![](media/image1.jpeg){width="12.95in" height="13.250694444444445in"}

**In Cooperation with the Edwards Aquifer Authority**

**Helicopter Electromagnetic and Magnetic Survey Data and Maps, Seco
Creek Area, Medina and Uvalde Counties, Texas**

**By**

**Bruce D. Smith, David V. Smith, Patricia L. Hill, and Victor F.
Labson**

Number range CHAPTERThis report is preliminary and has not been reviewed
for conformity with U.S. Geological Survey editorial standards or with
North American Stratigraphic Code.

Any use of trade, product, or firm names is for descriptive purposes
only and does not constitute endorsement by the U.S. Government.

**Open-File Report 03-226**

![](media/image4.jpeg){width="1.2in" height="1.051388888888889in"}**U.S.
DEPARTMENT OF THE INTERIOR**

**U.S. GEOLOGICAL SURVEY**

**Table of Contents**

Abstract\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....ii

Introduction\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....1

Geologic
Setting\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....3

Hydrologic
Setting\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....6

Helicopter Geophysical
Survey\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....6

Apparent Resistivity
Maps\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...7

Digital
Data\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...9

Conclusions\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....10

Appendix.......................................................................................\...12

Abstract

A helicopter electromagnetic and magnetic (HEM) survey was completed of
a 209 square kilometer (81 square miles) area of the central Edwards
aquifer. This open-file report is a release of the airborne geophysical
data and a summary of the hydrologic application. The survey area was
centered on the Valdina Farms sinkhole along the Seco Creek drainage in
western Medina County, Texas. Flight lines were flown north south with
three east west tie lines to aid in leveling the magnetic data.
Additional lines were flown on each side of the Seco and Little Seco
Creek drainages. A five kilometer (4 mile) extension of 15 lines was
flown north of the main survey block centered on Seco Creek. This
digital data release contains the flight line data, grids, and maps of
the HEM survey data.

The Edwards aquifer in this area consists of three hydrologic zones:
catchment, recharge, and confined. The Glen Rose Formation is exposed in
the catchment area. The recharge zone is situated in the Balcones fault
zone where the Devils River Group of the Edwards aquifer has been
exposed by normal faults. The magnetic data is not discussed in depth
here, but does have high amplitude closed anomalies caused by shallow
igneous intrusives. The Woodard Cave Fault that separates the recharge
and catchment zones is in places associated with a weak linear magnetic
low.

The HEM data has been processed to produce apparent resistivities for
each of the six EM coil pairs and frequencies. Maps of the apparent
resistivity for the five horizontal coil pairs show that the catchment,
recharge, and confined zones all have numerous linear features that are
likely caused by structures, many of which have not been mapped. The
distribution of high resistivity areas reflects the lithologic
differences within the Trinity and Edwards aquifers.

**Introduction**

A successful high resolution airborne magnetic survey of the central
Edwards and Trinity aquifers (Smith and Pratt, 2003; Smith and others,
2002) set the stage for additional applications of airborne geophysical
surveys to hydrologic studies in the area. The U.S. Geological Survey
(USGS), as part of a geological, geophysical, and hydrologic study of
the Edwards aquifer, funded a helicopter electromagnetic and magnetic
(HEM) survey to demonstrate the application to map subsurface features
important in understanding and modeling the hydrology of the Edwards and
associated aquifers. The Edwards Aquifer Authority funded additional
flying to increase the survey area from 93 square kilometers (36 square
miles) to 209 square kilometers (81 square miles).
![](media/image5.wmf){width="6.959027777777778in"
height="3.7944444444444443in"}

**Figure 1** *Location of airborne geophysical surveys over the central
Edwards Aquifer system.*

The Seco Creek watershed was chosen for this detailed study (Figure 1)
for a number of reasons:

> 1\) the study area encompassed a typical stratigraphic section
> including the catchment, recharge, and confined areas,
>
> 2\) the survey area covered a north-south section of the Balcones
> Fault Zone containing a variety of structural styles,
>
> 3\) one of the most prominent recharge and diversion features, the
> Valdina Farms Sinkhole, is located in the central part of the survey
> area, and
>
> 4\) several USGS and Texas Bureau of Economic Geology (BEG) studies
> covered the area and are currently active.

The HEM survey used the RESOLVE^©^ system flown by Fugro Airborne
Surveys, which uses five horizontal coplanar coils and one vertical
coaxial coil. The specific frequencies are given in Table 1. The system
also includes in the bird (sensor housing) a total field magnetometer,
differential kinematic GPS, and laser altimeter. The helicopter carries
another differential GPS system, barometric and radar altimeters, and a
video camera. Electromagnetic noise from power lines and natural sources
(lightning) are also measured. The survey was flown with north-south
flight lines and a nominal line spacing of 200 m with a sensor elevation
of 30 m except as required for safety considerations and FAA
regulations. The system was calibrated before and after the survey on
the ground in the central part of the survey area away from power lines
and other cultural noise. System calibration was also checked at the
Fugro Airborne offices in Toronto when the system returned. In addition
four lines were flown along the Seco and Little Seco Creeks. These
flight lines were flown to provide data directly along the drainages
with consistent flight elevation and time (flight number).

**Table 1** Frequencies and sensitivities for the HEM survey.

  ----------------------- ----------------------- -----------------------
  COIL CONFIGURATION      FREQUENCY (Hz)          SENSITIVITY (ppm)

  Coplanar                386                     0.13

  Coplanar                1514                    0.12

  Coaxial                 3315                    0.06

  Coplanar                6122                    0.24

  Coplanar                25960                   0.44

  Coplanar                106400                  0.44
  ----------------------- ----------------------- -----------------------

**Geologic Setting**

Sedimentary rocks of the Seco Creek watershed are given in the
stratigraphic section shown in Figure 2 and are described in detail by
Maclay (1995) and Small and Clark (2000). The oldest, lower Cretaceous,
rocks are the upper and lower members of the Glen Rose Limestone which
is part of the Trinity Group. An evaporate unit is found at the base of
the upper member. These units have a thickness greater than 150 m (500
ft). Mapping in the area by the Texas Bureau of Economic Geology (Murray
and Collins, 2003) has not subdivided the Glen Rose Limestone. The
Devils River is divided into upper and lower parts in this stratigraphic
section (Figure 2) and are equivalent to the Segovia Formation (lower
Devils River) and Fort Terrett Formation (upper Devils River) as
described by Rose (1972). Small and Clark (2000) do not divide the
Devils River in this area. The upper Devils River is more cavernous. The
Georgetown formation at the top of the late Cretaceous section is rather
impervious limestone and marl.

The upper Cretaceous consists of several formations (Figure 2) including
(from oldest to youngest) the Del Rio Clay, Buda Limestone, Eagle Ford
Group, Austin Group, Anachacho Limestone, and Escondido Formation. The
Del Rio Clay is approximately 15 m (50 ft) thick. The Austin Group is
massive chalk to marly flaggy limestone. The Eagle Ford is about 22 m
(70 ft) and contains black shales. All of these units have a higher
electrical conductivity than the more massive limestones of the Edwards
and Trinity Groups. This high conductivity of the Del Rio Clay is used
in electrical logs as a stratigraphic marker.

The Tertiary formations consist of the Midway and Wilcox Groups which
together range in thickness from 200 to 500 feet thick. These units
consist of shales, sandstones, siltstones, and some limestone. The
Uvalde and Leona gravels overlay these units and are less than 100 feet
thick.

The Balcones fault zone is the major structural feature of the study
area. Uplift of the Edwards Plateau in the Miocene and subsidence of the
Gulf of Mexico created a zone of normal faults. This zone is defined by
a number of northeast trending faults (Figure 3) and is the southern end
of the Edwards plateau. Some cross faults trend northwest to southeast.
Most of the faults are normal with the downthrown side to the southeast
toward the Gulf of Mexico. The Woodard Cave fault is the contact between
the Trinity and Edwards Groups (Figure 3) in the Seco Creek area. It has
a maximum displacement of about 600 feet. Many of the faults are more
like fracture or shatter zones rather than sharp breaks. Some faults
have gouge and small boulders.

![](media/image6.wmf){width="5.626388888888889in"
height="6.579861111111111in"}

**Figure 2** Stratigraphic section for the Seco Creek area (Murray and
Collins, 2003).

![](media/image7.jpeg){width="6.0in" height="6.825in"}

**Figure 3.** Geologic map (Murray and Collins, 2003) of the four 7.5
minute quadrangles in the upper Seco Creek Watershed. Lithologic units
are given in Figure 2. North-South lines are the flight path for the HEM
survey. Black lines are faults (dashed where inferred). Seco Creek
occupies the yellow Quaternary areas in the central part of the survey
area.

**Hydrologic Setting**

The Trinty Group in the northwest part of the survey area is termed the
catchment zone since drainages cross this zone with presumed little
recharge to the Edwards Aquifer. The Trinity Group is much less
permeable than the Edwards Group but is locally cavernous. For example
during normal flow, Seco Creek flow disappears in sink holes just north
of the fault contact with the Edwards. There have been no studies of
possible interconnection of recharge paths between the Trinity and
Edwards in this area. However the relatively lower permeability due to
shales and marls of the Trinity makes it a lower confining unit for the
Edwards.

The Edwards Group exposed by the normal Balcones fault zone in the
central part of the survey area (Figure 3) is termed the recharge zone.
This part of the aquifer has a very high porosity and permeability
typical of a karstic terrain developed since the Miocene uplift.
Lithology, stratigraphy, diagensis, and selective dissolution
(karstification) account for the effective porosity and permeability of
the aquifer. Cave development is controlled by both lithology and
structure.

In addition to the Trinity and Edwards aquifers, the Leona and Uvalde
gravels constitute the other aquifers in the area. These aquifers have
not been studied in the same detail as the Trinity and Edwards.

Faults in the area may act to increase the permeability by causing the
development of fractures. Development of fault gouge may increase the
clay content of the fault zones and effectively reduce the permeability.
Clay zones could actually be aquitards impeding local groundwater flow.

**Helicopter Geophysical Survey**

Both electromagnetic and magnetic field measurements were made over the
survey area. Smith and Pratt (2003) briefly discuss magnetic data for
the survey area in the context of the larger high resolution
aeromagnetic survey of the central Edwards Aquifer. The main conclusion
at this stage of processing of the magnetic data is that a linear slight
magnetic low can be correlated with parts of the main Woodard Cave
fault. Additional processing of the magnetic data and ground follow up
surveys are needed before any interpretation of this magnetic feature
can be made. There appears to be no magnetic anomalies associated with
the numerous other structures. A Cretaceous age intrusive is marked by a
magnetic high in the northwest part of the survey (Figure 8 in Smith and
Pratt, 2003). There are no indications of igneous dikes in this
relatively high resolution magnetic survey. Data processing at this
point has concentrated on the electromagnetic field measurements and is
described below.

***Apparent Resistivity Maps***

Apparent resistivity is the resistivity of a homogeneous isotropic
volume that would give the same electromagnetic signal as measured by
the HEM system. Fugro Airborne as part of the contracted data processing
has computed the apparent resistivity for each frequency. The
computation is based on the pseudo-layer model (Fraser, 1978). Yin and
Hodges (2003) discuss this method of apparent resistivity calculation
and utilize it in an analysis of electrical anisotropy for this survey.
Figure 4 shows apparent resistivity maps for the five horizontal
coplanar coil frequencies (Table 1). The color scale has the same
stretch between the highest and lowest measured apparent resistivity for
each map. The highest apparent resistivity decreases an order of
magnitude as frequency decreases 1.5 orders of magnitude (see figure
caption), from 1300 to 150 ohm meters. The color scales have been used
to emphasize comparative high and low resistivity areas within each map
(at each frequency) rather than between maps. Note also that a
resistivity color scale is used so that high resistivity (low
conductivities) areas are in the warmer colors (reds) and areas of low
resistivities (high conductivities) in the cooler colors (blues).

In general each map in Figure 4 shows progressively (from 4a to 4e)
deeper sections of the earth. Smith and others (2003) discuss specific
variations based on preliminary resistivity depth sections. Each part of
the Edwards aquifer system is characterized by contrasting apparent
resistivities. The lowest apparent resistivities are associated with the
confining units in the southwest quadrant of the survey. The thick Del
Rio Clay is source of the low resistivities. The electrically resistive
Buda Limestone, stratigraphically above the clay, is found in higher
elevations. Gravels along the drainages are also more resistive than
many of the older confining layers.

The central northwest trending highest resistivities are from the
exposed parts of the Devils River. The high resistivities at 100 and 25
kHz (Figure 4a and 4b) suggest a difference within the Devils River that
correlates with the upper and lower divisions shown in Figure 4. The
geophysical maps show more detail and precise locations than the
geologic map. Lower apparent resistivities in the area of the lower
Devils River at 400 Hz (northern part of the catchment zone) suggest
that the more conductive upper Glen Rose influences these apparent
resistivities.

![](media/image8.jpeg){width="5.794444444444444in"
height="8.020833333333334in"}Figure 4. Apparent resistivity maps for
each horizontal coplanar coil pair. High resistivities (warm colors) for
each frequency are (rounded up): a. 1300, b. 800, c. 500, d. 300, e. 150
ohm meters. The distance scale is 4 km or 2.5 miles (see also Plate 1).

Moderate resistivities in the northwest part of the survey area can be
attributed to the Glen Rose Formation. The upper Glen Rose just north of
the Woodard Cave fault maybe somewhat more conductive than the lower
unit further to the north. The upper and lower Glen Rose appear to be in
fault contact. There is an interesting but unexplained area of high
resistivity in the upper Glen Rose along the northern part of Seco Creek
(the northern extension of the central part of the survey area). The
higher resistivity could be due to a more resistive limestone lithology
at depth.

Linear apparent resistivity features correlate with known structures and
suggest structures that have not been mapped. The narrow low resistivity
trough in the southeast corner of the survey area (Figure 4) generally
corresponds to a mapped graben (Figure 3) in the same area but can be
much better defined from the geophysical maps since the graben structure
is not exposed. The northeast trending structure that causes this
graben, correlates with linear features in the confined zone to the west
suggesting it extends further to the west than mapped. Other narrow
zones in the confining units are suggestive of other similar structures
that are covered. High resistivity linear features in the Edwards
recharge area suggest structures along which there may be increased
permeability due to fracturing or karstification.

***Digital Data***

Flight line data is given in an ASCII database in the directory
[linedata](../../linedata). The position is given in lattitude and
longitude as well as UTM coordinates. The raw GPS positioning data for
the survey is in NAD83 (zone 14N) but has been reprocessed to NAD27
(zone 14N) in the database. The header for each channel is given in the
txt file in the directory. Each channel is described in the contractors
report given in the appendix and the [reports](../../reports) directory.

Grids of the magnetic field data and the apparent resistivities for the
horizontal coplanar coil pairs are given in the [grids](../../grids)
directory. The apparent resistivities have been corrected for system
drift and calibrations as described in the contractor's report (appendix
and [reports](../../reports) directory). The grid cell size is 50 m.
This is large in comparison to the measurement spacing along flight
lines (about 3 m) because the spacing between flight lines is larger
than the measurement interval. The grids are in grid exchange format
([Grids\\gxf_grid_documentation.pdf](../../grids/gxf_grid_documentation.pdf)),
a "standard" of the geophysical industry used in many map display
programs.

The directory [MapImages](../../MapImages) contains geotiff (UTM
projected tif files) of the grids. Each file has an associated world
file (tfw). In addition this directory contains AutoCad format files
(extension dxf) of the flight lines. These files are georeferenced to
the NAD27 projection. Plate 1 (pocket) shows plots of the map images.

**Conclusions**

The HEM survey of the Seco Creek area has mapped both the magnetic and
electrical characteristics of geologic and hydrologic features from the
near surface to depths on the order of 100 m. The magnetic survey data
has not been discussed in detail here but does show some anomalies
possibly associated with structures and a few high amplitude anomalies
related to igneous intrusives. The HEM data has been processed to
produce apparent resistivity maps. These maps show that the catchment,
recharge, and confined zones all have numerous linear features that
reflect exposed and covered structures. These structures are important
in understanding and modeling the hydrology of each zone. There are
areas of relatively high resistivity in the catchment and recharge zones
that reflect lithologic differences perhaps related to stratigraphic
changes.

**References**

Elliott, W.R. and Veni, G., 1994, The Caves and Karsts of Texas:
National Speleological Society Convention Guidebook, 342 p.

Haung, H. and Fraser, D.C., 1996, The differential parameter method for
multifrequency airborne resistivity mapping: Geophysics, vol. 61, p.
100-109.

Fraser, D.C., 1978, Resistivity Mapping with an Airborne Multicoil
Electromagnetic System: Geophysics, vol. 43, p. 144-172.

Maclay, R.W., 1995, Geology and Hydrology of the Edwards Aquifer in the
San Antonio Area, Texas: U.S. Geological Survey Water Resources
Investigations Report 95-4186, 64p.

Murray, K.E. and Collins, E.W., 2003, GIS Compilation of Geologic Map
Data for the Seco Creek Area, Medina County, Texas: U.S. Geological
Survey, Open File Report, in preparation.

Small, T.A. and Clark, A.K., 2000, Geologic Framework and Hydrogeologic
Characteristics of the Edwards Aquifer Outcrop, Medina County Texas:
U.S. Geological Survey Water Resources Investigations Report 00-4195.

Smith, B.D., Irvine, R., Blome, C., Clark, A.K., and Smith, D.V., 2003,
Number range CHAPTERPreliminary Results, Helicopter Electromagnetic and
Magnetic Survey of the Seco Creek Area, Medina and Uvalde Counties,
Texas: Proceedings from the Symposium on the Application of Geophysics
to Engineering and Environmental Problems, Environmental and Engineering
Society, 15p.

Smith, D.V. and Pratt, D., 2003, Advanced Processing and Interpretation
of the High Resolution Aeromagnetic Survey Data over the Central Edwards
Aquifer, Texas: Proceedings from the Symposium on the Application of
Geophysics to Engineering and Environmental Problems, Environmental and
Engineering Society, 11p.

Smith, D.V., Smith, B.D., and Hill, P.L., 2002, Aeromagnetic Survey of
Medina and Uvalde Counties, Texas: A Web Site for Distribution of Data,
OFR-02-0049.

U. S. Geological Survey, 1999, Geologic Framework and Hydrologic
Properties of the Seco Creek Watershed, Texas, Fact Sheet FS-104-98, 4
p.

Yin, C. and Hodges, G., Identification of Electrical Anisotropy from
Helicopter EM Data, Proceedings from the Symposium on the Application of
Geophysical methods Engineering and Environmental Problems,
Environmental and Engineering Society, 12p.

![](media/image9.png)

**Report \# 6025**

**Logistics Report**

**Helicopter-borne**

**RESOLVE Electromagnetic and Magnetic**

**Geophysical Survey**

**Seco Creek, Texas**

**Prepared by:**

**Fugro Airborne Surveys**

**2270 Argentia Road**

**Mississauga (Toronto), Ontario, Canada L5N 6A6**

**For:**

**the United States Geological Survey**

**October 2002**

**By: Michael J. Cain, P.Eng.**

**Fugro Airborne Surveys Toronto, Canada**

**SUMMARY**

This report describes the logistics and results of a RESOLVE EM and
magnetic airborne geophysical survey carried out for the United States
Geological Survey over the Seco Creek area, Texas. Total coverage of the
survey blocks amounted to 953 miles (1534 kilometres) over 2 survey
blocks and several lines following the creeks through the survey area.
The survey was flown from May 21 to 27, 2002.

The purpose of the survey was to map the conductive and magnetic
properties of Seco Creek and the surrounding area. This was accomplished
by using a RESOLVE multi-coil, multi-frequency electromagnetic system
supplemented by a high sensitivity cesium magnetometer. A GPS electronic
navigation system ensured accurate positioning of the geophysical data.

The RESOLVE system comprises of five coplanar coil pairs and one coaxial
coil pair with a frequency spread of 386 Hz to 106 400 Hz. This system
provided optimum definition of the conductive properties of the Earth's
layering in the top 100 m.

TABLE OF CONTENTS

**1.0 INTRODUCTION 1.[1](#introduction)**

2.0 SURVEY EQUIPMENT AND PROCEDURES
2.[1](#survey-equipment-and-procedures)

2.1 Electromagnetic System 2.[1](#electromagnetic-system)

2.2 Magnetometer 2.[4](#magnetometer)

2.3 Magnetic Base Station 2.[4](#magnetic-base-station)

2.4 Radar Altimeter 2.[5](#radar-altimeter)

2.5 Analog Recorder 2.[5](#analog-recorder)

2.6 Digital Data Acquisition System
2.[6](#digital-data-acquisition-system)

2.7 Video Flight Path Recording System
2.[7](#video-flight-path-recording-system)

2.8 Navigation (Global Positioning System)
2.[7](#navigation-global-positioning-system)

2.9 Field Workstation and Data Verification
2.[9](#field-workstation-and-data-verification)

3.0 PRODUCTS AND PROCESSING TECHNIQUES
3.[1](#products-and-processing-techniques)

3.1 Base Maps (optional) 3.[1](#base-maps)

3.2 Apparent Resistivity 3.[2](#apparent-resistivity)

3.3 EM Magnetite (optional) 3.[3](#em-magnetite-optional)

3.4 Total Magnetic Field 3.[4](#total-magnetic-field)

3.5 Calculated Vertical Magnetic Gradient (optional)
3.[4](#calculated-vertical-magnetic-gradient-optional)

3.6 Magnetic Derivatives (optional)
3.[4](#magnetic-derivatives-optional)

3.7 Multi-channel Stacked Profiles (optional)
3.[5](#multi-channel-stacked-profiles-optional)

3.8 Contour, Colour and Shadow Map Displays (optional)
3.[6](#contour-colour-and-shadow-map-displays)

3.9 Resistivity-depth Sections (optional)
3.[6](#resistivity-depth-sections-optional)

4.0 CONCLUSIONS AND RECOMMENDATIONS
4.[1](#conclusions-and-recommendations)

APPENDIX A LIST OF PERSONNEL

APPENDIX B ARCHIVE DESCRIPTION

APPENDIX C PROCESSING LOG

APPENDIX D BACKGROUND INFORMATION

D.1 Resistivity Mapping

D.2 Reduction of Geologic Noise

D.3 Magnetics

APPENDIX E FLIGHT LOGS

APPENDIX F TESTS AND CALIBRATIONS

**FIGURES**

**Figure 1.1 Seco Creek area, Texas.
1.[3](#figure-1.1-seco-creek-area-texas.)**

**TABLES**

**Table 1.1 Breakdown for the Seco Creek Survey
1.[1](#table-1.1-breakdown-for-the-seco-creek-survey)**

**Table 2.1 The Analog Profiles, RESOLVE System
2.[6](#table-2.1-the-analog-profiles-resolve-system)**

**Table 3.1 Survey Products 3.[2](#table-3.1-survey-products)**

# 1.0 INTRODUCTION

A RESOLVE electromagnetic and magnetic survey was flown for the United
States Geological Survey over the Seco Creek area, Texas. Details of the
survey areas are shown in Table 1.1

+-----------------+------------------+-----------+--------------------+
| **Block/Line**  | **Line Spacing** | **Line    | **Total distance** |
|                 |                  | Di        |                    |
|                 |                  | rection** |                    |
+-----------------+------------------+-----------+--------------------+
| Block 1         | 200 metres       | 0°        | 1370 km            |
|                 |                  |           |                    |
|                 | 655 feet         |           | 851 miles          |
+-----------------+------------------+-----------+--------------------+
| Block 2         | 200 metres       | 0°        | 54 km              |
|                 |                  |           |                    |
| (north          | 655 feet         |           | 33.6 miles         |
| extension)      |                  |           |                    |
+-----------------+------------------+-----------+--------------------+
| River lines     | 200- 250 metres  | variable  | 110 km             |
|                 |                  |           |                    |
|                 | 655-820 feet     |           | 68.4 miles         |
+-----------------+------------------+-----------+--------------------+
|                 |                  | **TOTAL** | **1534 km**        |
|                 |                  |           |                    |
|                 |                  |           | **953 miles**      |
+-----------------+------------------+-----------+--------------------+

######## 

######## **Table 1.1 Breakdown for the Seco Creek Survey**

Total coverage of the survey blocks amounted to 953 miles over 2 survey
blocks and 2 river sections. The survey was flown from May 21 to 27,
2002. The blocks were flown in an azimuthal direction of 0°. Three tie
lines were flown over block 1 perpendicular to the flight lines. Figure
1.1 displays the layout and location of the survey blocks.

Ancillary equipment consisted of a radar altimeter, a video camera,
analog and digital recorders, and an electronic navigation system. The
instrumentation was installed in an Ecureuil AS350-B2 turbine helicopter
(registration CF-ZTA) which was provided by Questral Helicopters Ltd.
The helicopter flew at an average airspeed of 70 mph (113 km/h) with an
average EM sensor height of approximately 110 feet (33.5 metres).

Section 2 provides details on the survey equipment, the data channels,
their respective sensitivities, and the navigation/flight path recovery
procedure.

######### 

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######### 

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######### 

######### ![](media/image10.jpeg){width="6.0in" height="5.263888888888889in"}

######### 

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######### 

######### 

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######### 

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######### **Figure 1.1 Seco Creek area, Texas.**

######### 

#   {#section-23 .unnumbered}

# 2.0 SURVEY EQUIPMENT AND PROCEDURES

This section provides a brief description of the geophysical
instruments, quality control and calibration procedures used to acquire
the survey data.

##### 

##### 2.1 Electromagnetic System

Model: RESOLVE

Type: Towed bird, symmetric dipole configuration operated at a nominal
survey altitude of 98 feet (30 metres). Coil separation is 7.9 metres
for 400 Hz, 1500 Hz, 6200 Hz, 25,000 Hz and 100,000 Hz and 9.0 metres
for the 3300 Hz coil-pair.

Coil orientations/frequencies: [orientation]{.underline}
[nominal]{.underline} [actual]{.underline}

coplanar 400 Hz 386 Hz

coplanar 1 500 Hz 1 514 Hz

coaxial 3 300 Hz 3 315 Hz

coplanar 6 200 Hz 6 122 Hz

coplanar 25 000 Hz 25 960 Hz

coplanar 100 000 Hz 106 400 Hz

Channels recorded: 6 in-phase channels

6 quadrature channels

2 monitor channels

Sensitivity: 0.13 ppm at 400 Hz CP

0.12 ppm at 1 500 Hz CP

0.06 ppm at 3 300 Hz CX

0.24 ppm at 6 200 Hz CP

0.44 ppm at 25 000 Hz CP

0.44 ppm at 100 000 Hz CP

Sample rate: 10 per second, equivalent to 1 sample every 3.5 m, at a
survey speed of 125 km/h.

The electromagnetic system utilizes a multi‑coil coaxial/coplanar
technique to energize conductors in different directions. The coaxial
coil is vertical with its axis in the flight direction. The coplanar
coils are horizontal. The secondary fields are sensed simultaneously by
means of receiver coils which are maximally coupled to their respective
transmitter coils. The system yields an in-phase and a quadrature
channel from each transmitter‑receiver coil‑pair.

Calibration of the system during the survey uses the Fugro AutoCal
automatic, internal calibration process. At the beginning and end of
each flight, and at intervals during the flight, the system is flown up
to high altitude to remove it from any "ground effect" (response from
the earth). Any remaining signal from the receiver coils (base level) is
measured as the zero level, and removed from the data collected until
the time of the next calibration. Following the zero level setting,
internal calibration coils, for which the response phase and amplitude
have been determined at the factory, are automatically triggered -- one
for each frequency. The on-time of the coils is sufficient to determine
an accurate response through any ambient noise. The receiver response to
each calibration coil "event" is compared to the expected response (from
the factory calibration) for both phase angle and amplitude, and the
applied phase and gain corrections adjusted to bring the data to the
correct value.

In addition, the output of the transmitter coils are continuously
monitored during the survey, and the applied gains adjusted to correct
for any change in transmitter output (due to heating, etc.)

Because the internal calibration coils are calibrated at the factory (on
a resistive halfspace) ground calibrations using external calibration
coils on-site are not necessary for system calibration. A check
calibration may be carried out on-site to ensure all systems are working
correctly. All system calibrations will be carried out in the air, at
sufficient altitude that there will be no measurable response from the
ground.

The internal calibration coils are rigidly positioned and mounted in the
system relative to the transmitter and receiver coils. In addition, when
the internal calibration coils are calibrated at the factory, a rigid
jig is employed to ensure accurate response from the external coils.

Using real time Fast Fourier Transforms and the calibration procedures
outlined above, the data will be processed in real time from measured
total field at a high sampling rate to in-phase and quadrature values at
10 samples per second.

##### 2.2 Magnetometer

Model: Fugro AM102 processor with Geometrics G822 sensor

Type: Optically pumped cesium vapour

Sensitivity: 0.01 nT

Sample rate: 10 per second

The magnetometer sensor is housed in the EM bird, 29 m below the
helicopter.

##### 2.3 Magnetic Base Station

Model: Fugro CF1

Type: Digital recording proton precession

Sensitivity: 0.10 nT

Sample rate: 1 second intervals

The base station was located in a magnetically quiet area away from
cultural interference. The clock on the base station was synchronized
with the airborne magnetometer to UTC time, permitting subsequent
removal of the diurnal variation. The magnetic base station was located
at approximately WGS84 latitude 29°21.87'N and longitude 99° 9.92'W.

##### 2.4 Radar Altimeter

Manufacturer: Honeywell/Sperry

Model: AA 330

Type: Short pulse modulation, 4.3 GHz

Sensitivity: 0.3 m

The radar altimeter measures the vertical distance between the
helicopter and the ground. This information is used in the processing
algorithm that determines conductor depth.

##### 2.5 Analog Recorder

Manufacturer: RMS Instruments

Type: DGR33 dot‑matrix graphics recorder

Resolution: 4x4 dots/mm

Speed: 1.5 mm/sec

The analog profiles are recorded on chart paper in the aircraft during
the survey. Table 2-1 lists the geophysical data channels and the
vertical scale of each profile.

+---------------+-----------------------------------+------------------+
| **Channel**   | **Parameter**                     | **Scale**        |
|               |                                   |                  |
| **Name**      |                                   | **units/mm**     |
+---------------+-----------------------------------+------------------+
| > 400I        | coaxial in-phase (400 Hz)         | 5 ppm            |
+---------------+-----------------------------------+------------------+
| > 400Q        | coaxial quad (400 Hz)             | 5 ppm            |
+---------------+-----------------------------------+------------------+
| > 1K5I        | coplanar in-phase (1500 Hz)       | 5 ppm            |
+---------------+-----------------------------------+------------------+
| > 1K5Q        | coplanar quad (1500 Hz)           | 5 ppm            |
+---------------+-----------------------------------+------------------+
| > 6K2I        | coplanar in-phase (6200 Hz)       | 10 ppm           |
+---------------+-----------------------------------+------------------+
| > 6K2Q        | coplanar quad (6200 Hz)           | 10 ppm           |
+---------------+-----------------------------------+------------------+
| > 1X8I        | coaxial in-phase (3300 Hz)        | 10 ppm           |
+---------------+-----------------------------------+------------------+
| > 1X8Q        | coaxial quad (3300 Hz)            | 10 ppm           |
+---------------+-----------------------------------+------------------+
| > 25KI        | coplanar in-phase (25000 Hz)      | 20 ppm           |
+---------------+-----------------------------------+------------------+
| > 25KQ        | coplanar quad (25000 Hz)          | 20 ppm           |
+---------------+-----------------------------------+------------------+
| > 100I        | coplanar in-phase (100000 Hz)     | 20 ppm           |
+---------------+-----------------------------------+------------------+
| > 100Q        | coplanar quad (100000 Hz)         | 20 ppm           |
+---------------+-----------------------------------+------------------+
| > ALTL        | altimeter (laser)                 | 3 m              |
+---------------+-----------------------------------+------------------+
| > ALTR        | altimeter (radar)                 | 3 m              |
+---------------+-----------------------------------+------------------+
| > MAGC        | magnetics, coarse                 | 20 nT            |
+---------------+-----------------------------------+------------------+
| > MAGF        | magnetics, fine                   | 2.0 nT           |
+---------------+-----------------------------------+------------------+
| > 2SP         | coplanar spherics monitor         |                  |
+---------------+-----------------------------------+------------------+
| > 2PL         | coplanar power line monitor       |                  |
+---------------+-----------------------------------+------------------+
| > 1KPA        | altimeter (barometric)            | 30 m             |
+---------------+-----------------------------------+------------------+
| > 2TDC        | internal (console) temperature    | 1º C             |
+---------------+-----------------------------------+------------------+
| > 3TDC        | external temperature              | 1º C             |
+---------------+-----------------------------------+------------------+

######## **Table 2.1 The Analog Profiles, RESOLVE System**

##### 2.6 Digital Data Acquisition System

Manufacturer: RMS Instruments

Model: DGR 33

Recorder: SanDisk 48-64 Mb flash cards

The data are stored on PCMCIA flash cards and are transferred to the
field workstation PC at the survey base for verification, backup and
preparation of in-field products.

##### 2.7 Video Flight Path Recording System

Type: VHS Colour Video Camera (NTSC)

Model: AG 2400/WVCD132

Fiducial numbers are recorded continuously and are displayed on the
margin of each image. This procedure ensures accurate correlation of
analog and digital data with respect to visible features on the ground.

##### 2.8 Navigation (Global Positioning System) 

[Airborne Receiver for Navigation]{.underline}

Model: Ashtech Glonass GG24

Type: SPS (L1 band), 24-channel, C/A code at 1575.42 MHz,

S code at 0.5625 MHz, Real-time differential.

Sensitivity: -132 dBm, 0.5 second update

Accuracy: Manufacturer's stated accuracy is better than 10 metres

real-time

[Airborne Receiver for Processing]{.underline}

Model: Ashtech Z-Surveyor

Type: Code and carrier tracking of L1 band, 12-channel,

dual-frequency C/A code at 1575.42 MHz, and L2 P-code

at 1227 MHz

Sensitivity: 0.5 second update

Accuracy: Manufacturer's stated accuracy for differential corrected

GPS is better than 1 metre

[Base Station]{.underline}

Model: Ashtech Z-Surveyor

Type: Code and carrier tracking of L1 band, 12-channel,

dual-frequency C/A code at 1575.42 MHz, and L2 P-code

at 1227 MHz

Sensitivity: 0.5 second update

Accuracy: Manufacturer's stated accuracy for differential corrected

GPS is better than 1 metre

The Ashtech GG24 is a line of sight, satellite navigation system which
utilizes time-coded signals from at least four of forty-eight available
satellites. Both Russian GLONASS and American NAVSTAR satellite
constellations are used to calculate the position and to provide real
time guidance to the helicopter. The Ashtech system can be combined with
a RACAL or similar GPS receiver which further improves the accuracy of
the flying and subsequent flight path recovery to better than 5 metres.
The differential corrections, which are obtained from a network of
virtual reference stations, are transmitted to the helicopter via a
spot-beam satellite. For flight path processing an Ashtech Z-surveyor
was used as the mobile receiver and base station receiver. The mobile
and base station raw XYZ data are recorded, thereby permitting
post-survey processing for theoretical accuracies of better than 5
metres. The final navigation channels were produced from the Ashtech
Z-Surveyor GPS unit which was located on the EM sensor.

The GPS base station was run for a period of at least 24 hours to
obtained a master position for post processing. For the Seco Creek
survey the GPS station was located at latitude 29º 21\' 53.5493"N,
longitude 99º 09\' 55.2231"W at an elevation of 277.5 metres a.m.s.l.
The GPS records data relative to the WGS84 ellipsoid, which is the basis
of the revised North American Datum (NAD83).

##### 2.9 Field Workstation and Data Verification

A laptop computer is used at the survey base to verify data quality and
completeness. Flight data are transferred to the PC hard drive to permit
the creation of a Geosoft database. This process allows the geophysicist
to display both the positional and geophysical data on a screen or
printer.

# 3.0 PRODUCTS AND PROCESSING TECHNIQUES

##### 3.1 Base Maps 

Base maps of the survey areas are produced from published topographic
maps. These provide a relatively accurate, distortion-free base which
facilitates correlation of the navigation data to the UTM grid. The
original topographic maps are scanned to a digital format and combined
with geophysical data for plotting the final maps. All maps are created
using the following parameters:

[Projection Description]{.underline}:

Datum: NAD27

Ellipsoid: Clarke 1866

Projection: UTM (Zone: 14)

Central Meridian: 99º West

False Northing: 0

False Easting: 500000

Scale Factor: 0.9996

WGS84 to Local Conversion: Molodensky

X,Y,Z Datum Shifts: 8 -159 -175

######## **Table 3.1 Survey Products**

> Digital Geosoft GDB archive format on CD-ROM (2 copies)
>
> Digital grid archives in Geosoft GRD format on CD-ROM (2 copies)
>
> Survey report (2 copies)
>
> Analog chart records
>
> Flight path videocassettes (VHS format)

Note: Other products can be produced from existing survey data, if
requested.

##### 3.2 Apparent Resistivity

The apparent resistivity in ohm-metres (ohm-m) can be generated from the
in-phase and quadrature EM components for any of the frequencies, using
a pseudo‑layer half-space model. Resistivity maps portray all the EM
information for that frequency over the entire survey area. This
contrasts with discrete electromagnetic anomaly maps which provide
information only over interpreted conductors. The large dynamic range
makes the resistivity parameter an excellent mapping tool.

The preliminary resistivity maps and images are carefully inspected to
locate any lines or line segments which might require levelling
adjustments. Subtle changes between in-flight calibrations of the system
can result in line to line differences, particularly in resistive (low
signal amplitude) areas. If required, manual levelling is carried out to
eliminate or minimize resistivity differences which can be caused by
changes in operating temperatures. These levelling adjustments are
usually very subtle, and do not result in the degradation of anomalies
from valid bedrock sources.

After the manual levelling process is complete, revised resistivity
grids are created. The resulting grids can be subjected to a
microlevelling filter in order to smooth the data for contouring. The
coplanar resistivity parameter has a broad \'footprint\' which requires
very little filtering.

The apparent resistivities have been calculated for all five coplanar
frequencies and the coaxial frequency using the pseudo-layer half-space
model. Digital data are contained on the CD-ROM archives. Values are in
ohm-m on all final products.

##### 3.3 EM Magnetite (optional)

The apparent percent magnetite by weight is computed wherever magnetite
produces a negative in-phase EM response. This calculation is more
meaningful in resistive areas, and is not recommended for these survey
areas due to the moderately conductive, non-magnetic background and
sources of cultural interference.

##### 

##### 3.4 Total Magnetic Field 

The aeromagnetic data are corrected for diurnal variation using the
magnetic base station data. Manual adjustments are applied to any lines
that require levelling, as indicated by shadowed images of the gridded
magnetic data or tie line/traverse line intercepts. The IGRF gradient is
removed from the corrected total field data.

##### 3.5 Calculated Vertical Magnetic Gradient (optional)

The diurnally corrected total magnetic field data are subjected to a
processing algorithm which enhances the response of magnetic bodies in
the upper 500 m and attenuates the response of deeper bodies. The
resulting vertical gradient map provides better definition and
resolution of near-surface magnetic units. It also identifies weak
magnetic features which may not be evident on the total field map.
However, regional magnetic variations and changes in lithology may be
better defined on the total magnetic field map.

##### 3.6 Magnetic Derivatives (optional)

The total magnetic field data can be subjected to a variety of filtering
techniques to yield maps of the following:

-   enhanced magnetics

-   second vertical derivative

-   reduction to the pole/equator

-   magnetic susceptibility with reduction to the pole

-   upward/downward continuations

-   analytic signal

All of these filtering techniques improve the recognition of
near‑surface magnetic bodies, with the exception of upward continuation.
Any of these parameters can be produced on request.

##### 3.7 Multi-channel Stacked Profiles (optional)

Distance‑based profiles of the digitally recorded geophysical data can
be generated and plotted by computer. These profiles also contain the
calculated parameters that are used in the interpretation process.

##### 3.8 Contour, Colour and Shadow Map Displays 

The geophysical data were interpolated onto a regular grid using a
modified Akima spline technique. The resulting grid is suitable for
generating contour maps of excellent quality. The grid cell size used
was 50 metres or 1/4 of the line interval.

Colour maps are produced by interpolating the grid down to the pixel
size. The parameter is then incremented with respect to specific
amplitude ranges to provide colour \"contour\" maps.

##### 3.9 Resistivity-depth Sections (optional)

The apparent resistivities for all frequencies can be displayed
simultaneously as coloured resistivity-depth sections. The sections can
be plotted using the topographic elevation profile as the surface. The
digital terrain values, in metres a.m.s.l., are calculated from the GPS
Z-value minus the aircraft radar altimeter.

Resistivity-depth sections can be generated in three formats:

(1) Sengpiel resistivity sections, where the apparent resistivity for
    each frequency is plotted at the depth of the centroid of the
    in-phase current flow[^1]; and,

\(2\) Differential resistivity sections, where the differential
resistivity is plotted at the differential depth[^2].

\(3\) Occam[^3] or Multi-layer[^4] inversion.

Both the Sengpiel and differential methods are derived from the
pseudo-layer half-space model. Both yield a coloured resistivity-depth
section which attempts to portray a smoothed approximation of the true
resistivity distribution with depth. Resistivity-depth sections are most
useful in conductive layered situations, but may be unreliable in areas
of moderate to high resistivity where signal amplitudes are weak. In
areas where in-phase responses have been suppressed by the effects of
magnetite, the computed resistivities shown on the sections may be
unreliable. The differential resistivity technique was developed by
Dighem. It is more sensitive than the Sengpiel section to changes in the
earth\'s resistivity and it reaches deeper.

Both the Occam and Multi-layer Inversions compute the layered earth
resistivity model which would best match the measured EM data. The Occam
inversion uses a series of thin, fixed layers (usually 20 x 5m and 10 x
10m layers) and computes resistivities to fit the EM data. The
multi-layer inversion computes the resistivity and thickness for each of
a defined number of layers (typically 3-5 layers) to best fit the data.

# 4.0 CONCLUSIONS AND RECOMMENDATIONS

This report provides a description of the equipment, procedures and
logistics of the survey. The digital data included with this report
display the magnetic and conductive properties of the survey area.

It is recommended that image processing of existing geophysical data be
considered, in order to extract the maximum amount of information from
the survey results. Current software and imaging techniques often
provide valuable information on structure and lithology, which may not
be clearly evident on the contour and colour maps. These techniques can
yield images which define subtle, but significant, structural details.

A complete assessment and evaluation of the survey data should be
carried out by one or more qualified professionals who have access to,
and can provide a meaningful compilation of, all available geophysical,
geological and geochemical data.

Respectfully submitted,

**FUGRO AIRBORNE SURVEYS**

Michael J. Cain, P.Eng.

Geophysicist

# APPENDIX A

# 

### LIST OF PERSONNEL

The following personnel were involved in the acquisition, processing,
interpretation and presentation of data, of the RESOLVE airborne
geophysical survey carried out for the United States Geological Survey
over the Seco Creek area, Texas.

> David Miles Manager, Helicopter Operations
>
> Emily Farquhar Manager, Data Processing
>
> Brett Robinson Field Geophysicist
>
> Will Marr Geophysical Operator
>
> Luke Kukovica Pilot
>
> Michael Cain Project Geophysicist
>
> Russell Imrie Geophysical Data Processor
>
> Lyn Vanderstarren Drafting Supervisor
>
> Albina Tonello Secretary/Expeditor

All personnel are employees of Fugro Airborne Surveys, except for the
pilot who is an employee of Questral Helicopters.

# APPENDIX B

### 

### ARCHIVE DESCRIPTION

This CD-ROM contains final data archives of an airborne survey conducted
by Fugro Airborne Surveys on behalf of United States Geological Survey
over the Seco Creek area, Texas. Total coverage of the survey blocks
amounted to 953 miles (1534 kilometres) over 2 survey blocks and several
lines following the creeks through the survey area. The survey was flown
from May 21 to 27, 2002.

**Fugro Airborne Surveys Job #6025**

The archives contain three directories.

1.  Line Data: Geosoft GDB database with archive description.

2.  Grids: Grids in Geosoft GRD format for the following parameters:

```{=html}
<!-- -->
```
1.  Magnetic total field (IGRF corrected)

2.  5 coplanar resistivities

3\. Report: A digital copy of the operations report

[Projection Description]{.underline}:

Datum: NAD27

Ellipsoid: Clarke 1866

Projection: UTM (Zone: 14)

Central Meridian: 99º West

False Northing: 0

False Easting: 500000

Scale Factor: 0.9996

WGS84 to Local Conversion: Molodensky

X,Y,Z Datum Shifts: 8 -159 -175

EM PARAMETERS

FREQUENCY

orientation nominal actual COIL SPACING

\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-- \-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\--

coplanar 400 Hz 386 Hz 7.9 m

coplanar 1 500 Hz 1 514 Hz 7.9 m

coaxial 3 300 Hz 3 315 Hz 9.0 m

coplanar 6 200 Hz 6 122 Hz 7.9 m

coplanar 25 000 Hz 25 960 Hz 7.9 m

coplanar 100 000 Hz 106 400 Hz 7.9 m

DATABASE : 6025_Seco.GDB

====================================================

NUMBER OF DATABASE CHANNELS : 146

====================================================

1 - LINE DBS-INC 0.10 LINE NUMBER

2 - FLIGHT DBS-INC 0.10 FLIGHT NUMBER

3 - DATE DBS-INC 0.10 FLIGHT DATE

4 - FID DBS-INC 0.10 FIDUCIAL COUNTER

5 - UTC DBS-INC 0.10 UTC TIME

6 - ALTBIRDM DBS-INC 0.10 BIRD RADAR ALTIMETER (METRES)

7 - ALTBIRDR DBS-INC 0.10 BIRD RADAR ALTIMETER RAW (METRES)

8 - ALTLASER DBS-INC 0.10 BIRD LASER ALTIMETER PROCESSED (METRES)

9 - ALTRFT DBS-INC 0.10 HELICOPTER RADAR ALTIMETER RAW (FEET)

10 - BALT DBS-INC 0.10 BAROMETRIC ALTIMETER RAW (METRES)

11 - ALTBARO DBS-INC 0.10 BAROMETRIC ALTIMETER PROCESSED (METRES)

12 - CPI100K DBS-INC 0.10 COPLANAR INPHASE FULLY PROCESSED 100K HZ

13 - CPI1500 DBS-INC 0.10 COPLANAR INPHASE FULLY PROCESSED 1500 HZ

14 - CPI25K DBS-INC 0.10 COPLANAR INPHASE FULLY PROCESSED 25K HZ

15 - CPI400 DBS-INC 0.10 COPLANAR INPHASE FULLY PROCESSED 400 HZ

16 - CPI6200 DBS-INC 0.10 COPLANAR INPHASE FULLY PROCESSED 6200 HZ

17 - CPIR100K DBS-INC 0.10 COPLANAR INPHASE FILTERED 100K HZ

18 - CPIR1500 DBS-INC 0.10 COPLANAR INPHASE FILTERED 1500 HZ

19 - CPIR25K DBS-INC 0.10 COPLANAR INPHASE FILTERED 25K HZ

20 - CPIR400 DBS-INC 0.10 COPLANAR INPHASE FILTERED 400 HZ

21 - CPIR6200 DBS-INC 0.10 COPLANAR INPHASE FILTERED 6200 HZ

22 - CPPL DBS-INC 0.10 COPLANAR POWERLINE MONITOR

23 - CPPLR DBS-INC 0.10 COPLANAR POWERLINE MONITOR RAW

24 - CPQ100K DBS-INC 0.10 COPLANAR QUADRATURE FULLY PROCESSED 100K HZ

25 - CPQ1500 DBS-INC 0.10 COPLANAR QUADRATURE FULLY PROCESSED 1500 HZ

26 - CPQ25K DBS-INC 0.10 COPLANAR QUADRATURE FULLY PROCESSED 25K HZ

27 - CPQ400 DBS-INC 0.10 COPLANAR QUADRATURE FULLY PROCESSED 400 HZ

28 - CPQ6200 DBS-INC 0.10 COPLANAR QUADRATURE FULLY PROCESSED 6200 Hz

29 - CPQR100K DBS-INC 0.10 COPLANAR QUADRATURE FILTERED 100K HZ

30 - CPQR1500 DBS-INC 0.10 COPLANAR QUADRATURE FILTERED 1500 HZ

31 - CPQR25K DBS-INC 0.10 COPLANAR QUADRATURE FILTERED 25K HZ

32 - CPQR400 DBS-INC 0.10 COPLANAR QUADRATURE FILTERED 400 HZ

33 - CPQR6200 DBS-INC 0.10 COPLANAR QUADRATURE FILTERED 6200 HZ

34 - CPSP DBS-INC 0.10 COPLANAR SPHERICS MONITOR

35 - CPSPR DBS-INC 0.10 COPLANAR SPHERICS MONITOR RAW

36 - CXI3300 DBS-INC 0.10 COAXIAL INPHASE FULLY PROCESSED 3300 HZ

37 - CXIR3300 DBS-INC 0.10 COAXIAL INPHASE FILTERED 3300 HZ

38 - CXPL DBS-INC 0.10 COAXIAL POWERLINE MONITOR

39 - CXPLR DBS-INC 0.10 COAXIAL POWERLINE MONITOR RAW

40 - CXQ3300 DBS-INC 0.10 COAXIAL QUADRATURE FULLY PROCESSED 3300 HZ

41 - CXQR3300 DBS-INC 0.10 COAXIAL QUADRATURE FILTERED 3300 HZ

42 - CXSP DBS-INC 0.10 COAXIAL SPHERICS MONITOR

43 - CXSPR DBS-INC 0.10 COAXIAL SPHERICS MONITOR RAW

44 - DTMB DBS-INC 0.10 DIGITAL ELEVATION MODEL FROM BARO

45 - DTMBARO DBS-INC 0.10 PROCESSED DIGITAL ELEVATION MODEL FROM BARO

46 - DTMGPSZ DBS-INC 0.10 DIGITAL ELEVATION MODEL FROM GPSZ

47 - DTMZ DBS-INC 0.10 PROCESSED DIGITAL ELEVATION MODEL FROM GPSZ

48 - DEP100K DBS-INC 0.10 DEPTH 100K HZ FILTERED

49 - DEP1500 DBS-INC 0.10 DEPTH 1500HZ FILTERED

50 - DEP25K DBS-INC 0.10 DEPTH 25K HZ FILTERED

51 - DEP3300 DBS-INC 0.10 DEPTH 3300 HZ FILTERED

52 - DEP400 DBS-INC 0.10 DEPTH 400 HZ FILTERED

53 - DEP6200 DBS-INC 0.10 DEPTH 6200 HZ FILTERED

54 - DEP100K_NF DBS-INC 0.10 DEPTH 100K HZ NOT FILTERED

55 - DEP1500_NF DBS-INC 0.10 DEPTH 1500HZ NOT FILTERED

56 - DEP25K_NF DBS-INC 0.10 DEPTH 25K HZ NOT FILTERED

57 - DEP3300_NF DBS-INC 0.10 DEPTH 3300 HZ NOT FILTERED

58 - DEP400_NF DBS-INC 0.10 DEPTH 400 HZ NOT FILTERED

59 - DEP6200_NF DBS-INC 0.10 DEPTH 6200 HZ NOT FILTERED

60 - DDEP100K DBS-INC 0.10 DIFFERENTIAL DEPTH 100K HZ FILTERED

61 - DDEP1500 DBS-INC 0.10 DIFFERENTIAL DEPTH 1500HZ FILTERED

62 - DDEP25K DBS-INC 0.10 DIFFERENTIAL DEPTH 25K HZ FILTERED

63 - DDEP400 DBS-INC 0.10 DIFFERENTIAL DEPTH 400 HZ FILTERED

64 - DDEP6200 DBS-INC 0.10 DIFFERENTIAL DEPTH 6200 HZ FILTERED

65 - DDEP100K_NF DBS-INC 0.10 DIFFERENTIAL DEPTH 100K HZ NOT FILTERED

66 - DDEP1500_NF DBS-INC 0.10 DIFFERENTIAL DEPTH 1500HZ NOT FILTERED

67 - DDEP25K_NF DBS-INC 0.10 DIFFERENTIAL DEPTH 25K HZ NOT FILTERED

68 - DDEP400_NF DBS-INC 0.10 DIFFERENTIAL DEPTH 400 HZ NOT FILTERED

69 - DDEP6200_NF DBS-INC 0.10 DIFFERENTIAL DEPTH 6200 HZ NOT FILTERED

70 - CEN100K DBS-INC 0.10 CENTROID DEPTH 100K HZ FILTERED

71 - CEN1500 DBS-INC 0.10 CENTROID DEPTH 1500HZ FILTERED

72 - CEN25K DBS-INC 0.10 CENTROID DEPTH 25K HZ FILTERED

73 - CEN400 DBS-INC 0.10 CENTROID DEPTH 400 HZ FILTERED

74 - CEN6200 DBS-INC 0.10 CENTROID DEPTH 6200 HZ FILTERED

75 - CEN100K_NF DBS-INC 0.10 CENTROID DEPTH 100K HZ NOT FILTERED

76 - CEN1500_NF DBS-INC 0.10 CENTROID DEPTH 1500HZ NOT FILTERED

77 - CEN25K_NF DBS-INC 0.10 CENTROID DEPTH 25K HZ NOT FILTERED

78 - CEN400_NF DBS-INC 0.10 CENTROID DEPTH 400 HZ NOT FILTERED

79 - CEN6200_NF DBS-INC 0.10 CENTROID DEPTH 6200 HZ NOT FILTERED

80 - DIURNAL DBS-INC 0.10 DIURNAL CORRECTION APPLIED

81 - KPA1 DBS-INC 0.10 PRESSURE IN MBAR

82 - L100I DBS-INC 0.10 BASE LEVELED INPHASE 100K HZ

83 - L100Q DBS-INC 0.10 BASE LEVELED QUADRATURE 100K HZ

84 - L1K5I DBS-INC 0.10 BASE LEVELED INPHASE 1500 HZ

85 - L1K5Q DBS-INC 0.10 BASE LEVELED QUADRATURE 1500 HZ

86 - L1K7I DBS-INC 0.10 BASE LEVELED INPHASE 3300 HZ

87 - L1K7Q DBS-INC 0.10 BASE LEVELED QUADRATURE 3300 HZ

88 - L25KI DBS-INC 0.10 BASE LEVELED INPHASE 25K HZ

89 - L25KQ DBS-INC 0.10 BASE LEVELED QUADRATURE 25K HZ

90 - L400I DBS-INC 0.10 BASE LEVELED INPHASE 400 HZ

91 - L400Q DBS-INC 0.10 BASE LEVELED QUADRATURE 400 HZ

92 - L6K2I DBS-INC 0.10 BASE LEVELED INPHASE 6200 HZ

93 - L6K2Q DBS-INC 0.10 BASE LEVELED QUADRATURE 6200 HZ

94 - LAT_BIRD DBS-INC 0.10 LATITUDE BIRD GPS WGS84 (NAD83)

95 - LAT_HELI DBS-INC 0.10 LATITUDE HELI GPS WGS84 (NAD83)

96 - LAT4 DBS-INC 0.10 LATITUDE HELI GPS UNPROCESSED WGS84 (NAD83)

97 - LON_BIRD DBS-INC 0.10 LONGITUDE BIRD GPS WGS84 (NAD83)

98 - LON_HELI DBS-INC 0.10 LONGITUDE HELI GPS WGS84 (NAD83)

99 - LON4 DBS-INC 0.10 LONGITUDE HELI GPS UNPROCESSED WGS84 (NAD83)

100 - LSR1 DBS-INC 0.10 RAW LASER ALTIMETER, NO CONVERSION FACTOR

101 - MAG DBS-INC 0.10 FINAL TOTAL MAGNETIC FIELD IGRF REMOVED

102 - MAGD DBS-INC 0.10 DIURNAL CORRECTED TOTAL MAGNETIC FIELD

103 - IGRF DBS-INC 0.10 IGRF

104 - MAGSP DBS-INC 0.10 TOTAL MAGNETIC FIELD DESPIKED

105 - MAGUR DBS-INC 0.10 RAW TOTAL MAGNETIC FIELD

106 - RES100K DBS-INC 0.10 RESISTIVITY 100K HZ FILTERED

107 - RES1500 DBS-INC 0.10 RESISTIVITY 1500 HZ FILTERED

108 - RES25K DBS-INC 0.10 RESISTIVITY 25K HZ FILTERED

109 - RES3300 DBS-INC 0.10 RESISTIVITY 3300 HZ FILTERED

110 - RES400 DBS-INC 0.10 RESISTIVITY 400 HZ FILTERED

111 - RES6200 DBS-INC 0.10 RESISTIVITY 6200 HZ FILTERED

112 - RES100K_NF DBS-INC 0.10 RESISTIVITY 100K HZ NOT FILTERED

113 - RES1500_NF DBS-INC 0.10 RESISTIVITY 1500 HZ NOT FILTERED

114 - RES25K_NF DBS-INC 0.10 RESISTIVITY 25K HZ NOT FILTERED

115 - RES3300_NF DBS-INC 0.10 RESISTIVITY 3300 HZ NOT FILTERED

116 - RES400_NF DBS-INC 0.10 RESISTIVITY 400 HZ NOT FILTERED

117 - RES6200_NF DBS-INC 0.10 RESISTIVITY 6200 HZ NOT FILTERED

118 - DRES100K DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 100K HZ FILTERED

119 - DRES1500 DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 1500 HZ FILTERED

120 - DRES25K DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 25K HZ FILTERED

121 - DRES400 DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 400 HZ FILTERED

122 - DRES6200 DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 6200 HZ FILTERED

123 - DRES100K_NF DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 100K HZ NOT
FILTERED

124 - DRES1500_NF DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 1500 HZ NOT
FILTERED

125 - DRES25K_NF DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 25K HZ NOT
FILTERED

126 - DRES400_NF DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 400 HZ NOT
FILTERED

127 - DRES6200_NF DBS-INC 0.10 DIFFERENTIAL RESISTIVITY 6200 HZ NOT
FILTERED

128 - X DBS-INC 0.10 FINAL BIRD UTM X CLARK 1866 (NAD27)

129 - X_HELI DBS-INC 0.10 UTM X FROM HELI GPS CLARK 1866 (NAD27)

130 - Y DBS-INC 0.10 FINAL UTM Y CLARK 1866 (NAD27)

131 - Y_HELI DBS-INC 0.10 UTM X FROM HELI GPS CLARK 1866 (NAD27)

132 - Z_B DBS-INC 0.10 FINAL Z

133 - Z_H DBS-INC 0.10 Z FROM HELI GPS

134 - GPSZ4 DBS-INC 0.10 Z FROM HELI GPS RAW

135 - \_100I DBS-INC 0.10 RAW INPHASE 100K HZ

136 - \_100Q DBS-INC 0.10 RAW QUADRATURE 100K HZ

137 - \_1K5I DBS-INC 0.10 RAW INPHASE 1500 HZ

138 - \_1K5Q DBS-INC 0.10 RAW QUADRATURE 1500 HZ

139 - \_1K7I DBS-INC 0.10 RAW INPHASE 3300 HZ

140 - \_1K7Q DBS-INC 0.10 RAW QUADRATURE 3300 HZ

141 - \_25KI DBS-INC 0.10 RAW INPHASE 25K HZ

142 - \_25KQ DBS-INC 0.10 RAW QUADRATURE 25K HZ

143 - \_400I DBS-INC 0.10 RAW INPHASE 400 HZ

144 - \_400Q DBS-INC 0.10 RAW QUADRATURE 400 HZ

145 - \_6K2I DBS-INC 0.10 RAW INPHASE 6200 HZ

146 - \_6K2Q DBS-INC 0.10 RAW QUADRATURE 6200 HZ

========================================================================================

# APPENDIX C

### PROCESSING LOG

######## **[Electromagnetics Processing:]{.underline}**

All steps performed on all EM channels unless otherwise stated.

-   Due to a conversion error in the transfer of the raw helicopter data
    file to the field database, the coaxial 3300 Hz data required a
    multiplier of 2. This factor was applied to the coaxial in-phase and
    quadrature channels prior to delivery of the final archives but
    would not have been applied to any of the preliminary data products.

-   Filter raw EM channels 11pt median followed by 11 pt Hanning\
    L400I → CPIR400, L400Q → CPQR400\
    L1K5I → CPIR1500, L1K5Q → CPQR1500\
    L1K7I → CXIR3300, L1K7Q → CXQR3300\
    L6K2I → CPIR6200, L6K2IQ → CPQR6200\
    L25KI → CPIR25K, L25KQ → CPQR25K\
    L100I → CPIR100K, L100Q → CPQR100K

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-   Apply manual leveling picks to filtered EM channels.

-   Gain adjustment for 100 kHz and 25 kHz to correct known errors from
    EM calibration. Gain increase of 18% and 13% applied to the inphase
    and quadrature of the 100 kHz and 25 kHz respectively. These gain
    corrections would not have been applied to any preliminary data
    products.

-   Calculate resistivity and depth channels with Fugro proprietary
    software using filtered and gained EM data.

-   Calculate centroid depths (CEN\*), differential resistivity (DRES\*)
    and differential depths (DRES\*).

-   Filter output channels (RES\*, DEP\*, DRES\*, DDEP\*, CEN\*). 21pt
    median 21pt Hanning. All unfiltered channels are in the archive with
    the suffix \_NF.

-   See the archive CD-ROM or Appendix B for complete channel name
    description.

**[Magnetics Processing (from Russell Imrie)]{.underline}**

MAGSP is the raw channel MAGUR manually despiked using a fourth
difference as a reference. All spikes occurred in areas where the mag
was smoothly varying. This allowed the defaulted areas to be
interpolated using an Akima spline. A 5 point hanning was used to smooth
the transition from areas defaulted and splined to areas not defaulted.
A lag of 11 scans (1.1 seconds) was applied to the mag. DIURNAL data
were examined for spikes and applied to produce the MAGDL channel. MAGDL
and MAGL were gridded and compared to ensure no valid anomalies were
being removed and that the grid was improved by the diurnal application.

IGRF was computed on a point by point basis using the final Z channel as
height above sea level and a year 2000 table of coefficients. May 2002
was the calculation date. Tie line leveling was not used as the altitude
and gradient misties were too great.

A grid based vertical gradient was calculated from the IGRF corrected
mag. It was shadowed and inspected but revealed no leveling errors on
either area.

**[Digital Elevation Model Processing (from Russell
Imrie)]{.underline}**

The barometric altimeter was converted to metres and filtered with an 11
point Hanning. It was profiled and inspected against the Z channel for
spikes. Significant steps were removed and splined or DC shifted to
match the character of the Z trace. The Z data were also inspected in
this manner, compared to the filtered barometric altimeter trace for
sharp changes. Corrections were made by defaulting and splining or by
shifting data so the Z profile matched the character of the Baro.
Altbirdr has been filtered by Mike Cain to produce ALTBIRDM. ALTBIRDM
had a couple of spikes that were removed and splined. ALTLASER was
produced by Mike Cain and severe spikes were removed and splined using
ALTBIRDM as a reference. Some of the ALTLASER data spikes covered areas
where the ALTBIRDM showed rapid variation. These were not splined.

DTM\'s were calculated as follows:

DTMB - BALT-ALTBIRDM

DTMZ - Z-ALTBIRDM

These were contoured, inspected and compared. The tie line leveling
corrections were applied to the BALTF channel to produce the final BALT
channel.

# 

# APPENDIX D

### BACKGROUND INFORMATION

##### D.1 Resistivity Mapping

Areas of widespread conductivity are commonly encountered during
surveys. These conductive zones may reflect alteration zones,
shallow-dipping sulphide or graphite-rich units, saline pools or water
tables, or conductive overburden. In such areas, anomalies can be
generated by decreases of only 5 m in survey altitude as well as by
increases in conductivity. The typical flight record in conductive areas
is characterized by in-phase and quadrature channels which are
continuously active. Local EM peaks reflect either increases in
conductivity of the earth or decreases in survey altitude. For such
conductive areas, apparent resistivity profiles and contour maps are
necessary for the correct interpretation of the airborne data. The
advantage of the resistivity parameter is that anomalies caused by minor
altitude changes are virtually eliminated, so the resistivity data
reflect only those anomalies caused by conductivity changes. The
resistivity analysis also helps the interpreter to differentiate between
conductive bedrock and conductive overburden. For example, discrete
conductors will generally appear as narrow lows on the contour map and
broad conductors (e.g., overburden, tailings ponds leaks or saline water
tables) will appear as wide lows.

The apparent resistivity is calculated using the pseudo-layer (or
buried) half-space model defined by Fraser (1978)[^5]. This model
consists of a resistive layer overlying a conductive half-space. The
depth channels give the apparent depth below surface of the conductive
material. The apparent depth is simply the apparent thickness of the
overlying resistive layer. The apparent depth (or thickness) parameter
will be positive when the upper layer is more resistive than the
underlying material, in which case the apparent depth may be quite close
to the true depth.

The apparent depth will be negative when the upper layer is more
conductive than the underlying material, and will be zero when a
homogeneous half-space exists. The apparent depth parameter must be
interpreted cautiously because it will contain any errors which may
exist in the measured altitude of the EM bird (e.g., as caused by a
dense tree cover). The inputs to the conductivity algorithm are the
in-phase and quadrature components of the coplanar coil-pair. The
outputs are the apparent conductivity of the conductive half-space (the
source) and the sensor-source distance. The flying height is not an
input variable, and the output conductivity and sensor-source distance
are independent of the flying height when the conductivity of the
measured material is sufficient to yield significant in-phase as well as
quadrature responses. The apparent depth, discussed above, is simply the
sensor-source distance minus the measured altitude or flying height.
Consequently, errors in the measured altitude will affect the apparent
depth parameter but not the apparent conductivity parameter.

The apparent depth parameter is a useful indicator of simple layering in
areas lacking a heavy tree cover. The DIGHEM system has been flown for
purposes of permafrost mapping, where positive apparent depths were used
as a measure of permafrost thickness. However, little quantitative use
has been made of negative apparent depths because the absolute value of
the negative depth is not a measure of the thickness of the conductive
upper layer and, therefore, is not meaningful physically. Qualitatively,
a negative apparent depth estimate usually shows that the EM anomaly is
caused by a conductive layer at surface. Consequently, the apparent
depth channel can be of significant help in distinguishing between
overburden and bedrock conductors.

The DP channels, which give the apparent depth to the conductive
material, also help to determine whether a conductive response arises
from surficial material or from a conductive zone in the bedrock. When
these channels ride above the zero level on the digital profiles (i.e.,
depth is negative), it implies that the EM and conductivity profiles are
responding primarily to a conductive upper layer, i.e., conductive
overburden. If the DP channels are below the zero level, it indicates
that a resistive upper layer exists, and this usually implies the
existence of a bedrock conductor. If the low frequency DP channel is
below the zero level and the high frequency DP is above, this suggests
that a bedrock conductor occurs beneath conductive cover.

##### D.2 Reduction of Geologic Noise

Geologic noise refers to unwanted geophysical responses. For purposes of
airborne EM surveying, geologic noise refers to EM responses caused by
conductive overburden and magnetic permeability.

Magnetite produces a form of geological noise on the in-phase channels
of all EM systems. Rocks containing less than 1 % magnetite can yield
negative in-phase anomalies caused by magnetic permeability. When
magnetite is widely distributed throughout a survey area, the in-phase
EM channels may continuously rise and fall, reflecting variations in the
magnetite percentage, flying height, and overburden thickness. This can
lead to difficulties in recognizing deeply buried bedrock conductors,
particularly if conductive overburden also exists.

##### D.3 Magnetics

Total field magnetics provides information on the magnetic properties of
the earth materials in the survey area. The information can be used to
locate magnetic bodies of direct interest for exploration, and for
structural and lithological mapping.

The total field magnetic response reflects the abundance of magnetic
material, in the source. Magnetite is the most common magnetic mineral.
Other minerals such as ilmenite, pyrrhotite, franklinite, chromite,
hematite, arsenopyrite, limonite and pyrite are also magnetic, but to a
lesser extent than magnetite on average.

In some geological environments, an EM anomaly with magnetic correlation
has a greater likelihood of being produced by sulphides than one which
is non-magnetic. However, sulphide ore bodies may be non-magnetic (e.g.,
the Kidd Creek deposit near Timmins, Canada) as well as magnetic (e.g.,
the Mattabi deposit near Sturgeon Lake, Canada).

Iron ore deposits will be anomalously magnetic in comparison to
surrounding rock due to the concentration of iron minerals such as
magnetite, ilmenite and hematite.

Changes in magnetic susceptibility often allow rock units to be
differentiated based on the total field magnetic response. Geophysical
classifications may differ from geological classifications if various
magnetite levels exist within one general geological classification.
Geometric considerations of the source such as shape, dip and depth,
inclination of the earth\'s field and remanent magnetization will
complicate such an analysis.

In general, mafic lithologies contain more magnetite and are therefore
more magnetic than many sediments which tend to be weakly magnetic.
Metamorphism and alteration can also increase or decrease the
magnetization of a rock unit.

Textural differences on a total field magnetic contour, colour or shadow
map, due to the frequency of activity of the magnetic parameter
resulting from inhomogeneities in the distribution of magnetite within
the rock, may define certain lithologies. For example, near surface
volcanics may display highly complex contour patterns with little
line-to-line correlation.

Rock units may be differentiated based on the plan shapes of their total
field magnetic responses. Mafic intrusive plugs can appear as isolated
\"bulls-eye\" anomalies. Granitic intrusives appear as sub-circular
zones, and may have contrasting rings due to contact metamorphism.
Generally, granitic terrain will lack a pronounced strike direction,
although granite gneiss may display strike.

Linear north-south units are theoretically not well-defined on total
field magnetic maps in equatorial regions due to the low inclination of
the earth\'s magnetic field. However, most stratigraphic units will have
variations in composition along strike which will cause the units to
appear as a series of alternating magnetic highs and lows.

Faults and shear zones may be characterized by alteration which causes
destruction of magnetite (e.g., weathering) which produces a contrast
with surrounding rock. Structural breaks may be filled by
magnetite-rich, fracture filling material as is the case with diabase
dikes, or by non-magnetic felsic material.

Faulting can also be identified by patterns in the magnetic total field
contours or colours. Faults and dikes tend to appear as lineaments and
often have strike lengths of several kilometres. Offsets in narrow,
magnetic, stratigraphic trends also delineate structure. Sharp contrasts
in magnetic lithologies may arise due to large displacements along
strike-slip or dip-slip faults.

# APPENDIX E 

FLIGHT LOGS

# 

# APPENDIX F

**TESTS AND CALIBRATIONS**

**EM Calibrations**

# CALIBRATION OF THE DIGHEM DIGITAL (DSP) SYSTEM

The calibration method used in the digital Dighem^V^ has been developed
as a significant improvement over the practices described by Fitterman
(1998), which practices were originally developed through
experimentation and consultation between Fugro and the United States
Geological Survey. The problems defined by Fitterman, including jig
calibration and conductive ground response, are obviated by calibration
at high altitude using internal, rigidly mounted, automatically
triggered and measured calibration coils.

Calibration of the system during the survey will use the Fugro AutoCal™
automatic, internal calibration process. At the beginning and end of
each flight, and at intervals during the flight, the system will be
flown up to high altitude to remove it from any "ground effect"
(response from the earth). Any remaining signal from the receiver coils
(base level) will be measured as the zero level, and removed from the
data collected until the time of the next calibration. Following the
zero level setting, internal calibration coils, for which the response
phase and amplitude have been determined at the factory, are
automatically triggered -- one for each frequency. The on-time of the
coils is sufficient to determine an accurate response through any
ambient noise. The receiver response to each calibration coil "event" is
compared to the expected response (from the factory calibration) for
both phase angle and amplitude, and the applied phase and gain
corrections adjusted to bring the data to the correct value.

In addition, the output of the transmitter coils are continuously
monitored during the survey, and the applied gains adjusted to correct
for any change in transmitter output (due to heating, etc.)

Because the internal calibration coils are calibrated at the factory (on
a resistive halfspace) ground calibrations using external calibration
coils on-site are not necessary for system calibration. A check
calibration may be carried out on-site to ensure all systems are working
correctly. All system calibrations will be carried out in the air, at
sufficient altitude that there will be no measurable response from the
ground.

The internal calibration coils are rigidly positioned and mounted in the
system relative to the transmitter and receiver coils. In addition, when
the internal calibration coils are calibrated at the factory, a rigid
jig is employed to ensure accurate response from the external coils.

Using real time Fast Fourier Transforms and the calibration procedures
outlined above, the data will be processed in real time from measured
total field at a high sampling rate to in-phase and quadrature values at
10 samples per second.

Greg Hodges, Chief Geophysicist 01/04/09

References:

Fitterman, D.V., (1998). Sources of calibration errors in helicopter EM
data. Exploration Geophysics 29, 65-70.

**[External Calibration Results]{.underline}**

  --------------- --------------- -------------- ------------ -------------- ------------ -----------
                                                                                          

  May 21, 2002    Start                                                                   
                  calibrations.                                                           
                  In Seco Creek                                                           
                  survey area                                                             

                                                                                           

  **FREQUENCY**   **CHANNEL**     **INTERNAL**                **EXTERNAL**                **PHASE**

                                  **MEASURED**   **TARGET**   **MEASURED**   **TARGET**   

  400             L400I           207.0          200.0        208.0          200.4        -233.0

                  L400Q           204.0          200.0        200.0          200.4        -9.0

  1500            L1K5I           185.0          183.0        199.0          204.2        -175.0

                  L1K5Q           180.0          183.0        189.0          204.2        6.0

  3300            L1K7I           93.0           94.0         88.0           99.9         -259.0

                  L1K7Q           92.0           94.0         89.0           99.9         -4.0

  6200            L6K2I           830.0          822.0        186.0          207.5        -414.0

                  L6K2Q           827.0          822.0        195.0          207.5        -10.0

  25000           L25KI           404.0          409.0        132.0          192.5        -1695.0

                  L25KQ           398.0          409.0        155.0          192.5        -76.0

  100000          L100I           310.0          320.0        80.0           178.8        -4430.0

                  L100Q           319.0          320.0        92.0           178.8        -322.0

                                                                                          

  May 27, 2002    End                                                                     
                  calibrations.                                                           
                  In Seco Creek                                                           
                  survey area                                                             

                                                                                          

  **FREQUENCY**   **CHANNEL**     **INTERNAL**                **EXTERNAL**                **PHASE**

                                  **MEASURED**   **TARGET**   **MEASURED**   **TARGET**   

  400             L400I           206.0          200.0        210.0          200.4        -225.0

                  L400Q           204.0          200.0        202.0          200.4        -9.0

  1500            L1K5I           182.0          183.0        199.0          204.2        -261.0

                  L1K5Q           180.0          183.0        192.0          204.2        3.0

  3300            L1K7I           92.0           94.0         87.0           99.9         -273.0

                  L1K7Q           94.0           94.0         88.0           99.9         -5.0

  6200            L6K2I           824.0          822.0        187.0          207.5        -439.0

                  L6K2Q           826.0          822.0        198.0          207.5        -12.0

  25000           L25KI           402.0          409.0        131.0          192.5        -1661.0

                  L25KQ           402.0          409.0        156.0          192.5        -60.0

  100000          L100I           311.0          320.0        \*             178.8        -3724.0

                  L100Q           311.0          320.0        \*             178.8        -201.0

                                                                                          

  \* excessive                                                                            
  noise could not                                                                         
  determine data                                                                          
  values                                                                                  

                                                                                          

                                                                                          

                                                                                          

                                                                                          

  June 6, 2002    Mountsberg                                                              
                  calibration                                                             
                  site, Milton,                                                           
                  Ontario                                                                 

                                                                                           

  **FREQUENCY**   **CHANNEL**     **INTERNAL**                **EXTERNAL**                **PHASE**

  ** **           ** **           **MEASURED**   **TARGET**   **MEASURED**   **TARGET**   ** **

  400             L400I           203.0          200.0        209.2          200.4        -238.0

                  L400Q           202.8          200.0        203.5          200.4        -12.0

  1500            L1K5I           182.2          183.0        200.0          204.2        -250.0

                  L1K5Q           181.9          183.0        193.0          204.2        3.5

  3300            L1K7I           94.5           94.0         88.0           99.9         -222.0

                  L1K7Q           93.9           94.0         88.0           99.9         -3.0

  6200            L6K2I           825.0          822.0        189.3          207.5        -456.0

                  L6K2Q           824.0          822.0        198.3          207.5        -7.0

  25000           L25KI           419.8          409.0        142.3          192.5        -1950.0

                  L25KQ           407.4          409.0        156.7          192.5        3.0

  100000          L100I           316.3          320.0        79.0           178.8        -1479.0

                  L100Q           321.0          320.0        80.0           178.8        16.0
  --------------- --------------- -------------- ------------ -------------- ------------ -----------

**Notes:**

-   Differences in the "measured" and "target" values in the external
    calibrations are corrected using scaling factors in the DSP
    software. The important numbers in the calibration tables above are
    the "measured" and "target" values in the internal calibrations.
    These offsets can also be monitored during flight using digital data
    from the "turns" in the database.

-   No changes were made during these calibrations. The final
    calibration from Mountsberg on June 6 represents how the system was
    calibrated during the survey.

# 

######### 

[^1]: Sengpiel, K.P., 1988, imate Inversion of Airborne EM Data from
    Multilayered Ground: Geophysical Prospecting 36, 446-459.

[^2]: Huang, H. and Fraser, D.C., 1993, Differential Resistivity Method
    for Multi-frequency Airborne EM Sounding: presented at Intern. Airb.
    EM Workshop, Tucson, Ariz.

[^3]: Constable et al, 1987, Occam's inversion: a practical algorithm
    for generating smooth models from electromagnetic sounding data:
    Geophysics, 52, 289-300.

[^4]: Huang H., and Palacky, G.J., 1991, Damped least-squares inversion
    of time domain airborne EM data based on singular value
    decomposition: Geophysical Prospecting, 39, 827-844.

[^5]: ^?^ Resistivity mapping with an airborne multicoil electromagnetic
    system: Geophysics, v. 43, p.144-172