Analysis of GPR data: wave propagation velocity determination

Tillard, Sylvie; Dubois, Jean

doi:10.1016/0926-9851(95)90031-4

Cited by 96 publications

(32 citation statements)

References 4 publications

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“…As expected, the deviation of parameters and properties estimated from pairs of measurements on a given day by and large fall well within the a posteriori 95% confidence limit for independent data sets. Thus, while we endorse the recommendation of Tillard and Dubois (1995) to employ repeat CMP measurements as a check on quality control, we note that a posteriori estimates of confidence limits from individual CMPs might provide an acceptable alternative for many applications. Regardless of the field procedure selected, in order to assure the proper assessment of data quality, we strongly emphasize the need to clearly state one's confidence limits, and define the basis for their estimation.…”

Section: Discussionmentioning

confidence: 86%

“…One set of procedures employs what we refer to here as internal checks in which information is used from only a single radargram, usually a CMP. The second set of procedures involves external checks using information from two or more independent radargrams from the same site on the same day (as recommended by Tillard and Dubois, 1995), or from the same site on different days.…”

Section: Discussionmentioning

confidence: 99%

“…Huisman and Bouten (2003) report an observed reproducibility (standard deviation) to 4 significant figures of ±0.2411 ns for traveltimes in a study employing 450 MHz center frequency antennas and a sampling interval of 0.06 ns. Tillard and Dubois (1995) used semblance analysis (or velocity scans) to interpret GPR data collected using 50 MHz, 100 MHz, and a 200 MHz center frequency antennas, and they estimate the uncertainty in their analysis to be ±0.002 to ±0.005 m/ns. Greaves et al (1996) used 100 MHz center frequency antennas and state that their precision is ±0.012 m/ns or 8%, measured by the width of the central semblance maximum.…”

Section: Introductionmentioning

confidence: 99%

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Assessing the Precision of GPR Velocity and Vertical Two-way Travel Time Estimates

Jacob

Hermance

2004

JEEG

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Accurate estimates of ground penetrating radar (GPR) traveltimes and velocities are essential to a number of civil engineering, agricultural and watershed management activities. This paper reports on a study to assess confidence limits on radar parameters using a sequence of high quality common midpoint (CMP) soundings collected on eight different days over the course of a year at a single location for a range of soil moisture conditions. On each day, a "repeat" CMP was acquired leading to a total of 16 independent CMP soundings.Two prominent reflections, present in all 16 independent CMP soundings, were analyzed to provide NMO velocities and vertical two-way traveltimes along with their associated 95% confidence limits estimated using Student's t-test, accounting for both the appropriate number of observations and estimated parameters. Interval properties were then determined using the Dix relation. The radar velocity of the 1 st interval has the largest variation observed, from 0.074 (±0.002) m/ns to 0.146 (±0.003) m/ns for wet and dry soil moisture conditions, respectively. However, over this same time period, the estimated thickness of each interval, 0.9 (±0.1) m and 2.9 (±0.2) m, remains constant within the respective 95% confidence limits on the 16 independent estimates and their composite average. The latter result provides a useful check on the quality of our interpretation. Analysis of the ground refraction phases also confirmed the interval velocity and thickness inferred from the reflection data.The global results of this study suggest that NMO radar velocities and vertical two-way traveltimes may be optimally resolved at the 95% confidence level with precisions of ±0.001 m/ns and ±0.7 ns, respectively. The deviation between measurements from repeat CMPs on a given day typically fall well within the 95% confidence limit. Thus, while repeat CMP data provide a valuable check on quality control, we note that a posteriori estimates of confidence limits might provide an acceptable alternative for many applications. Regardless of the field procedure selected, this study emphasizes that an assessment of data quality is only possible by a clear statement of confidence limits and by carefully defining the basis for their estimation.

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Assessing the Precision of GPR Velocity and Vertical Two-way Travel Time Estimates

Jacob

Hermance

2004

JEEG

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“…The ground wave velocity was determined at a first approximation from the distance/travel time diagram. The propagation velocities at greater depths were determined from velocity scans (semblance analysis) of the CMP data (Tillard & Dubois 1995) using the REFLEXW program. Jacob & Hermance (2004) report a typical accuracy of c. +0.01 m ns 21 .…”

Section: Ground-penetrating Radar (Gpr)mentioning

confidence: 99%

The formation of Alpine lateral moraines inferred from sedimentology and radar reflection patterns: a case study from Gornergletscher, Switzerland

Lukas

Sass

2011

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Studies on the formation of alpine lateral moraines are rare; consequently, their internal structure and their modes of formation are relatively poorly understood. We present here sedimentological and ground-penetrating radar (GPR) data from a lateral moraine complex where an exposure allows radar facies to be compared to the field evidence. The moraine, which is slightly asymmetric with a slightly steeper distal slope, consists of alternating clast-and matrix-supported stratified diamicts and intercalated sorted sediment units which are all subparallel to the moraine surface. They are interpreted as subaerial debris flows and fluvial sediments, respectively. The GPR, using frequencies of 50, 100 and 200 MHz, allows tracing of very similar subparallel reflectors to c. 10 m into the subsurface. These are interpreted to represent the diamict units while the thickness of the sorted sediment units is below GPR resolution. Our data suggests that a two or three frequency approach supplemented by common-midpoint (CMP) measurements works well in glaciated high-mountain environments. Based on our sedimentological and GPR data we develop a conceptual framework for the formation of successive lateral moraines which involves ice-contact fan sedimentation, followed by collapse and incremental reworking of the proximal side during glacier retreat.

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“…One such approach is the use of ground penetrating radar (GPR), which can provide a much improved record of subsurface stratigraphy and can be successfully utilized in both sandy dological framework for GPR investigations of fluvial sediments that builds upon past research (e.g. Daniels et al 1988; Davis & Annan 1989;Peters et al 1994;Jol 1995;Tillard & Dubois 1995;Young & Sun 1999). By drawing attention to these methodological issues, it is anticipated that the quality of future GPR studies can be improved in order to aid both interpretation and comparison between datasets.…”

mentioning

confidence: 99%

The use and application of GPR in sandy fluvial environments: methodological considerations

Woodward

Ashworth

Best

et al. 2003

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Ground penetrating radar (GPR) is a popular technique for imaging and interpreting sedimentary architecture. However, current literature shows a wide range in the quality of information provided on the GPR methodology and processing technique. It is therefore difficult to judge the validity of the GPR interpretations and this produces inherent difficulties for comparison between surveys. This paper describes the key steps required to collect, process and interpret GPR surveys in sandy fluvial sediments. GPR data from the South Saskatchewan River, Canada, are used to illustrate each stage of data collection and processing. Particular attention is given to the appropriate set-up conditions for the GPR software and hardware, the selection of dataprocessing techniques and velocity analysis. Methods for the interpretation of GPR reflectors are also investigated using ground-truth control provided by a cut-face exposure. This paper presents recommendations for a systematic and rigorous methodology for the collection, processing and interpretation of GPR data in sandy fluvial environments. The paper suggests that all data-collection parameters and processing steps should be recorded or tabulated in any GPR publication to facilitate comparisons between surveys.deposits (e.g. Bridge et al.

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Analysis of GPR data: wave propagation velocity determination

Cited by 96 publications

References 4 publications

Assessing the Precision of GPR Velocity and Vertical Two-way Travel Time Estimates

Assessing the Precision of GPR Velocity and Vertical Two-way Travel Time Estimates

The formation of Alpine lateral moraines inferred from sedimentology and radar reflection patterns: a case study from Gornergletscher, Switzerland

The use and application of GPR in sandy fluvial environments: methodological considerations

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