radar de penetración terrestre una breve descripción y estudio de casos . ingles

7/27/2019 Radar de penetracin terrestre una breve descripcin y estudio de casos . INGLES

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Ground penetrating radar: a brief overview and case study

Harry M . Jo l and Derald G . Sm ith

Ground penetrating radar (GPR) is a recently evolving technique for detailedsubsurface investigation of sedim entary environm ents. Field experim ents at over a 100sites have been conducted over the last year and half. These tests have provided insightsinto many areas of Western Canada and United States. The resulting profiles provide highresolution, continuous subsurface data on facies thickness and depths. The application ofradar stratigraphic analysis (distinct reflection signature patterns) on the collected dataprovides both lateral and vertical geom etry and stratification of sand bodies underinvestigation. Interpretations derived from the radar data coupled w ith other non-GPR data(i.e. seism ic, borehole data) w ill aid in understanding the complex nature of depositionalenvironm ents and provide useful analogues for com parison w ith ancient depositionalsystems.

Ground penetrating radar w as used on the m odern lacustrine William River delta,northem Saskatchewan, to better understand the subsurface sedim entology and reconstructform er depositional processes (Figure 1). Radar profiling of the w ave-influenced sanddeposits along transects up to 3.2 km in length provided high resolution continuoussubsurface data of facies thickness and depths, lithology contacts, dip angle and dipdirection of major sedimentary structures (Jol and Smith, in press ; Figures 2 and 3).

A pulseEKKO IV radar system was used w ith 50 and 100 MHz antennae at a onem etre step for all reflection surveys (Figure 4). Each step location w as stacked w ith asam pling rate of 800 ps. The profiles w ere processed and plotted (w iggle trace form at)using pulseEKKO IV softw are. N ear surface velocity m easurem ents w ere calculated from

CM P surveys (Figure 5). A review of GPR principles and case histories is provided byA nnan and Davis (1977), Beres and Haeni (1991), Davis and Annan (1986, 1988, 1989),Moorm an (1990), Morey (1974), and U lriksen (1982).

GPR has been found to be a very effective system in assessing subsurfacestratigraphy, depth of lithofacies boundaries and large scale sedim entary structures. Theresulting radar stratigraphy m odels could have considerable value to the explorationgeophysicists / geologists in the aggregate, placer mining, oil and gas industries. In ourexperience, GPR w as found to be m ost effective (resolution and depth of penetration) inquartzose, dry and /or wet (freshwater), clean (no clay), sandy and gravelly environments(Jol and Sm ith, in press). O ther subsurface data acquisition m ethods w ith sim ilar orcomparable resolution, continuity, portability, cost effectiveness and tim e efficiency do notexist when assessing the shallow subsurface (0 - 30 m). Given these conditions, GPR is

unm atched by any other m ethodology in earth sciences.


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References

Annan, A .P. a nd D avis, J.L., 1977, Impulse radar applied to ice thickness mea sur emen ts and freshwaterbathymetry: Geological Survey of C anada, Report of Activities, P aper 77-1B.

B eres, M ilan, Jr. and H aeni, F.P., 1991 , application of grotm d-penetrating-radar m ethods in hydrogelogic

stu dies: G ro un dwater, 2 9, n o. 3 ,37 5-38 6.Davi s, J.L. and Annan , A.P., 1986, High resolutio n sounding using grou nd probing radar: Geoscience

Can ad a, 1 3, n o. 3 ,2 05 -2 08 ., 1988, Application s of the pulseEKKO III g r ound penetrating radar system to mining,

ground water and geo technical p ro jects - selected c ase hist ories: Worksho p on Gro und P robingRadar, Ottawa, On tar io, May 24-26., 1989, Ground-penetrating rada r for high-resolution mapping of soil and ro ck stratigraphy:

Geophysical Prospecting, 37, 531-551.Jol, H.M. and Smith, D.G., in press, Ground penetrating radar of northern lacust r ine deltas: Canadian

Journ al of Earth Sciences .

Moorman, B.J., 1990, Assessing the ability of ground penetrating radar to delinea te subsurface fluviallithofacies: M.Sc. thesis, University of Calgary.

Morey, R.M., 1974, Detection of subsurface cavities by ground penetrating rada r : Highway GeologicalS ymposium , Proceedings 27, 28-30.

Ulriksen, C. P .F., 1982, Applica tion of impulse rada r to civil engineering: ph.D. thesis, Lu nd Universityof Technology.

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FIG. 1 . Location map of the s tudy areawhere GPR fie ld experiments were carried ou t ontheWilliam River delta (above location in Canada, below location of surveys on the de ltasurface).


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Distance (m)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 1 70 180

0 -

1O0 - - :_r ._'_ 5. 2 -

I, -

400 _15

t _ _"

600 - ,_ / c . , ,__ # ,_

FIG . 2. Radar profile of the m odern W illiam River D elta, northern S askatchew an. T he survey parallels the right bank ofthe William River (Figure 1).


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D is ta nc e (m )

0 10 20 30 40 50 60 70 80 90 100 110 120130

140 150 160 1

70

180,,i,+_,, .!. t . .. .. .. _, ._ ,_ , ,,t ,+ .... T 0

O+

t

IO0_T 5

200

_. tO=_ ._a

o_ 300 aE

15 "# '.0400 o

1

600 i

FIG . 3. Radar pr ofile of the m odern William River delta, n orthern Saskatchewan . The survey parallels the sh oreface ofth e d elta ( Fig ure 1 ).


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Direction of Survey

(a)

n 'dsurface

e . - .

Q_

D

Reflector

Source

instant"" o f airwave

Arrival o f directwave(groundwave)E

F -

c--_""_ > ''_< _'Arrival of

, re fle c te d wave

FIG. 4. Groun d penetrating radar profiling procedure. (a) The step-like pr ocedureinvolves repetitive moves of both the transm itter and receiver at a constat spacing. (b) Fiveschem aticGPR traces, show ing the arrival of airw ave and ground-w ave pulses and a low erreflected wave from a sub surface reflector.


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Receiver positions Transmitter positions

Steps

(a ) 7 6 5 4 3 2 1 1 2 3 4 5 6 7

ANTENNAE SEP ARAT ION (m)

(b) 5 10 15 20 25 30 35

0

lO 0

200 Air wave

300

_O

=_ 400IL l

500

600 "

Gro und wave700 _ dx (surface distance)

__ dt (two way t Tavel lime)00 38m

I = - 0107m lne

550ns

FIG. 5. (a) Common M id Point (CMP) technique used to determ ine the electrom agneticpropagation velcity of the surface sedim ents. (b) An example of a CM P profile used tocalculate the near-surface velocity of the William R iver delta, northern Sask atchewan.

radar de penetración terrestre una breve descripción y estudio de casos . ingles

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