VSP traveltime inversion: Near‐surface issues

Moret, Geoff J. M.; Clement, William P.; Knoll, Michael D.; Barrash, Warren

doi:10.1190/1.1707053

Cited by 23 publications

(17 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…7(b) is the virtual refraction. The virtual refraction has an average velocity v 1 = 2700 m/s, which agrees well with the P‐wave speed in saturated sand (Moret et al 2004). This is the identical moveout speed as the refraction speed in the real shot record.…”

Section: Surveysupporting

confidence: 70%

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡

Nichols

Mikesell

Wijk

2010

Geophysical Prospecting

View full text Add to dashboard Cite

A B S T R A C TSeismic interferometry is a relatively new technique to estimate the Green's function between receivers. Spurious energy, not part of the true Green's function, is produced because assumptions are commonly violated when applying seismic interferometry to field data. Instead of attempting to suppress all spurious energy, we show how spurious energy associated with refractions contains information about the subsurface in field data collected at the Boise Hydrogeophysical Research Site. By forming a virtual shot record we suppress uncorrelated noise and produce a virtual refraction that intercepts zero offset at zero time. These two features make the virtual refraction easy to pick, providing an estimate of refractor velocity. To obtain the physical parameters of the layer above the refractor we analyse the cross-correlation of wavefields recorded at two receivers for all sources. A stationary-phase point associated with the correlation between the reflected wave and refracted wave from the interface identifies the critical offset. By combining information from the virtual shot record, the correlation gather and the real shot record we determine the seismic velocities of the unsaturated and saturated sands, as well as the variable relative depth to the water-table. Finally, we discuss how this method can be extended to more complex geologic models.

show abstract

Section: Surveysupporting

confidence: 70%

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡

Nichols

Mikesell

Wijk

2010

Geophysical Prospecting

View full text Add to dashboard Cite

show abstract

“…[], for further information on well construction, and details about positive well skin). Stratigraphic units at the BHRS (Figure ) have been defined based initially on distributions of porosity estimated from neutron logs and grain‐size characteristics from core [ Barrash and Clemo , ; Reboulet and Barrash , ; Barrash and Reboulet , ], and similar structures have been recognized through analysis of ground‐penetrating radar (GPR) [ Clement et al ., ; Clement and Barrash , ; Clement and Knoll , ; Irving et al ., ; Ernst et al ., ; Bradford et al ., ; Dafflon et al ., ], seismic [ Moret et al ., ], and capacitive conductivity [ Mwenifumbo et al ., ] surveys.…”

Section: Field Site and Data Collectionmentioning

confidence: 99%

Hydraulic conductivity imaging from 3‐D transient hydraulic tomography at several pumping/observation densities

Cardiff

Barrash

Kitanidis

2013

Water Resources Research

Self Cite

104

123

View full text Add to dashboard Cite

[1] 3-D Hydraulic tomography (3-D HT) is a method for aquifer characterization whereby the 3-D spatial distribution of aquifer flow parameters (primarily hydraulic conductivity, K) is estimated by joint inversion of head change data from multiple partially penetrating pumping tests. While performance of 3-D HT has been studied extensively in numerical experiments, few field studies have demonstrated the real-world performance of 3-D HT.Here we report on a 3-D transient hydraulic tomography (3-D THT) field experiment at the Boise Hydrogeophysical Research Site which is different from prior approaches in that it represents a ''baseline'' analysis of 3-D THT performance using only a single arrangement of a central pumping well and five observation wells with nearly complete pumping and observation coverage at 1 m intervals. We jointly analyze all pumping tests using a geostatistical approach based on the quasi-linear estimator of Kitanidis (1995). We reanalyze the system after progressively removing pumping and/or observation intervals; significant progressive loss of information about heterogeneity is quantified as reduced variance of the K field overall, reduced correlation with slug test K estimates at wells, and reduced ability to accurately predict independent pumping tests. We verify that imaging accuracy is strongly improved by pumping and observational densities comparable to the aquifer heterogeneity geostatistical correlation lengths. Discrepancies between K profiles at wells, as obtained from HT and slug tests, are greatest at the tops and bottoms of wells where HT observation coverage was lacking.Citation: Cardiff, M., W. Barrash, and P. K. Kitanidis (2013), Hydraulic conductivity imaging from 3-D transient hydraulic tomography at several pumping/observation densities, Water Resour. Res., 49,[7311][7312][7313][7314][7315][7316][7317][7318][7319][7320][7321][7322][7323][7324][7325][7326]

show abstract

“…The regularized inversion that lies at the heart of Occam’s approach also allows for an independent estimation of data error based on the discrepancy principle (Hansen ; Moret et al ) that is purely based on the characteristics of the regularized slowness inversion. Hansen () found that a function

ν (λ)

can be defined as a combination of the elements of the regularized inversion objective function, where

λ

is the regularization parameter, i.e., the weight of the smoothness constraint with respect to the fit of the data.…”

Section: Methodology: Vertical Radar Profilesmentioning

confidence: 99%

Vertical radar profiling for the assessment of landfill capping effectiveness

Cassiani

Fusi

Susanni³

et al. 2008

Near Surface Geophysics

View full text Add to dashboard Cite

In this paper we present the results of the characterization of a large landfill cap by means of ground‐penetrating radar (GPR) measurements. The GPR data were collected in boreholes, using a vertical radar profile (VRP) configuration, where one antenna was kept at the ground surface while the other was progressively lowered into the borehole. This yields a vertical profile of GPR velocity from which a moisture content profile can be obtained. VRPs were conducted in 15 boreholes available on‐site, all having been drilled through the protective cap and the waste mass into the underlying native soil. The separation between the boreholes (many tens of metres) makes it infeasible to characterize the site via other forms of hole‐to‐hole GPR measurements, with the exception of a few pairs of holes drilled at the periphery of the waste mass and therefore of limited usefulness. The VRP data allowed for the characterization of the moisture content profile across the waste body down to the water table, very close to the natural land surface, providing evidence that the waste is generally fairly dry (moisture content less than 10% on average). In order to assess the effectiveness of the cap, two surveys where conducted in March and April 2005 using all the boreholes with the aim of identifying moisture content changes due to natural rainfall and especially artificial irrigation over a limited area surrounding one of the boreholes. The time‐lapse VRP results show that in the irrigated area a measurable amount of water seeps through the cap and changes the waste moisture content. Elsewhere, we basically observed no changes in moisture content due to natural infiltration during the same period: this fact does not confirm or exclude that some degree of leakage can occur. Direct in‐situ permeability measurements, albeit more localized than VRP data, confirm that the landfill cap is not totally impermeable, thus corroborating the results derived from geophysical measurements.

show abstract

VSP traveltime inversion: Near‐surface issues

Cited by 23 publications

References 23 publications

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡

Hydraulic conductivity imaging from 3‐D transient hydraulic tomography at several pumping/observation densities

Vertical radar profiling for the assessment of landfill capping effectiveness

Contact Info

Product

Resources

About

VSP traveltime inversion: Near‐surface issues

Cited by 23 publications

References 23 publications

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site‡

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site‡

Hydraulic conductivity imaging from 3‐D transient hydraulic tomography at several pumping/observation densities

Vertical radar profiling for the assessment of landfill capping effectiveness

Contact Info

Product

Resources

About

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡

Application of the virtual refraction to near‐surface characterization at the Boise Hydrogeophysical Research Site^‡