 3025 m thick at the summit. Excluding the mountainous north-east corner of the grid, where the ice locally reaches a thickness of about 3470 m and the bed dips to about 370 m below sea-level, the maximum ice thickness, approximately 3375 m, occurs about 97 km south-south-west of the summit. The average bed altitude over the entire grid is 180 m and the average ice thickness is 2975 ± 235 m. The ice in most of the south-west quadrant of the grid is over 3200 m thick, and overlies a relatively smooth, flat basin with altitudes mostly below sea-level. There is no predominant direction to the basal topography over most of the grid; it appears to be undulating, rolling terrain with no obvious ridge/valley structure. The summit of the ice sheet is above the eastern end of a relatively large, smooth, flat plateau, about 10–15 km wide and extending about 50 km to the west. If the basal topography were the sole criterion, then a site somewhere on this plateau or in the south-west basin would be suitable for the drilling of a new deep ice core.

Greenland ice sheet

10.3189/s0022143000005505

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Citations (9)

New Field and Modeling Results from a Simulated Waste Pit Using The Enhanced Very Early Time Electromagnetic (VETEM) Prototype System

Symposium on the Application of Geophysics to Engineering and Environmental Problems 2000 (1999)

David L. Wright David V. Smith Jared D. Abraham Richard T. Smith Tie Jun Cui

PreviousNext No AccessSymposium on the Application of Geophysics to Engineering and Environmental Problems 1999New Field and Modeling Results from a Simulated Waste Pit Using The Enhanced Very Early Time Electromagnetic (VETEM) Prototype SystemAuthors: David L. WrightDavid V. SmithJared D. AbrahamRichard T. SmithTie Jun CuiWeng Cho ChewDavid L. WrightU.S. Geological Survey, MS 973, Box 25046, Federal Center, Denver, CO 80225‐0046, David V. SmithU.S. Geological Survey, MS 973, Box 25046, Federal Center, Denver, CO 80225‐0046, Jared D. AbrahamU.S. Geological Survey, MS 973, Box 25046, Federal Center, Denver, CO 80225‐0046, Richard T. SmithU.S. Geological Survey, MS 973, Box 25046, Federal Center, Denver, CO 80225‐0046, Tie Jun CuiDepartment of Electrical and Computer Engineering, University of Illinois, 1406 W. Green Street, Urbana, Illinois 61801‐2991, and Weng Cho ChewDepartment of Electrical and Computer Engineering, University of Illinois, 1406 W. Green Street, Urbana, Illinois 61801‐2991https://doi.org/10.4133/1.2922681 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Introductory paragraph for this paper is available only in the PDF and GZipped PS filesPermalink: https://doi.org/10.4133/1.2922681FiguresReferencesRelatedDetailsCited byDetection of buried targets using a new enhanced very early time electromagnetic (VETEM) prototype systemIEEE Transactions on Geoscience and Remote Sensing, Vol. 39, No. 12Novel diffraction tomographic algorithm for imaging two-dimensional targets buried under a lossy EarthIEEE Transactions on Geoscience and Remote Sensing, Vol. 38, No. 4Numerical modeling of an enhanced very early time electromagnetic (VETEM) prototype systemIEEE Antennas and Propagation Magazine, Vol. 42, No. 2 Symposium on the Application of Geophysics to Engineering and Environmental Problems 1999ISSN (online):1554-8015Copyright: 1999 Pages: 997 publication data© 1999 Copyright © 1999 The Environmental and Engineering Geophysical SocietyPublisher:Environmental & Engineering Geophysical Society HistoryPublished Online: 30 Sep 2008 CITATION INFORMATION David L. Wright, David V. Smith, Jared D. Abraham, Richard T. Smith, Tie Jun Cui, and Weng Cho Chew, (1999), "New Field and Modeling Results from a Simulated Waste Pit Using The Enhanced Very Early Time Electromagnetic (VETEM) Prototype System," Symposium on the Application of Geophysics to Engineering and Environmental Problems Proceedings : 811-820. https://doi.org/10.4133/1.2922681 Plain-Language Summary PDF DownloadLoading ...

Electromagnetics

10.4133/1.2922681

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Citations (3)

Interpretation of High-Resolution Low-Altitude Helicopter Magnetometer Surveys Over Sites Contaminated with Unexploded Ordnance

ASEG Extended Abstracts (2007)

Stephen Billings David L. Wright

SummaryThrough-out the world, millions of acres of potentially productive land are contaminated with unexploded ordnance due to either past-conflicts or to military training. Low-level helicopter magnetometry (HeliMag) is currently being used to rapidly cover large areas and identify regions that are potentially clear of hazardous munitions. The configuration we currently use comprises seven cesium vapour magnetometers, horizontally spaced 1.5 meters apart on a boom several meters in front-of a Bell 206L helicopter. Magnetometer data are collected at 400 Hz at altitudes as low as 1.5 m above the ground along transects spaced 7 meters apart. From this dense, high-resolution data, potential metallic targets as small as an 81 mm mortar are identified using manual and/or automatic picking methods. The target picks are then used to estimate densities of potential contamination. 100% detection is generally not feasible, so that HeliMag is usually applied in a characterization rather than in a clearance mode. We describe a HeliMag survey collected over a UXO contaminated site at Yekau Lake, near Edmonton, Canada. The objective was to identify the location and extent of an 11.5 pound bomb target area. The target density estimates derived from manual picks were strongly influenced by geology and clutter and did not reflect the underlying density of ordnance and ordnance related clutter. By fitting a dipole model to each target pick, and comparing it to the expected response of the target item, we could estimate the density of objects with similar size/shape to an 11.5 pound bomb. This analysis clearly identified an area of elevated contamination in the same region where 11.5 pound bombs were found during ground reconnaissance. In summary, the new methodology significantly improves the interpretability of HeliMag data when used for UXO site assessment.

Unexploded ordnance

Sonic boom

10.1071/aseg2007ab014

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Citations (1)

Alltem Uxo Detection Sensitivity And Inversions For Target Parameters From Yuma Proving Ground Test Data

15th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems (2007)

David L. Wright Craig W. Moulton Theodore H. Asch Philip J. Brown Misac N. Nabighian

ALLTEM is a multi-axis electromagnetic induction system designed for unexploded ordnance (UXO) applications. It uses a continuous triangle-wave excitation and thus measures target step<br>response rather than the more common impulse response. In May, 2006, we operated ALLTEM over the Army’s UXO Calibration Grid and Blind Test Grid at the Yuma Proving Ground (YPG), Arizona. The system multiplexed through all three orthogonal (Hx, Hy, and Hz axes) transmitting loops and recorded a total of 19 different transmitting (Tx) and receiving (Rx) loop combinations. This was accomplished while in continuous motion with a spatial data sampling interval, after waveform averaging, of 15 cm to 20 cm. ALLTEM records data at a constant 100 kilosamples/s rate at 24-bit precision rather than in a small number of time gates. Maps produced from differences between early- and late-time unfiltered signal amplitudes are of<br>high quality, but exhibit ground response and system thermal drift effects. We find that by exploiting the high density of the time-series data to digitally filter the data and by moving the early- time pick to 275 μs, late enough that the step response of an analog low-pass filter has settled, instead of the 75 μs early time we had previously used, we can produce amplitude difference data and maps that are almost free of ground response and system drift effects while retaining good sensitivity to UXO. The improvement in the signal-to-noise ratio (SNR) greatly enhances the ability to detect small or deep targets and also produces more consistent inversion results from ALLTEM data. An inversion algorithm has been developed and applied to data from various sets of the available 19 Tx-Rx combinations over a number of targets. We present results that show that the inversion algorithm produces accurate parameters for some known targets in the Calibration Grid. This suggests that it is possible to obtain good multi-axis system target inversions from moving platform data even with some position “noise.”

Unexploded ordnance

SIGNAL (programming language)

Impulse response

10.3997/2214-4609-pdb.179.01422-1435

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Citations (9)

Selecting soil hydraulic properties as indicators of soil health: Measurement response to management and site characteristics

Soil Science Society of America Journal (2022)

Dianna K. Bagnall Cristine L.S. Morgan G. Mac Bean Daniel Liptzin Shannon B. Cappellazzi

Abstract Farmers, scientists, and other soil health stakeholders require interpretable indicators of soil hydraulic function. Determining which indicators to use has been difficult because of measurement disconformity, spatial and temporal variability, recently established treatments, and the effect of site characteristics on management practice differences. The North American Project to Evaluate Soil Health Measurements includes 124 sites uniformly sampled across a range of soil health management practices in North America in 2019. We compare and recommend indicators of hydraulic function that best characterize soil health. We assessed the relationship of each indicator to a suite of soil inherent properties and climate variables, the response of each indicator to soil health management practices, the effect that soil inherent properties (clay content, sand content, and pH) and climatic variables (10‐yr mean annual precipitation and temperature) had on response to management practices, and the relationship among the responses of the indicators to soil health management practices. Field capacity measured on intact cores (θ FC_INTACT ) was the best measure of soil hydraulic function, because it responded to management, represents a direct measure of soil hydraulic function, is proximal to stakeholder values, and its response to management was not significantly influenced by inherent and climatic variables. Other suitable indicators are bulk density, soil organic carbon (SOC), and aggregate stability, which are not direct measures of soil hydraulic function but do respond to management and may be practical in situations in which measuring θ FC_INTACT is not. This study informs selection of soil health indicators to measure soil hydraulic function.

Pedotransfer function

Soil carbon

Soil Management

10.1002/saj2.20428

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Citations (30)

Improving GPR Image Resolution in Lossy Ground Using Dispersive Migration

IEEE Transactions on Geoscience and Remote Sensing (2007)

Charles P. Oden Michael H. Powers David L. Wright Gary R. Olhoeft

As a compact wave packet travels through a dispersive medium, it becomes dilated and distorted. As a result, ground-penetrating radar (GPR) surveys over conductive and/or lossy soils often result in poor image resolution. A dispersive migration method is presented that combines an inverse dispersion filter with frequency-domain migration. The method requires a fully characterized GPR system including the antenna response, which is a function of the local soil properties for ground-coupled antennas. The GPR system response spectrum is used to stabilize the inverse dispersion filter. Dispersive migration restores attenuated spectral components when the signal-to-noise ratio is adequate. Applying the algorithm to simulated data shows that the improved spatial resolution is significant when data are acquired with a GPR system having 120 dB or more of dynamic range, and when the medium has a loss tangent of 0.3 or more. Results also show that dispersive migration provides no significant advantage over conventional migration when the loss tangent is less than 0.3, or when using a GPR system with a small dynamic range.

Ground-Penetrating Radar

Lossy compression

Inverse filter

10.1109/tgrs.2006.888933

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Citations (22)

Instruments and Methods: A Digital Low-Frequency, Surface-Profiling Ice-Radar System

Journal of Glaciology (1990)

David L. Wright Steven M. Hodge Jerry A. Bradley Thomas P. Grover R. W. Jacobel

Abstract A new short-pulse digital profiling radar system that operates at lower frequencies than most ice radars used in polar regions to date has been designed and built by the U.S. Geological Survey. The transmitter is an avalanche transistor pulser which drives a resistively loaded dipole transmitting antenna. A similar, but separate antenna is connected to the receiver. The receiver has adjustable sensitivity time control (STC) of as much as 60 dB to compensate for attenuation and geometric spreading factors. A fiber-optic cable is used to transmit both control signals and data. The data-acquisition and display system incorporates very high-speed digitizing and signal averaging, real-time profile display, and data storage on standard computer nine-track magnetic tape. The system was successfully used on Ice Stream B in West Antarctica at centre frequencies of 1, 2, 4, 8, and 12.5 MHz. Bottom-return signal-to-noise ratios of more than 40 dB were obtained at 2 MHz through 800 m of ice. Convoluted internal surfaces not related to present bottom topography were resolved within the ice streams and anomalous strong reflections or “bright spots” were identified near the base of the ice. At present, there is no satisfactory glaciological explanation for either of these observations.

10.3189/s0022143000005633

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Citations (21)