Utility-Locating Technology Development Using Multisensor Platforms (2014) / Chapter Skim
Currently Skimming:
Pages 12-89
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 12... ...
12 C h a p t e r 3 Multichannel Gpr System Status, Findings, and applications UIT's strategy for part of this project was to build on the multichannel ground-penetrating radar (GPR) system, Terra Vision II, already constructed for enhanced utility detection.
|
From page 13... ...
13 manipulate GPR data for analysis. Other enhancements to SPADE include functions for 3-D migration of GPR data and automated target recognition routines.
|
From page 14... ...
14 GPR and potentially to seismic data. The system requires an optimal combination of machine and human intelligence.
|
From page 15... ...
15 neighbors than the width of the impulse response, which were assumed to be residual noise. This algorithm method was termed correlation peaks.
|
From page 16... ...
16 Figure 3.3a. Step 1 of four in peak joining.
|
From page 17... ...
17 Performance and Refinement of the Segmentation Method Segments offer clear identification of features in data, providing a global view of each structure in a 3-D interface. This can simplify the task of identifying pipe reflections, soil layers, and point objects by providing a more intuitive picture of the signal.
|
From page 18... ...
18 (to the swath) pipes; and longitudinal pipes (in the same direction as the swath)
|
From page 19... ...
19 which makes the algorithm relatively fast. The Kirchoff algorithm is a reverse time migration in which the raw image represents energy collected at the surface as a function of time, and this is propagated backward to find the distribution of energy in the ground at time zero.
|
From page 20... ...
20 For images which show polarization effects, splitting the polarizations would be expected to increase the performance of the migration process, by removing channels with negligible response to maximize the signal in the mapped hyperbolic sheet. Sagentia used a three-step process to split channels: (1)
|
From page 21... ...
21 Knowledge of seismic wave propagation in near-surface soil materials is critical to the design and optimization of an effective seismic method for detecting and mapping underground utilities. Because of regional variability in soils and localized variations in utility backfills, in situ field measurements are essential to gaining a full understanding of underground utility environments for realistic high-resolution seismic system performance.
|
From page 22... ...
22 demand close attention to devising proper field procedures. Thus, proven equipment technology capable of assuring acquisition of high-quality field data was used.
|
From page 23... ...
23 were made in preparing and configuring both the software and hardware components of the seismic data acquisition system for a full dry-run soil properties testing procedure. During this trial testing, in Traverse City, Michigan, the team determined the proper procedures for equipment setup, data acquisition, and initial data processing.
|
From page 24... ...
24 Figure 3.13. Ground coupler base late for MicroVib.
|
From page 25... ...
25 is, the software did not allow for synchronized generation of the toneburst excitation signal and the initiation of A-to-D sampling of the accelerometer signals. After some time, Dewetron software engineers were able to generate revisions to the software which allowed the synchronized seismic measurements to be made.
|
From page 26... ...
26 of the field data acquired in all of the test boreholes was relatively low because of apparent spurious response effects in the measurement apparatus, variations in coupling of the seismic vibrator source and sensor probes at the ground surface and downhole, and possible anomalous propagation effects and seismic reflection interference from subsurface soil layering. These factors produced amplitude and phase variations in the recorded seismic waveforms, making both velocity and attenuation analyses difficult, or impossible.
|
From page 27... ...
27 amplitudes must be free of any differing anomalous variations at the two measurement locations, and the measurements must be made at several frequencies to provide sufficient data for evaluating the frequency-dependent attenuation coefficient. The vibrator excitation signal used in these measurements was designed to generate toneburst signals having equal amplitudes and bandwidths to facilitate the measurements.
|
From page 28... ...
28 Figure 3.16. Downhole-detected signals at Houston borehole.
|
From page 29... ...
29 (introducing a possible cycle-skip error)
|
From page 30... ...
30 The higher velocities in Borehole F2 indicate a change in the soil seismic properties, characterized by an increase in shear modulus, at depths below about 10 ft. The uniform increase in slant-path S-wave velocity below 9 ft in Borehole E1 is indicative of a uniform soil exhibiting only the effects of soil column compaction.
|
From page 32... ...
32 Figure 3.21. Mean slant-path P-wave velocity, Houston Boreholes D2, E1, and F2.
|
From page 34... ...
34 Sufficient data obtained at depths to 9 ft in Borehole D2 and deeper in Boreholes E1 and F2 allowed reasonable determination of the effective Q values of soils at the three locations. The calculated values for Boreholes D2 and E1 are shown to illustrate the variations in the data.
|
From page 36... ...
36 Soil Seismic Properties Collective Results The soil seismic properties measurements were a qualified success in determining S-wave and P-wave velocities and attenuation rates at the three regional field sites. These results are considered to be representative of the seismic parameters of interest and are empirically estimated to have an accuracy tolerance of approximately 10% to 15%.
|
From page 37... ...
37 Irregular system responses at 1,100 Hz and lower caused amplitude and phase variations that introduced errors in the derived propagation velocity and attenuation. Unconventional analysis methods were devised and adapted to minimize these errors, with trade-offs between obtaining approximate values of S-wave and P-wave velocity and Q and their depth trends in the tested soils and not obtaining any useful information from the data.
|
From page 38... ...
38 positive velocity gradient versus depth. The features indicated in the cross section were divided into categories used to formulate the two-way transmission-reflection loss based on (1)
|
From page 39... ...
39 Figure 3.31. Pipe reflection cross section in near-surface soil medium.
|
From page 40... ...
40 depths for the different size pipes are indicated by extending the slopes of the curves down to the practical threshold limit (dashed lines)
|
From page 41... ...
41 depths for the different size pipes are indicated by extending the slopes of the curves down to the practical threshold limit (dashed lines)
|
From page 42... ...
42 Seismic Source Evaluation A major issue in evaluating the soil testing data was that many data sets contained data that didn't meet quality criteria for processing and computing of the desired parameters. With further study, the project team determined that many of the data sets were experiencing nonlinear results because larger than necessary signals were being generated by the microvibrator source.
|
From page 43... ...
43 Reprinted by permission, ASA, CSSA, SSSA. Table 3.1.
|
From page 44... ...
44 because of the increase of wave attenuation with the increase in wave frequency, the selected frequency range was as low as possible, as long as it satisfied imposed requirements on the resolution. WPP Modeling -- Attenuation To calculate the attenuation of the waves in the material instead of the attenuation coefficients, the WPP code uses the Q factors of the material.
|
From page 45... ...
45 of provided parameters used in the simulation is shown in Figures 3.24 through 3.26. WPP Modeling -- Computational Requirements The factors contributing to the computational requirements (RAM and number of CPUs)
|
From page 46... ...
46 chosen points under or on the ground. The unipolar case was represented by the shear pulse excitation in the form of the very smooth bump along the x-axis on the surface of the ground.
|
From page 47... ...
47 Figure 3.41. The propagation and reflection of the z-component of the unipolar shear pulse displacement in the x–z plane.
|
From page 48... ...
48 Figure 3.42. Values of the x-component of the unipolar S-wave displacement for each time step, at positions of 25 (top)
|
From page 49... ...
49 Figure 3.44. The shape of the vibrator pulse as input to WPP.
|
From page 50... ...
50 Figure 3.45. The propagation of the simulated pulse in the x–z plane.
|
From page 51... ...
51 Figure 3.46. Time series of the strength of the x-component of displacement at depths of, from top to bottom, 50, 100, 150, and 200 cm, showing the signal attenuation (the source was at a depth of 6 cm)
|
From page 52... ...
52 Figure 3.47. Values of the 200-Hz toneburst's amplitudes at different depths (normalized to the amplitude at the source, in agreement with the predicted 1/r attenuation)
|
From page 53... ...
53 Figure 3.49. Values of the 200-Hz toneburst's amplitudes at different depths, MicroVib source (normalized to the amplitude at the source compared with the geometrical 1/r attenuation; the source of the wave was the soft-soil Owen vibrator)
|
From page 54... ...
54 Figure 3.51. The propagation, in x–z plane, of the x-component of the 800-Hz toneburst.
|
From page 55... ...
55 Figure 3.53 and the accompanying animation show that the reflected signal is clearly visible. They also show that the strength of the reflected signal is on the order of the magnitude of physical and numerical background.
|
From page 56... ...
56 2 m under the ground is estimated to be ~77 dB. The simulation for a 1-ft-diameter plastic pipe 2 m under the ground showed that the total attenuation was ~87 dB.
|
From page 57... ...
57 Figure 3.39. The amplitude of the displacement and the time of arrival of the reflected pulse were recorded at those positions through the entire simulation run.
|
From page 58... ...
58 receivers define different hyperboloids, and the point of their intersection defines the position of the target. Verification of TDOA Method Many simulations were performed to demonstrate the adequacy of the TDOA method.
|
From page 59... ...
59 Figure 3.56. The propagation through the soil and reflection from the plastic pipe of the x-component of the shear pulse.
|
From page 60... ...
60 Figure 3.57. The propagation through the soil and reflection from the plastic pipe of the z-component of the shear pulse.
|
From page 61... ...
61 5-by-5 array in the first prototype, and (2) by asking the developer to build a custom 5-by-1 array for integration for the SHRP 2 R01B EMI prototype.
|
From page 62... ...
62 The system arrangement is shown in Figure 3.61. Equipment needed to run the system included the following: a.
|
From page 63... ...
63 Figure 3.62. Screenshots of EM3D data acquisition software.
|
From page 64... ...
64 receive signals for this sphere's data. The top plot shows the monostatic responses (same transmit-receive coil directly under sphere)
|
From page 65... ...
65 Figure 3.65. Current normalized and background-subtracted receive signals for 2-in.
|
From page 66... ...
66 earlier than 0.100 ms (from millivolts to volts in amplitude)
|
From page 67... ...
67 These tests indicated that the system was performing comparably to the original NRL TEMTADS 5-by-5 EMI array. SAIC sent a representative to assist UIT in the setup of the sensor platform and to conduct basic training on the R01B TDEMI system prototype.
|
From page 68... ...
68 while the pulse is off can only go out to 0.025 s. As one changes BlockT and nRepeats, one gets different pulse on/off times, which limits how late the time gates can go.
|
From page 69... ...
69 Figure 3.70. Measured data rate for single transmitter fired (red)
|
From page 70... ...
70 Figure 3.71. TDEMI measurements with 1-in.-diameter pipe 30 cm below sensor array.
|
From page 71... ...
71 Figure 3.72. TDEMI measurements with 1-in.-diameter pipe 60 cm below sensor array.
|
From page 72... ...
72 Figure 3.74. TDEMI prototype dynamic field test design.
|
From page 73... ...
73 range. At a gate width of 30%, there would be 16 time gates.
|
From page 74... ...
74 Figure 3.75. Plot showing the average/background-subtracted array time-decay response as a function of time gate(s)
|
From page 75... ...
75 Figure 3.77. Plot summing the array response of the three objects (by row)
|
From page 76... ...
76 e. To map the data, only new GNSS updates were kept.
|
From page 77... ...
77 ii. From top to bottom, the chains are spaced at 0-ft, 1-ft, and 2-ft apart.
|
From page 78... ...
78 iii. Speeds were varied from less than 0.5 m/s up to roughly 1.5 m/s.
|
From page 79... ...
79 The second involved viewing the data on a sensor-by-sensor basis. Each line of the Geosoft database represents a specific sensor, and the channels of each sensor line represent the exact numerical values for each point of the transmit-decay arrays.
|
From page 80... ...
80 functions and offered feedback to developers on a continual basis. Figure 3.84 illustrates the graphical user interface from this tool development of data import to a geophysical analysis software package.
|
From page 81... ...
81 is performed within the EM3D environment and is typically conducted at the end of a production day. This action results in the generation of two distinct files for each data set collected: the actual numerical data file (shown in Figure 3.85)
|
From page 82... ...
82 Figure 3.85. Sample raw excerpt (one data point)
|
From page 83... ...
83 Figure 3.87. Screenshot of Oasis Montaj profile view of monostatic channel for Sensor 1 (colored profile)
|
From page 84... ...
84 technology first spawned by SAIC and NRL's 5-by-5 TDEMI sensor array. The construction and development of the R01B prototype was incremental, as several first efforts were thwarted due to resource constraints and unforeseeable hardware malfunctions early in the project.
|
From page 85... ...
85 were not an issue with the units used for munitions classification because those systems collect data in static mode. Only during the past few years has the TDEMI system's fabricator learned to improve the hardware (and controlling software)
|
From page 86... ...
86 Highway (US-50) and moved south along the production route to specific areas representative of diverse underground utility conditions as determined by the project team, DOT, and SUE firm.
|
From page 87... ...
87 Figure 3.93. Establishment of survey control before geophysical investigations during in-service testing.
|
From page 88... ...
88 geophysicist reviewed all of the data sets with regard to data quality, coverage, and validity of the target selections. All the field notes, processing logs, and quality control (QC)
|
From page 89... ...
89 Table 3.8. So-Deep QL-B Versus R01B Tool Utility Footage -- Talbotton Road, Georgia Utility Results (Anspach and Skahn 2014)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.