CRREL REPORT 95-24

Ground-Penetrating Radar

Investigation of the Proposed Dome–

CARA Tunnel Route and Utilities at

South Pole Station, Antarctica

Steven A. Arcone, Wayne Tobiasson

and Allan J. Delaney December 1995
For conversion of SI units to non-SI units of measurement consult Standard

Practice for Use of the International System of Units (SI), ASTM Standard E380-

93, published by the American Society for Testing and Materials, 1916 Race St.,

Philadelphia, Pa. 19103.

Cover: View of the dome and arches at South Pole Station, looking at the main

entrance.

Abstract

Ground-penetrating radar studies were performed at South Pole Station, Antarctica, during January 1993 to determine if subsurface obstructions exist

along a planned tunnel route from the main station to the new astrophysical

research area on the far side of the skiway, and if various man-made subsurface features such as sewage sumps, a water well, utilidors and buried buildings could be located and delineated. The maximum depth of interest for the

tunnel survey was approximately 10 m. For it, a short-pulse antenna transducer with its antenna bandwidth centered near 400 MHz was towed along

the ground surface over multiple traverses to cover an area up to 60 m wide.

The survey extended from the South Pole Station fuel arch,across the skiway

and then to the CARA site (Center for Astrophysical Research in Antarctica).

The radar profiles show reflections from density layering within the snow

caused by traffic and diffractions from artificial features within 13 m depth.

Debris is present in the snow west of the skiway and near the fuel bladder

near the taxiway. Targets within 100 m of the west side of the skiway are

extensive, and appear to be metallic. The tunnel should be routed in the clear

area north of them. Targets near the fuel bladder are only 3 to 4 m below the

surface. The tunnel could go under them, but as a precaution they could be

removed. An additional survey was run over a 30-m-wide swath from the

ASTRO facility at the CARA site to the new elevated dormitory, a distance of

approximately 800 m. This swath appears to be clear of any subsurface

debris, except very near the dormitory. Surveys per-formed at several utility

sites near the main station provided a general assess-ment of the dielectric

properties of the firn, and tested the radar’s ability to deline-ate subsurface

features and potential hazards. Migrated, spatial images of the old clean air

facility, the water well under development, and the several sewage sumps are

presented. In general, the numerous vents, cables, antennas, etc., of the area

clutter the profiles with diffractions that complicate interpretation of the data

without prior knowledge of some features. The migrated images allowed approximations to be made as to the depths of sewage sumps, the water well

and the old buried clean air facility.
CRREL Report 95-24

Ground-Penetrating Radar

Investigation of the Proposed Dome–

CARA Tunnel Route and Utilities at

South Pole Station, Antarctica

Steven A. Arcone, Wayne Tobiasson

and Allan J. Delaney December 1995

Prepared for

NATIONAL SCIENCE FOUNDATION

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Dr. Steven A. Arcone, Geophysicist, Snow and

Ice Division, Wayne Tobiasson, Research Civil Engineer, Civil and Geotechnical Engineering Research Division, and Allan J. Delaney, Physical Science

Technician, Snow and Ice Division, Research and Engineering Directorate,

U.S. Army Cold Regions Research and Engineering Laboratory. Funding for

this research was provided by the National Science Foundation under Grant

no. DPP-872 0063.

Technical review of this report was provided by Donald Garfield and John

Rand of CRREL.

The contents of this report are not to be used for advertising or promotional

purposes. Citation of brand names does not constitute an official endorsement

or approval of the use of such commercial products.

ii
iii

CONTENTS

Preface .................................................................................................................................... ii

Introduction ........................................................................................................................... 1

Radar equipment .................................................................................................................. 2

General operation ............................................................................................................ 2

Antennas ........................................................................................................................... 2

Antenna directivity ......................................................................................................... 2

Field procedures and data processing .............................................................................. 3

Field procedures .............................................................................................................. 3

Data recording, filtering and processing ..................................................................... 4

Results and discussion ........................................................................................................ 5

Station site surveys .......................................................................................................... 5

Proposed tunnel routes ................................................................................................... 17

Conclusions ........................................................................................................................... 22

Literature cited ...................................................................................................................... 23

Abstract .................................................................................................................................. 25

ILLUSTRATIONS

Figure

1. Short-pulse radar wavelet transmitted and received by 400-MHz GPR

antennas ................................................................................................................... 2

2. Radar transmit–receive two-way directivity pattern for a finite size dipole ...... 3

3. 400-MHz antenna transducer unit in tow behind a Spryte tracked vehicle ........ 4

4. Wiggle trace display of a series of scans and the equivalent line intensity

display ..................................................................................................................... 5

5. Layout of facilities and radar survey lines at South Pole Station, January 1993 6

6. 400-MHz profile of the metal utilidor tunnel ........................................................... 7

7. 400-MHz profile and its migration along line XZ that crosses the old clean air

facility ...................................................................................................................... 8

8. Wide angle reflection and refraction profile performed at about 400 MHz

near the OCAF ........................................................................................................ 9

9. 100-MHz time section profile across the water well ............................................... 10

10. Migration of the water well profile ............................................................................ 11

11. Two-dimensional depiction of the disposition of sewage within sump 1

at location A ............................................................................................................ 11

12. 400-MHz time-section profiles and their migrations .............................................. 12

13. Two versions of the 400-MHz profile recorded at 300 ns across line FG over

sump 2...................................................................................................................... 14

14. Migration of the central section of the sump 2 profile using a migration

velocity based on nm = 1.54 .................................................................................. 15

15. Three parallel 400-MHz profiles recorded at 200 ns at the far sump location .... 16

16. Migration of the profile along the centerline JK at the far sump .......................... 17

17. 400-MHz time-section profile from the center of the far sump back toward

the lift station .......................................................................................................... 18

18. Proposed tunnel routes ................................................................................................ 18

19. Profiles of lines D and G along section A of the tunnel survey ............................. 19

20. Segments of lines CC–J that contain the many diffractions west of the skiway . 20

21. Plan view of the primary tunnel survey ................................................................... 22

22. Plan view of the survey run between the ASTRO building and the elevated

dormitory ................................................................................................................ 23
INTRODUCTION

Currently, a new facility is being built at South

Pole Station, Antarctica, for infrared (IR) and

millimeter wave (MMW) observatories operated

by the Center for Astrophysical Research in Antarctica (CARA). This new research site is located

about 200 m west of the skiway. Sensitivity to IR

and MMW radiation is greatly enhanced by the

absence of atmospheric water vapor and by very

low telescope temperatures that reduce ambient

IR noise; consequently, winter operations are necessary. A tunnel has been proposed to connect the

CARA site with the main station. In it, personnel

could move safely between the two places, which

are about 1 km apart, even during the dark, cold

winter-over period. A machine has been built at

CRREL to excavate the tunnel, but the tunneler

may be damaged if it encounters a large metal or

wood object. Thus, the tunnel route must avoid

any debris that has ended up in the snow during

the 35 years that people have been present at the

South Pole.

Commonly, magnetometry and low-frequency

magnetic induction methods are used for metal

detection. However, the nonmetallic nature of

some of this debris, the 10-m depth of interest and

the need to locate the objects accurately makes

Ground-Penetrating Radar (GPR) the preferred

method.

The objectives of our GPR surveys were 1) to

locate any objects buried in the snow along the

proposed route of the tunnel, 2) to determine the

radar’s ability to delineate known objects associated with the buried facilities near the main station, and 3) to assess the possible hazard of sewage sumps to the new water well near the main

station. The surveys performed near the main station are discussed first, as they allowed establishment of the snow dielectric properties needed for

estimating the depth of the objects in the tunnel

route survey.

The tunnel route was surveyed using a GPR

antenna transducer, operating at 400-MHz pulse

center frequency, that was either pulled by hand

or towed by vehicle along closely spaced, parallel

transects covering a swath up to 60 m wide. The

buried facility surveys were done at 100- and 400-

MHz center frequencies. Some of the results were

used to determine snow dielectric properties,

which were needed to transform the GPR echo

time delays into depth scales. As of this writing,

there has been no drilling or excavation to verify

the features of interest on the GPR records. Verification would be valuable.

GPR has been a common geophysical tool for

subsurface exploration in snow and ice (e.g.,

Kovacs and Gow 1975, Kovacs et al. 1982, Arcone

and Delaney 1987, Arcone 1991) and frozen soils

(e.g., Annan and Davis 1976, Kovacs and Morey

1979, Delaney et al. 1991, Arcone 1992) because of

the ease at which radio waves penetrate these

materials. Commercially available, low-power,

low-gain GPR systems are able to penetrate several meters in fine-grained permafrost, tens of

meters in frozen sands and gravels, and well over

a hundred meters in polar snow and ice. Vertical

resolution is determined by the bandwidth center

frequency of the pulse used. For antennas operating near 500 MHz, resolution is generally about

24 cm in dense snow, 20 cm in ice and less for

dielectrically denser materials such as permafrost. This exceptional resolution has led GPR to

become a popular device for characterizing utiliGround-Penetrating Radar Investigations

of the Proposed Dome–CARA Tunnel Route and

Utilities at South Pole Station, Antarctica

STEVEN A. ARCONE, WAYNE TOBIASSON AND ALLAN J. DELANEY
ties and hazardous waste sites (e.g., Hanninen and

Autio 1992, Pilon 1992), as most structures, subsurface debris, water and fuel spills, or the soil disturbances they cause, are strong radar targets.

This report discusses the use of GPR to detect

such targets at South Pole Station, Antarctica. A

companion report (Arcone et al. 1994) discusses

additional surveys on the use of GPR in the vicinity of McMurdo Station, Antarctica.

RADAR EQUIPMENT

General operation

The radar utilized a Geophysical Survey Systems, Inc., SIR Model 4800 control unit, 100- and

400-MHz pulse center frequency antenna transducers, cables, a GSSI DT6000 digital tape recorder

and a power supply. The control unit keys the

transmitter on and off at 50 kHz (synchronized

with the receiver), sets the scan rate (rate at which

echo scans are compiled; generally 25.6 scans/s),

scan time range and the time range gain to be applied to the scans. The transmit antennas radiate a

broadband pulse lasting only a few nanoseconds

(ns) at 400 MHz and about 15–20 ns at 100 MHz.

Consequently, the antenna produces a low-gain

radiation directivity pattern in ice or firn. Pulse

shapes and directivity are discussed in detail below. A separate but identical receive antenna is

employed because echoes can return from nearsurface targets before the transmit antenna has

stopped radiating. The received signals are converted by sampling into an audio frequency facsimile for filtering, amplification, digitization and

recording.

Antennas

All antennas were flared and resistively loaded dipoles designed to produce a wavelet of

about 2 cycles duration (Fig. 1). All wavelets have

a 3-dB frequency bandwidth of about 35%. The

100- and 400-MHz characterizations refer to the

approximate instantaneous frequencies of the radiated wavelets when coupled to snow or ice;

higher frequencies result when radiating in air.

The 400-MHz transmitter and receiver antennas

are backshielded and housed in one unit (Model

3102, GSSI, Inc.) at a separation of about 15 cm.

The transmitter produces an 8-W peak power excitation. A 100-MHz pair of transmit and receive

antennas (Model 3207, GSSI, Inc.) was also used

and they are of the same design, but housed in

separate backshielded units so that the separation distance is variable.

Antenna directivity

The antenna beam pattern radiated into the

ground must be considered when planning a survey of parallel lines so that subsurface coverage

can be complete. Theoretical transmit radiation

Figure 1. Short-pulse radar wavelet transmitted and received by

400-MHz GPR antennas. The wavelet shape is similar for both 100-

and 400-MHz antennas. SOS is an artificial start-of-scan pulse and

DC is the direct coupling between antennas (followed by resonance attributable to the snow cover). The large amplitude subsurface reflection

is from a utilidor metal roof and the + – + – phase polarity sequence is

characteristic of a conductive, or positive (i.e., higher than overburden),

dielectric anomaly. The opposite sequence occurs for a negative

anomaly such as a void. Amplitude (linear scale)

DC Subsurface

Reflections

+

+

–

–

SOS

0 30 60 90 120 150

Time (ns)

2
3

 = 1.9


 = 0.5

ε


ρ

Snow, two-way


22-cm dipoles

180°

90°

49°

110°

H Plane

E Plane

 = 2.5


 = 0.7

ε


ρ

Snow, two-way


22-cm dipoles

180°

90°

44°

100°

E Plane

H Plane

 = 3.2


 = 0.92

ε


ρ

Ice, two-way


22-cm dipoles

180°

90°

43°

92°

H Plane

E Plane

Figure 2. Radar transmit–receive two-way directivity

pattern for a finite size dipole operating over snow of different densities ρ and their corresponding dielectric constants ε. The directivity is much greater in the E-Plane,

which is perpendicular to the direction of surveying. The 3-

dB angular width in the E-plane gives an approximate base

for calculating the antenna swath of sensitivity.

The effective transmit–receive directivities for

a theoretical model of our radar antennas (Arcone

1995) are shown in Figure 2. These patterns are

the far field radar response to a point target that is

isotropic, polarization insensitive, non-dispersive and located in three different media. The

dielectric constants ε of the media are 1.9, an

approximate value (e.g., Cumming 1952) for the

upper layer snow at South Pole Station, 2.7

(dense snow) and 3.2 (ice). The patterns are more

directive than those of a single antenna because

of the multiplication of the identical transmit and

receive directivity patterns. The patterns were

computed for an antenna length of 22 cm, excited

by a 2.5-ns (400-MHz) current pulse that progressively attenuates along the length of the antenna.

The patterns are similar for the virtually identical,

but larger, 100-MHz antennas.

The two-way directivity in the plane of the

electric field (E-plane, which is the vertical plane

containing the antenna and perpendicular to the

ground surface), shows a main lobe and two

weaker sidelobes. In snow of density 0.5 g/cm3,

the main lobe has a 3-dB beamwidth of 49° and

the sidelobes are 5 dB weaker than the main lobe

peak. Therefore, at a depth of about 5 m, the lateral coverage or “footprint” is determined by the

main lobe and is about 4.6 m wide. The line spacing for the tunnel route survey averaged 2.8 m so

that overlapping coverage was obtained. The unorthodox magnetic field plane (H-plane, which is

the vertical plane perpendicular to the E-plane

and the ground surface) pattern has two scalloped lobes whose peaks are about 9 dB above the

peak E-plane intensity. An effective H-plane

beamwidth is not simply characterized, but using

the peak values in the 40° direction as a reference,

the 3-dB width of each lobe is approximately 10°.

This causes signal intensity to vary strongly

along diffraction patterns generated when passing over discrete objects because profiling was

done along the H-plane direction. This variation

generates “noise” during migration. Migration is

a signal processing procedure used for resolving

diffractions to improve the spatial imaging of the

radar data. It is used later and discussed below.

FIELD PROCEDURES AND

DATA PROCESSING

Field procedures

We established transects over facilities near

South Pole Station by placing orange plywood

diamonds in the snow at set intervals along lines

patterns for point dipoles have been discussed by

Annan et al. (1975) and Engheta et al. (1982). This

theory shows the radiation to be directive with

deep nulls and sharp lobes in planes parallel and

perpendicular, respectively, to the antenna axis.

These features occur in the angular directions ψ =

± sin–1 (1/n) measured from vertical, where n is

the real part of the refractive index of the ground

medium. For solid ice, n = 1.78 and |ψ| = 34°.

This angle steadily increases to a value of 46.5° for

snow of n = 1.38 (density 0.5; Cumming 1952).
4

Figure 3. 400-MHz antenna transducer unit in tow behind a Spryte tracked

vehicle. The transducer contains the antennas and transmit and receive electronics.

No reflections from the Spryte were apparent in the records. Spryte speed was generally about 5 m/s. Also shown is the two-way radar antenna directivity patterns in firn,

both perpendicular (⊥) and parallel () to the profile line direction. The perpendicular

pattern covers a subsurface swath extending about ±25° to the sides of the antenna.

to be surveyed and then slowly dragging the antennas by hand from diamond to diamond.

Transects along the proposed tunnel route were

done by slowly dragging the antennas over the

surface behind a Spryte tracked vehicle (Fig. 3) at

8–13 km/hr (5–8 miles/hr) along similarly

marked lines. Differences in record length ascribable to changes in towing speed between diamonds or flagged bamboo poles were compensated for by computer processing. All surveys

were performed with the antennas polarized perpendicular to the transect direction so that the

stronger amplitude H-plane pattern was in the

line of the transect. The spacing of the tunnel lines

sometimes varied by a few meters to avoid surface obstacles. Thus, the exact position of targets

located is not known. Event markers were placed

electronically on the tunnel records at known positions along each traverse. The transect line spacing averaged 2.8 m, slightly more than the 2.5-m

width of the vehicle’s tracks.

Data recording, filtering and processing

All data were recorded in scans of either 512 or

1024 8-bit words for later processing by dedicated

software (Galinovsky and Levin 1990). Horizontal

(i.e., over distance or equivalently, many scans)

frequency filtering mitigated near-surface ringing

from the direct coupling between antennas, and

vertical (i.e., over time, or equivalently, along one

scan) filtering mitigated dc gain variations resulting from inconsistent antenna–ground coupling.

Data are displayed as consecutive scans in a distance-vs.-echo-time arrangement (known as a

“time section”) (Fig. 4) for which several schemes

for displaying signal amplitude are available.

Only selected sections of the tunnel survey will be

shown owing to the large amount of data.

Translation of echo time delay t from a target

into the depth d of the target is generally based on

the simple echo delay formula

d = ct/2n (1)
5

where d is measured in centimeters, t in nanoseconds and c is the speed of electromagnetic

waves in a vacuum (30 cm/ns). The quantity n is

often replaced by ε ; where ε = 3.2 for ice and

about 1.9–2.2 for most of the near-surface snow

encountered. The factor of two in eq 1 accounts

for the round trip propagation path of the pulse

and applies only to reflections from horizontal interfaces or to scattering from point sources. Equation 1 can be applied to several layers successively if n is known for each layer and the time delays

to each layer interface are easily picked from the

record.

Proper transformation of a standard radar distance-vs.-time profile into a more useful spatial

image of distance vs. depth is achieved by a computational process known as migration, commonly used in seismic data processing. Migration

is not necessary where reflecting horizons gradually change depth with distance, but should be

used where reflections strongly slope or curve

and may be masked by strong diffractions from

local targets.

Migration is achieved by many methods. The

most common, the Kirchhoff diffraction summation method (e.g., Yilmaz 1987), is used in these

studies. Migration requires a wave velocity (or

value of n) for each material type encountered,

but we used a one-layer approximation for the

snow; i.e, we assumed that the snow is a homogeneous matrix of constant n and containing embedded anomalies. In fact, n increases gradually

with depth. We used a migration refractive index

value, nm, calculated from matching the hyper0

10

20

30

40

50

Time (ns)

Distance

Figure 4. Wiggle trace display (left) of a series of scans received as the antenna

moves over a short distance, and the equivalent line intensity display.

bolic diffractions with a model hyperbola. The values obtained, calculated at an accuracy of about

±4%, produced good migrations, as judged by the

collapse of the diffraction hyperbolas to a small

area, and can therefore be considered as nearly the

average refractive index.

All time section profiles to be migrated had to

be compressed (i.e., stacked, wherein each scan is

replaced by the average of several scans symmetrically placed about it) so that an adequate migration aperture (number of scans processed at one

time) could be obtained to cover an entire diffraction. The resulting migration was then stretched

by interpolating between scans to give a reasonable ratio between depth and distance scales. Details of the migration algorithm and the probable

effects of antenna directivity upon it are discussed

in Arcone et al. (1995).

 Migration is used primarily in the studies of

the dome facilities to help us interpret subsurface

structure. The diffractions that emanated from the

many targets encountered along the proposed

tunnel route are not migrated because they themselves are evidence of target presence (their obscuration of snow layering is of no interest) and their

amplitude and waveforms may supply information about their material nature.

RESULTS AND DISCUSSION

Station site surveys

The objectives of these surveys were twofold: to

obtain values for the effective dielectric constant of

the firn (i.e., snow over a year old, but not yet com-
6

pressed into glacial ice) over various

depths, and to locate or delineate subsurface facilities and utilities, or both.

Figure 5 shows the general layout of

South Pole Station and the surveys. The

facilities discussed are the present water

well, several sewage sumps produced

over the years (indicated as sump 1,

sump 2 and far sump), a utilidor and the

buried Old Clean Air Facility (OCAF).

Each survey line is lettered (e.g., FG)

with the alphabetical order indicating

the direction of the line. Several

transects are indicated at each site, but

not all are presented in this report as

some did not traverse the features of interest. One Wide-Angle Reflection and

Refraction (WARR) line (transmitter and

receiver antenna offset constantly increased: on the diagram) was made near

the OCAF to evaluate the refractive index of the surface snow. Dielectric

information was gathered from all surveys. The weather during all profiles

was clear with light winds and temperatures between –13 and –26°C, which necessitated placing the radar control unit

within an insulated box.

Near the surface, snow density is approximately 0.35 g/cm3 and increases to

a firn density of about 0.8 by 100 m

depth (Bogorodsky et al. 1985). About 15–20 cm

of new snow accumulates each year at the South

Pole. The snow that was on the surface during the

beginning of the International Geophysical Year

(IGY; 1957) when the South Pole was first permanently occupied was about 4–5 m below the surface at the time of our surveys. Over the years objects have been buried. Some objects are even

deeper, since pits were dug to bury waste as far

back as the IGY. In the early 1970s, a second station was built 1.4 km from the original IGY station, creating heavy vehicular traffic between the

two stations. This created a hard, compacted layer that, at the time of our surveys, was 3 to 4 m

below the snow surface. That traffic area crosses

routes proposed for a tunnel and is evident in

many of the radar surveys. Extra snow accumulation around the main station places that layer 4 to

5 m deep there and it is also visible in the radar

records. However, since all snow above it has

since been compacted by annual snow control operations, other layers are also evident in the radar

survey.

Figure 5. Layout of facilities and radar survey lines (end points

alphabetically marked) at South Pole Station, January 1993. Line

marked WARR is a wide angle survey.

Also apparent in all the records are diffractions

unrelated to the feature of interest. We expect that

these “clutter” events are generated by buried

objects including trash, spills, vents, cables and

antennas.

Metal utilidor

The metal utilidor leading south from the main

station (Dome in Fig. 5) was first surveyed (line

DE) to establish a calibration value for the snow

velocity since the exact depth (5.65 m) from the

snow surface to the crown of the metal tunnel

was known. The utilidor tunnel itself is 2.0 m

high (Fig. 6). Figure 6 also shows the radar profile, acquired with the 400-MHz transducer. The

prominent but distorted hyperbolic diffraction

under the centerline symbol and whose apex is at

49-ns delay is the response to the utilidor roof.

The reflected wavelet at the apex is the large reflection shown in Figure 1. Several other hyperbolas appear in the profile and are generated by

buried objects whose depth and placement relative to the vertical plane of the survey line is not

Taxiway

Bladder

Fuel Hut

Garage

Arch

Generator

Arch

Biomed

Arch

Fuel

Arch

Z

S

V

T

R

Skylab

Dome Cargo

Arch

Balloon

Inflation

Water

Well

Q

P

0

B

Utilidor

Vent

0 50 100 150 200 m

I

K

M

L

J

H

C

F

G

Elevated

Sewer Line

WARR

Met.

Tower

Grid North

(Greenwich

Meridian)

Far Sump

U

W

OCAF

X

D

E

A Sump 1

Sump 2

N
7

known. The distortions in the diffractions are

caused by uneven towing speed. The more uniform left limb of the utilidor diffraction can be

matched with a theoretical curve generated with a

refractive index nm = 1.26 (ε = 1.57), which is close

to the values (1.30, 1.69) corresponding to the velocity arrived at using the utilidor depth and time

delay. These values correspond to snow density of

0.34–0.37 g/cm3 (Cumming 1952) and are slightly

less than other values obtained at the South Pole

and discussed below.

Old Clean Air Facility (OCAF)

This facility has been abandoned and is known

to be under several meters of snow; our purpose

here was to find it. A 100-m survey line (line XZ in

Fig. 5) that apparently traversed the roof is shown

in Figure 7, along with its migration. The data

were horizontally filtered and compressed sufficiently to allow the maximum migration aperture

(127 scans) permitted by the software to cover an

entire diffraction. All the diffractions fit a model

hyperbola generated by a migration velocity corFigure 6. 400-MHz profile of the metal

utilidor tunnel along line DE in Figure 5.

The distortions in the diffractions are

caused by uneven antenna towing speed.

The time delay to the utilidor roof and the

diffraction itself correspond to a dielectric

constant of 1.57 and a snow density of

about 0.34 g/cm3.
responding to an ε = 1.93, which corresponds to a

firn density of 0.5. The correctness of this value is

revealed in the migration, which transforms the

unmigrated data into several horizontal surfaces.

The unmigrated data of Figure 7 reveal a linear

coherent reflection at about 55 ns delay, and

many diffractions of which two, centered at 15

and 29 m, are very prominent. The migrated data

show the linear reflector to be between 17 and 28

m. We presume that a major part of the linear reflection is the roof at a depth of about 5.5 m. The

facts that 1) the 11-m distance is much greater

than the original roof dimensions (6.4 × 7.3 m;

diagonal length = 9.8 m) and, 2) that there are

many more diffractions originating at 60 ns towards point Z, suggest that there is more structure buried. The apexes of the prominent diffractions are at about 40 ns and the migrated data resolve these diffractions into two apparent columns. The strong diffraction originating at about

15 m collapses to a horizontal surface (i.e., coherent reflection) about 2 m wide at 4 m depth. The

diffraction at 29 m distance also collapses to a coherent reflection at about 4 m depth, but it is not

as linear. These diffractions could be responses to

metal pipes placed to mark the location of the

8

Figure 7. 400-MHz profile (top) and

its migration along line XZ that

crosses the old clean air facility.

Many of the diffractions in the top profile have collapsed into discrete events

in the migrated section. The linear reflector provides convincing evidence

that the building has been located.
9

Figure 8. Wide angle reflection and refraction profile performed at about 400 MHz

near the OCAF. Arrow 1 points to the

directly coupled air wave, followed by the

directly coupled ground wave (arrow 2). All

other events become parallel with the ground

wave. The slope of the ground wave corresponds to n = 1.28, equivalent to an approximate snow density of 0.33 g/cm3. Bright

spots and noise bands are artifacts of the

automatic gain control used to amplify the

weak air wave.

buried building after it was abandoned in the

mid-1970’s.*

The migration dielectric constant of 1.93 is an

integrated value. The fact that ε increases with

depth is demonstrated by the results of a WARR

profile taken near the site (Fig. 8). The WARR

used two Model 3102 units, one as a transmitter

and the other as receiver; only the transmitter

was moved. At the expense of noise amplification, automatic gain control was applied to this

record to make visible the first event, the weak

direct air wave coupling. The time–distance slope

of the direct air wave coupling gives a velocity of

31.0 cm/ns, an error of about 3% over the actual

value of 30 cm/ns. The ground wave slope gives

a value of n = 1.28. This value of n corresponds to

a near-surface density of about 0.35 g/cm3 and,

therefore, represents only the upper layers of

snow. All subsequent subsurface reflections become parallel with the ground wave as they refract into the faster near-surface media; thus, refractions spend more time near the surface.

New water well and nearby sewage sumps

The new water well is located just south of the

main station (Fig. 5). It was being formed during

our visit. First, a shaft was melted with hot water

down through permeable snow to a depth of

about 60 m where water began to pond. This water was brought up, heated and returned to enlarge the pool. As the pool grew, a cavity was created above it since the meltwater occupies less volume than the dense snow it replaces. At the time of

the survey, the surface of the pool was 70.1 m (230

ft) below the snow surface and its diameter was

thought to be approximately 9 m (30 ft). The air

bulb began at about 60 m depth and so there was

approximately 10 m of air space above the water

surface.

Three sewage sumps located nearby are labeled

utilidor vent, sump 1 and sump 2 on Figure 5. The

objective here was to determine if the radar could

detect these sumps and, if possible, measure their

lateral extent, known to be about 21 m. We also

hoped to obtain an effective dielectric constant of

deeper firn by using the diffractions from the well,

whose depth was known.

A 100-MHz time section profile along the line

PQ (Fig. 5) across the well is shown in Figure 9.

The 100-MHz transducer was used because the

sampling rate was sufficient to reproduce the signals at the necessary time range. The slight surface

elevation difference of about 2 m from the north to

the south end of the profile was inconsequential in

view of the large time range used to reach the well.

The wide hyperbola peak at 762-ns time delay is

the response to the water in the well, which is a

prominent target with large radar cross section

and a positive dielectric anomaly (higher dielectric constant than that of the snow). This is consistent with the phase polarity of the response; a response to the hemispherical air bulb, which has a

low radar cross section, would have the opposite

* Personal communication with A. Hogan, CRREL, 1995. phase because it is a negative dielectric anomaly.
A refractive index of 1.59 (ε = 2.53) gives an almost perfect hyperbolic fit to this diffraction, and

corresponds to an overburden average density of

about 0.7 g/cm3. Alternatively, given the time

delay and the measured depth to the water of 70.1

m, the effective refractive index for the firn

overburden is determined to be 1.63 (ε = 2.66).

Although the estimated bulb diameter is 9 m,

there is no evidence (e.g., two hyperbolae) of separate diffractions from each end of the bulb, as the

temporal displacement of their asymptotes

would be over 80 ns at the ends of the profile.

Therefore, the diffraction itself, centered exactly

at the center of the water well, is primarily a

response to the complete well surface, but

undoubtedly modified somewhat by the air bulb.

There are many other events in Figure 9, the

origins of which are not known. The area was extremely cluttered. Events with a slope corresponding to a refractive index near 1.3 are either

surface or near-surface objects. Event 2 in Figure

9 is a hyperbola that gives a refractive index of

1.46 (density = 0.55 g/cm3 at an approximate

depth of 29.5 m, assuming the object was directly

10

Figure 9. 100-MHz time section profile across the water well, the depth of which was 70.1 m. The asymptotic slopes

of the hyperbolic diffraction from the well (1) give an nm = 1.59; the slopes of the more shallow hyperbola (2) from an

unknown object give nm = 1.46; and the slopes of the resonant waves (3) generated by surface objects give nm = 1.36.

beneath the profile). The slopes of the linear sloping events throughout the record (e.g., event 3 in

Fig. 9) give a refractive index of 1.36 (density =

0.45 g/cm3). The accuracy of these measurements

is about 4%, based on the error of making a best

fit to the diffractions.

A migration of the water well profile is shown

in Figure 10. The time section profile had to be

compressed by a factor of two (subsequently

expanded) so that the migration aperture could

encompass most of the water well diffraction.

The migration collapses the hyperbolic diffraction from the well to a segment approximately 16

m wide. This is wider than the estimated bulb

diameter of 9 m and may be partly an artifact of

the algorithm and the finite pulse width, as theory (Yilmaz 1987) shows that a perfect diffraction

hyperbola generally collapses to this finite sized

form rather than to a singular point. For estimating the encroachment of the sumps, we have

assumed that the current diameter of the water

well could be as great as 16 m.

Three sumps in this area, sump 1 and sump 2,

and one below a utilidor vent south of the dome,
11

Figure 10. Migration of the water well profile seen in Figure 9. The central bright spot at 71-m

depth (arrow) is the water well and its width may be ascribable to a migration algorithm artifact

because the diffraction is almost a perfect hyperbola and should migrate to a point. More shallow

events in the profile are improperly migrated because of changing velocity with depth.

are marked in Figure 5. At the time of the survey,

sump 1 was believed to look as depicted in Figure

11, which is based on prior CRREL and Metcalf and

Eddy (M&E), Inc., measurements there and

CRREL studies of similar sumps in Greenland. The

surface of the central liquid pool was measured at

17.4 m below the snow surface during our surveys

and the zone of sewage-contaminated 0°C snow

was found the year before to extend radially about

21.3 m. At the extremities of the sump, the depth to

the sewage-soaked material increases about by 3

m. This sump is in use and thus there is a central

liquid pool and water in the upper portion of the

contaminated snow.

Figure 11. Two-dimensional depiction of

the disposition of sewage within sump 1 at

location A in Figure 5.
12

a. Line AC, which runs west from the sump 1 area. Arrows point to the response of

the sump at a depth of about 17 m.

Figure 12. 400-MHz time-section profiles (bottom) and their migrations.

The area marked sump 1 was profiled along

two lines (AB and AC) as shown in Figure 5. These

profiles along with their migrations are shown in

Figure 12. The migration used a value nm = 1.55,

obtained from the sump 1 diffractions, to calibrate

depth. The time section in Figure 12a (bottom)

along line AC shows the diffraction response of

the sump (arrow) to originate at an approximate

depth of 17 m. The migration of this profile (Fig.

12a, top) shows the sump response to extend only

about 7 m in the westerly direction, considerably

less than the 21 m expected on the basis of penetration rate measurements of holes melted with an

electric heater some time ago.

The time section profile in Figure 12b (bottom)

along line AB starts at the center of sump 1 and

passes near the utilidor vent at about 29 m and

over the sewage sump centered about there. As

shown in Figure 12a, the sump 1 response (arrow

A) occurs at a depth of about 17 m and seems to

extend only about 7 or 8 m northward. The diffraction response, which we believe is the utilidor roof
13

(arrow B), occurs at a delay of 70 ns and, given a

depth of 6.9 m from our verification survey, corresponds to an nm = 1.52. Although this value

agrees well with our migration refractive index of

1.54, snow nearer the surface is of less density, as

we have seen above, and is more likely to have an

n = 1.3. This would place the actual distance to

the roof at about 7.7 m at the 29-m distance,

b. Line AB, which runs from the sump 1 to the utilidor vent in Figure 5. Arrow A points to the sump

1 response and arrow B to the probable response of the utilidor vent. The vent response migrates to a slope,

which indicates increasing distance from the utilidor. The slope originates at 25 m and may indicate a

positional error. The sump response at the vent is probably the diffractions indicated as C. The spread of

sewage in both sumps suggested by the migration is believed to be far too small.

Figure 12 (cont’d).

which suggests that we may have been off the center of the utilidor. In addition, the time section migrates to a one-sided dipping reflection, rather

than a point, as would happen for a fixed target

(the roof) whose distance increases from the radar

receiver. The difficulty with this explanation is that

the dipping reflection appears to originate at a 25-

m distance. Resolution of this problem is not possi-
14

Figure 13. Two versions of the 400-MHz profile recorded at 300 ns across line FG over sump 2. The sump is

centered at the 50-m distance. The bottom profile represents an estimate of the actual reflective strength throughout

the sump and shows greater diffraction intensity below 12 m where frozen sewage begins. The later diffractions are

strong enough to make their asymptotes visible. The top profile equalizes the intensity of all events and reveals the

density horizons that subside toward the sump.

ble without better knowledge of our exact antenna

location, near-surface snow density structure and

any debris or other structures that may exist above

the roof.

The depth to contamination at the sump below

the utilidor vent had to be 9 m or less, since some

time ago that sump had filled to the level of the

floor of the utilidor. The depth could even be less,

since sewage was discharged up the utilidor about

13.4 m toward point O and could have raised the

level of the contamination in this area. We believe

that the response to this sewage is event C in Figure 12b. The radar data migration suggests that the

radius of the sump below the end of the utilidor is

about 5 m, but we expect that it is much larger.

Sump 2 was traversed from west to east along

line FG (Fig. 5). The center of the sump 2 area is

approximately 70 m from the center of the water
well. Prior CRREL and M&E measurements have

shown the depth to contamination at the center of

sump 2 to be approximately 12 m. Sump 2 is probably similar to the depiction in Figure 11, with a

radial extent of about 21 m and a maximum depth

of about 35 m. However, since this sump has not

received warm sewage for some time, no liquid

exists within it.

The 400-MHz time section profile over sump 2

between points F and G is shown in two versions

in Figure 13. All of the hyperbolic diffractions in

the profile can be matched well using a refractive

index of about 1.54. We used this value to calibrate

the depth scale, and it corresponds to an average

snow density of about 0.65 g/cm3. The signal intensities within the bottom profile are approximately proportional to the actual reflectivity

throughout the sump because signal loss with

range is compensated for by the radar system

Time-Range-Gain (TRG) function. Several closely

spaced diffractions, originating over the center of

the sump area, begin at an apparent depth of 4 m

and continue throughout the depth of the record.

Within these diffractions lies the stronger responses to the frozen sewage at just over 12 m depth.

The many diffractions that originate below 12 m

are probably from deeper portions of the sump,

which is expected to extend to a depth of about 35

m. These diffractions are so strong that their

asymptotes are highly visible, a consequence of

the off-axis strengthening of antenna directivity

shown in Figure 2.

The top profile of Figure 13 equalizes the gain

throughout the record so that all events are equally apparent, especially those from the density contrast interfaces, which appear to subside toward

the sump. This subsidence is consistent with

known increases in snow consolidation from

warming in the vicinity of such sumps. Snow consolidation is also apparent from the refractive indices measured at sumps 1 and 2; the values of 1.5 to

1.6 over the 16-m depth are higher than maximum

values (1.4) found over similar depths along the

tunnel survey.

A migration of the central section of this profile

is shown in Figure 14. Some of the peak signal

strengths along the profile scans are amplified to

bit saturation to allow us to view the deeper returns. The migration shows a coherent horizon at

about 14 m depth and then reflections that spread

asymmetrically to an approximate width (diameter) of 25 m at a depth of about 16 m. The sump 2

region seems to extend about 15 m to the west, but

this sump is known to be refrozen and to extend

radially about 20 m towards the water well. Therefore, we conclude that the contaminated firn

beyond a 15 m radius did not produce detectable

reflections.

15

Figure 14. Migration of the central section of the sump 2 profile using a migration velocity based on nm = 1.54 (density 0.65). The section indicates that the sewage spreads to an

estimated width (diameter) of 25 m, 15 m of which is towards the water well. Arrow points to

a coherent reflection at about 14 m depth.
16

Figure 15. Three parallel 400-MHz profiles recorded at 200 ns at the

far sump location (lines HI, JK, LM in Figure 5). Only line JK picked

up diffractions at depth.

In summary, the contaminated areas of sumps 1, 2 and the sump below

the utilidor vent seem well isolated

from the water well. The radar indicates about an 8-m radius for the water well and a spread of about 15 m for

the sump 2 contamination toward the

well. This leaves more than 45 m separation between the well and the nearest contamination. Since the well bulb

is below the contamination, the radar

suggests that there is about 55 m separation between the nearest contamination and the water well itself. However, since probes indicate that the radii

of the sewage sumps are about 21 m,

not 15 m, it is likely that the actual separation is closer to 50 m.

Far sump

This survey was done to verify the

location of an old sewage sump and to

estimate its lateral extent. The expected location from station drawings is at

point N and is labeled far sump in Figure 5, where three parallel survey lines

are located. The lines were 100 m long

and spaced 15 m apart. In January

1991, using hot point drills provided

by CRREL, M&E personnel determined that the depth to contamination

was approximately 12 m. The lateral

radius of this contaminated zone was

estimated to be about 21 m. This sump

has not been in use for many years and

has refrozen.

We used the 400-MHz transducer

unit at a time range of 200 ns to show

approximately 20 m of signal penetration into the firn. The three 100-m long

parallel time section profiles (lines HI,

JK and LM) are shown in Figure 15.

The profiles are 15 m apart. Only the

center line, JK, shows diffractions in

the area of the sewage sump at 50 to 55

m distance. An early hyperbola at 2.4

m depth is from air waves reflecting

off a surface object because its slope

gives a refractive index less than 1.1. A

series of hyperbolas originate at a

depth of about 6.5 m and extend vertically down

through the record. Their slopes give a refractive

index of 1.39 (ε = 1.93). The dip in the layering

horizons on either side of the sump are similar to

those seen around sump 2 in Figure 13 and is further evidence for firn subsidence around the

sumps. None of the diffractions originating near

12 m depth are of unusual intensity, but at the 16-

to 17-m depth, the diffractions become more in-
Figure 16. Migration of the profile along the centerline JK at the far sump. A concentration of sewage beginning at

about 14 m depth is apparent, but there is no indication of the lateral spreading reported to exist.

17

tense. The migration of this record (Fig. 16) picks

up these deeper targets, which probably represent layers of contaminated snow deeper in the

sump. The radar records again suggest less lateral

spread of contamination from the discharge point

than the 21 m estimated by M&E.

An additional profile, 133 m long, was run

from the center of the far sump back to the lift station (line NO in Fig. 5) to determine if any cavities

had been created by leaks along the sewer line

that serviced the far sump. Some years ago, a leak

along the line servicing sump 2 (see Fig. 5) created

a 1-m-diameter vertical shaft that was about 30 m

deep. A worker clearing snow from the line

almost fell into that shaft, which shortly after

became sump 1. Figure 17 shows the time section

of line NO. The time range is 400 ns and the depth

scale is based on nm = 1.60, derived from the deep

diffractions from the sump at point N. This value

gives a minimum depth scale because the shallow

diffractions from buried objects between 25 and

55 m away from the sump (these are too shallow

to be leaks) give nm = 1.30. The profile has been

horizontally filtered to remove most of the response to the firn layering and is presented in a

signal intensity format so that diffractions can be

viewed more easily. As in profile JK of Figure 15,

there are strong diffractions beginning at the center of the sewage sump (point N) at about 15 to 30

m depth. Strong diffractions, apparently from the

utilidor, also occur at point O. Migration of this

profile shows no sewage spread beyond about 10-

m radius at point N, considerably less than the 21

m estimated by M&E.

Several diffractions occur between the sump

and utilidor that could be leaks along the sewer

line. Although not easily visible in Figure 17, a

cluster of weak diffractions between 64 and 80 m

are candidates for shafts caused by leaks. The diffraction at 30 m depth about 93 m from N may be

frozen sewage at the base of such a shaft.

Proposed tunnel routes

ASTRO to main station

The two tunnel routes studied are shown in

Figure 18. The upper route is divided into sections lettered A, B and C. So much buried debris

was detected within the section A survey (originally 30 m wide) just west of the skiway that the

width of that section was increased by 10 m to the

south and 20 m to the north. Section D in Figure

18 is a narrow swath surveyed between the

ASTRO facility and the elevated dormitory. All

surveys consisted of parallel profiles, about 2.8 m

apart, running the length of the sections. The profiles are alphabetically lettered and may be located later in Figures 21 and 22.
18

Figure 17. 400-MHz time-section profile from the center of the far sump (point N) back toward the lift station. The diffractions

beginning at about 15 m depth at point N are responses to the frozen sewage, but there is no indication of the lateral spreading

previously reported because all these diffractions originate near point N. The bracket spans a cluster of weak diffractions whose depth

indicates that they may be an old sewer leak, and the arrow points to a deep anomaly of unknown origin.

0 100 200 300 400 m

Section A

Section D

Section B

Spase

Array

CAF

Geographic

South Pole

Elevated

Dorm

Taxiway

Skiway

Fuel

Arch

Grid North

(Greenwich Meridian)

Dome

Skylab

Section C

Bladder

 The profiles of lines D

and G within section A are

shown in Figure 19. The

accuracy of the distance scale

depended on accurate electronic marker recording at

the moment of passing the

flagged stations. This became

progressively more difficult

as the lines moved farther

from the flags and so distance accuracy is probably ±2

m at best. The depth scale is

calculated from the value of

nm = 1.4, which is the maximum found from diffractions

within the firn. Therefore,

this value gives the minimum possible depth to the

objects (apexes of the diffractions). The profiles are presented in a signal intensity

format that emphasizes only

the stronger events. Both profiles show a heavy

concentration of diffractions just west of the skiway. This concentration is characteristic of most

profiles in this section and is the most formidable

obstacle in the tunnel survey. Further to the west

Figure 18. Proposed tunnel routes. Sections A, B and

C run from the dome to the ASTRO and CARA (under

construction) astronomical facilities. Section D is a 10-

m wide section that extended 800 m from the ASTRO

building to the elevated dormitory across the skiway.

Fuel

Arch
19

Figure 19. Profiles of lines D and G along section A of the tunnel survey. The depth scale is based on ε= 1.93. Many hyperbolic

diffractions can be seen just west of the skiway. A horizon at 4- to 5-m depth is the work surface from previous operations at the

first pole station established in 1957.
20

Figure 20. Segments of lines CC–J that contain the many diffractions west of the skiway. The apexes of the diffractions rise as the transects progress to the north (toward line J).

All radar profiles from line CC (southernmost

line) to line J contained diffractions, with most

concentrated in the 85-m-wide strip just west of

the skiway. No diffractions were seen along lines

K through Q in this 85-m-wide area. These 85-mlong profile segments along with the skiway

itself are shown in Figure 20. Lines CC through A

show responses from distinct targets. The rebeyond the ASTRO complex several solitary diffractions may be seen. The location and depth of

all these diffractions are plotted later in Figure 21.

Also visible in Figure 19 is a horizon at about 3 to

4 m depth. This is believed to be dense snow

caused by traffic between the old and new stations during the early 1970’s when the new station was being constructed.
21

Figure 20 (cont’d).

maining lines A through J each show a continuum

of diffractions that represent a considerable

amount of debris ranging in depth from 6–12 m.

As shown in Figure 21, this debris resides in a line.

Perhaps it is an old trash dump.

The skiway, all of section A east of the skiway,

all of section B and almost half of section C are

clear. There are many indications of debris along

the tunnel route west of the ASTRO facility, and

also along the easterly half of section C in the vicinity of the fuel bladder by the taxiway. Some of

the dots in Figure 21 form linear patterns that may

indicate utility lines or orderly storage of abandoned equipment.

Most of the debris near the fuel bladder is located at a depth of less than 4.3 m. Since the top of the

tunnel will be at least 4.6 m below the surface,

most of the debris in this area should not be

a problem, and a tunnel route can be selected

to miss the few deep objects in this area. Alternatively, most of these objects could be dug up since

they are not deep.

The debris field just west of the skiway must

be avoided. That is possible by routing the tunnel

just north of this area where lines K through Q

showed no debris.

Scattered debris west of the ASTRO building is

located at depths that will cause it to interfere

with tunneling. However, safe routes through

this area are possible. Our route surveys enabled

us to find debris and assess the suitability of tunneling routes, but that work was not conducted to

pinpoint the location of each potential problem.

An additional radar survey for that purpose will

be needed just prior to tunneling.

ASTRO to elevated dormitory

This survey route (section D in Fig. 18) was

added to determine the feasibility of tunneling

along this route, since new station facilities prob-
22

Figure 21. Plan view of the primary tunnel survey. Dots represent radar targets and circled dots are the more intense

echoes that are probably from metal targets. Faint reflections may also be metallic targets but with a very small radar cross

section. Bars (west of the runway) represent a dense continuum of targets. Numbers beside the dots and bars are depths to

the targets in meters. Average line spacing is 2.8 m (not drawn to scale for clarity).

ably will be constructed in this area. The straight

route is approximately 800 m long and crosses the

skiway and the taxiway. Four lines were run at an

average spacing of 2.8 m. The 0-m mark is within

a few meters of the ASTRO building.

The results of this survey are shown in Figure

22, where dots mark the approximate location of

a diffraction response. Almost the entire route is

clear. The accuracy of line and anomaly placement is probably no better than ±5 m because the

lines had no intermediate survey marks.

CONCLUSIONS

Radar responses were recorded from numerous subsurface features of interest at the South

Pole. Reflections from features of known depth

and lateral extent helped calibrate findings. The

new water well gave a strong response and its

calculated depth was very close to its measured

depth. The old clean air facility was located. To

mark the spot, a 4-m bamboo pole was placed at

point Y in Figure 5. Near its top, a plywood dia-
23

Line

Line

Line

Line

C

A

D

B

ASTRO

Distance from ASTRO Building (m)

0 100 200 300 400 500 600 700 800

Section D 4.0 4.4 6.0

3.6

4.4

4.0

4.0

4.0

3.6 5.4

Elevated Dormatory

3.0

Lines are About 3.1m Apart

Figure 22. Plan view of the survey run between the ASTRO building and the elevated dormitory. Survey lines begin at the edge of the ASTRO building and terminate at approximately 800

m, about 10 m short of the base of the dormitory. Average survey line spacing is in meters. Dots

indicate radar targets with depths in meters indicated.

mond with a Y carved into it is wired to the bamboo. The pole was placed with 2.89 m of its length

above the snow surface.

Active and refrozen sewage sumps south of

the dome were found, but the radar did not detect

their full lateral extent as found in the past by other methods. These sewage sumps are well isolated from the water well. Poor detection of their

extent is probably attributable to the low reflectivity of frozen sewage, loss of signal strength at

depth, and loss of imaging ability because of the

data compression needed to accommodate the

migration algorithm. Improved imaging of subsurface structures near the dome would require

software that accommodates at least twice as

many scans (127) for the migration aperture. Successful imaging of unfrozen sewage at depth in

firn at McMurdo station is discussed in Arcone et

al. (1994).

Debris just west of the skiway along the tunnel

route initially proposed between ASTRO and the

main station appears to be large and extensive.

The tunnel should be routed just north of this

area. A few objects exist in the snow along this

new route, but a tunnel route can be found

among them with the help of radar.

The GPR was sensitive to many subsurface

changes in material properties, including contrasts in firn density caused by traffic. Distorted

snow layers around sewage sumps were clearly

visible. We did not experience any radio interference, but the radar clutter of surface and nearsurface targets would have precluded interpretation of some records had we not had advance

knowledge of the approximate location and

depth of features of interest. Future investigations to a depth of about 30 m should use a 400- to

600-MHz transducer. Higher frequencies for

greater resolution are available, but their depth of

penetration may be limited to less than about 20 m

by their lower power. Operation of the tape recorder and control unit outside the tracked vehicle

was limited by the cold weather, which shortened

the usable battery life from 3.5 to about 2 hours.

LITERATURE CITED

Annan, A.P., W.M. Waller, D.W. Strangway, J.R.

Rossiter, J.D. Redman and R.D. Watts (1975) The

electromagnetic response of a low-loss, 2-layer, dielectric earth for horizontal electric dipole excitation. Geophysics, 40(2): 285–298.

Annan, A.P. and J.L. Davis (1976) Impulse radar

profiling in permafrost. Radio Science, 11(4): 383–

394.

Arcone, S.A. (1991) Dielectric constant and layerthickness interpretation of helicopter-borne shortpulse radar waveforms reflected from wet and

dry river-ice sheets. IEEE Transactions on Geoscience

and Remote Sensing, 29(5): 768–777.

Arcone, S.A. (1995) Numerical studies of the radiation patterns of resistively loaded dipoles. Journal

of Applied Geophysics, 33: 39–52.

Arcone, S.A. and A.J. Delaney (1987) Helicopterborne short-pulse radar profiles of river-ice sheets

in Alaska. Journal of Glaciology, 97(1): 333–341.

Arcone, S.A., E.F. Chacho, Jr. and A.J. Delaney

(1992) GPR detection of unfrozen water in the Sagavanirktok flood plain, Alaska. Water Resources

Research, 28(11): 2925–2936.

Arcone, S.A., A.J. Delaney and W. Tobiasson (1994)

Subsurface radar investigations at the Pegasus ice

runway and Williams Field, McMurdo Station,

Antarctica. USA Cold Regions Research and Engineering Laboratory, CRREL Report 94-12.

Arcone, S.A., D.E. Lawson and A.J. Delaney (1995)

Short pulse radar wavelet recovery and resolution

of dielectric contrasts within englacial and basal
ice of Matanuska Glacier, Alaska. Journal of Glaciology, 41(137): 68–86.

Bogorodsky, V.V., C.R. Bentley and P.E. Gudmandsen (1985) Radioglaciology. Boston, Massachusetts:

D. Reidel Publishing Company.

Cumming, W.A. (1952) The dielectric properties of

ice and snow at 3.2 centimeters. Journal of Applied

Physics, 23(7): 768–773.

Delaney, A.J., S.A. Arcone and E.F. Chacho, Jr.

(1991) Winter short-pulse radar studies on the

Tanana River, Alaska. Arctic, 43: 244–250.

Engheta, N., C.H. Pappas and C. Elachi (1982) Radiation patterns of interfacial dipole antennas. Radio

Science, 17(6): 1557–1566.

Galinovsky, L. and K. Levin (1990) RADAN 3.0

(signal processing software). North Salem, New

Hampshire: Geophysical Survey Systems, Inc.

Hanninen, P. and S. Autio (Ed.) (1992) Proceedings,

IV International Conference on Ground Penetrating

Radar, 8–13 June 1992, Rovaniemi, Finland. Espoo,

Finland: Geological Survey of Finland, Special

Paper 16.

24

Kovacs, A. and A.J. Gow (1975) Brine infiltration

in the McMurdo Ice Shelf, McMurdo Sound, Antarctica. Journal of Geophysical Research, 80(15):

1957–1961.

Kovacs, A. and R.M. Morey (1979) Remote detection of massive ice in permafrost along the

Alyeska Pipeline and the pump station feeder gas

pipeline. In Proceedings of the Specialty Conference

on Pipelines in Adverse Environments, ASCE, New

Orleans, Louisiana, p. 268–279.

Kovacs, A., A.J. Gow, J.H. Cragin and R.M. Morey

(1982) The brine zone in the McMurdo Ice Shelf,

Antarctica. USA Cold Regions Research and Engineering Laboratory, CRREL Report 82-39.

Pilon, J. (Ed.) (1992) Proceedings, II International

Conference on Ground Penetrating Radar, Ottawa,

Canada, 26–28 May 1988. Ottawa: Canadian Research Council, Department of Energy, Mines and

Resources. Geological Survey of Canada Paper

90-4.

Yilmaz, O. (1987) Seismic Data Processing. Tulsa,

Oklahoma: Society of Exploration Geophysicists.
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

6. AUTHORS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS 15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

 OF REPORT OF THIS PAGE OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and

maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,

including suggestion for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington,

VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

For conversion of SI units to non-SI units of measurement consult Standard Practice for Use of the International System of Units (SI),

ASTM Standard E380-93, published by the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa. 19103.

Ground-penetrating radar studies were performed at South Pole Station, Antarctica, during January 1993 to

determine if subsurface obstructions exist along a planned tunnel route from the main station to the new astrophysical research area on the far side of the skiway, and if various man-made subsurface features such as

sewage sumps, a water well, utilidors and buried buildings could be located and delineated. The maximum

depth of interest for the tunnel survey was approximately 10 m. For it, a short-pulse antenna transducer with

its antenna bandwidth centered near 400 MHz was towed along the ground surface over multiple traverses to

cover an area up to 60 m wide. The survey extended from the South Pole Station fuel arch, across the skiway

and then to the CARA site (Center for Astrophysical Resarch in Antarctica). The radar profiles show reflections from density layering within the snow caused by traffic and diffractions from artificial features within 13

m depth. Debris is present in the snow west of the skiway and near the fuel bladder near the taxiway. Targets

within 100 m of the west side of the skiway are extensive, and appear to be metallic. The tunnel should be

routed in the clear area north of them. Targets near the fuel bladder are only 3 to 4 m below the surface. The

tunnel could go under them, but as a precaution they could be removed. An additional survey was run over

a 30-m-wide swath from the ASTRO facility at the CARA site to the new elevated dormitory, a distance of

approximately 800 m. This swath appears to be clear of any subsurface debris, except very near the dormitory.

December 1995

Ground-Penetrating Radar Investigation of the

Proposed Dome–CARA Tunnel Route, and

Utilities at South Pole Station, Antarctica DPP-872 0063

Steven A. Arcone, Wayne Tobiasson and Allan J. Delaney

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road CRREL Report 95-24

Hanover, New Hampshire 03755-1290

National Science Foundation

Arlington, Virginia 22230

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161.

Antarctica Ground-penetrating radar

Cold regions South Pole Station

GPR Tunnel survey

32

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL
13. ABSTRACT (CONT'D)

Surveys performed at several utility sites near the main station provided a general assessment of the dielectric properties of the firn, and tested the radar’s ability to delineate subsurface features and potential hazards.

Migrated, spatial images of the old clean air facility, the water well under development, and the several sewage sumps are presented. In general, the numerous vents, cables, antennas, etc., of the area clutter the profiles

with diffractions that complicate interpretation of the data without prior knowledge of some features. The

migrated images allowed approximations to be made as to the depths of sewage sumps, the water well and

the old buried clean air facility.