

                         Logistics
                          Report

                          for a

         High Resolution Fixed Wing Magnetic Survey

                            of 

            Portions of the States of Wisconsin,
                Minnesota, Michigan and Iowa

                 carried out on behalf of

                  U.S. Geological Survey
                     Denver, Colorado

                            by

               High-Sense Geophysics Limited



                      Toronto, Canada
                         July 1999
                         (980825-1)



TABLE OF CONTENTS



1.      INTRODUCTION...................................1
2.      LOCATION.......................................1
         Location Map:  Wisconsin Project Area.........4
3.      AIRCRAFT AND EQUIPMENT.........................5
3.1      Aircraft......................................5
3.2      Airborne Geophysical System...................5
3.2.1      Magnetometer................................5
3.2.2      Magnetic Compensation.......................5
3.2.3      GPS Navigation..............................5
3.2.4      Altimeter...................................5
3.2.5      Geophysical Flight Control System...........6
3.2.6      Digital Recording...........................6
3.3      Ground Monitoring System......................6
3.3.1      Magnetometer................................6
3.3.2      GPS Monitor.................................6
3.3.3      Recording...................................6
3.4      Field Compilation System......................7
4.      PERSONNEL......................................7
4.1      Field Operations..............................7
4.2      Project Management............................7
5.      SURVEY PARAMETERS..............................7
6.      OPERATIONS AND PROCEDURES......................8
6.1      Flight Planning...............................8
6.2      Base Station..................................8
6.3      Data Compilation..............................9
6.3.1      Flight Path Correction......................9
6.3.2      Magnetic Corrections.......................10
6.3.3      Map Products and Digital Data..............10
APPENDIX A Figure-of-Merit.............................i



1.        INTRODUCTION

In September 1998, High-Sense Geophysics Limited was contracted
by the United States Geological Survey to provide a fixed wing
magnetic survey over an area of interest located primarily in the
southern half of Wisconsin, and portions of Minnesota, Michigan
and Iowa.

The survey was flown between September 15, 1998 and February 21,
1999.  A total of 74015 line-kilometers of total field magnetic
data, flown at a nominal line spacing of 800 metres, was
collected, processed and plotted on-site. 

The technical objective of the survey was to provide high
resolution magnetic maps, suited for anomaly delineation,
detailed structural evaluation and identification of lithologic
trends.  Fully corrected magnetic maps were prepared by
High-Sense's Toronto office after completion of survey
activities. 



2.        LOCATION


Latitude and longitude coordinates, central meridian and zone
used to define the blocks are listed below - see accompanying map
for relative locations. 


Central meridian: 87 W, UTM Zone: 16

Area 1
Corner No.      Latitude     Longitude   
     1          43:30:00 N   91:20:00 W
     2          43:48:00 N   91:22:30 W
     3          44:00:00 N   91:33:30 W
     4          44:02:30 N   91:39:00 W
     5          44:02:30 N   90:51:00 W
     6          44:15:00 N   90:51:00 W
     7          44:15:00 N   90:18:00 W
     8          44:26:00 N   90:18:00 W
     9          44:26:00 N   90:02:30 W
    10          44:00:00 N   90:02:30 W
    11          44:00:00 N   90:00:00 W
    12          43:30:00 N   90:00:00 W

Area 2
Corner No.      Latitude     Longitude   
     1          43:00:00 N   91:12:30 W
     2          43:17:30 N   91:13:30 W
     3          43:30:00 N   91:20:00 W
     4          43:30:00 N   90:00:00 W
     5          43:00:00 N   90:00:00 W

Area 3
Corner No.      Latitude     Longitude   
     1          43:30:00 N   90:00:00 W
     2          44:02:30 N   90:00:00 W
     3          44:02:30 N   88:47:30 W
     4          44:00:00 N   88:47:30 W
     5          44:00:00 N   88:15:00 W
     6          43:45:00 N   88:15:00 W
     7          43:45:00 N   88:45:00 W
     8          43:30:00 N   88:45:00 W

Area 4
Corner No.      Latitude     Longitude   
     1          44:00:00 N   88:47:30 W
     2          44:32:30 N   88:47:30 W
     3          44:32:30 N   87:22:30 W
     4          44:00:00 N   87:22:30 W

Area 5
Corner No.      Latitude     Longitude   
     1          44:32:30 N   87:40:00 W
     2          45:09:00 N   87:40:00 W
     3          45:52:30 N   87:05:00 W
     4          45:52:30 N   86:45:00 W
     5          45:15:00 N   86:45:00 W
     6          44:32:30 N   87:22:30 W

Area A
Corner No.      Latitude     Longitude   
     1          42:29:30 N   90:29:00 W
     2          42:29:30 N   90:39:30 W
     3          42:37:30 N   90:43:30 W
     4          42:40:30 N   91:00:00 W
     5          42:45:00 N   91:06:00 W
     6          42:52:30 N   91:07:30 W
     7          42:55:00 N   91:10:15 W
     8          43:00:00 N   91:12:30 W
     9          43:00:00 N   90:29:00 W

Area B
Corner No.      Latitude     Longitude   
     1          44:00:00 N   87:52:30 W
     2          44:00:00 N   87:35:19 W
     3          43:45:00 N   87:36:16 W
     4          43:22:30 N   87:46:19 W
     5          43:09:34 N   87:47:28 W
     6          43:09:34 N   88:11:23 W
     7          43:22:30 N   88:11:23 W
     8          43:29:02 N   88:40:49 W
     9          43:36:53 N   88:40:49 W
    10          43:36:53 N   88:19:56 W

Area C
Corner No.      Latitude     Longitude   
     1          43:09:38 N   88:11:23 W
     2          43:09:38 N   87:47:28 W
     3          42:54:30 N   87:46:07 W
     4          42:47:12 N   87:41:40 W
     5          42:40:52 N   87:41:40 W
     6          42:37:30 N   87:43:00 W
     7          42:29:18 N   87:43:00 W
     8          42:29:18 N   88:27:47 W
     9          42:32:45 N   88:27:47 W
    10          42:32:45 N   87:55:22 W
    11          42:43:45 N   87:55:22 W
    12          42:43:45 N   88:27:47 W
    13          42:50:05 N   88:27:47 W
    14          42:50:05 N   88:15:08 W

Area D
Corner No.      Latitude     Longitude   
     1          43:30:00 N   88:58:42 W
     2          43:13:29 N   88:58:42 W
     3          43:13:29 N   88:50:26 W
     4          42:55:36 N   88:50:26 W
     5          42:50:05 N   88:27:47 W
     6          42:29:30 N   88:27:47 W
     7          42:29:30 N   89:02:30 W
     8          43:30:00 N   89:02:30 W

Area E
Corner No.      Latitude     Longitude   
     1          42:29:30 N   90:08:30 W
     2          43:00:00 N   90:08:30 W
     3          43:00:00 N   90:00:00 W
     4          43:30:00 N   90:00:00 W
     5          43:30:00 N   89:02:30 W
     6          42:29:30 N   89:02:30 W



Location Map:  Wisconsin Project Area



3.        AIRCRAFT AND EQUIPMENT


3.1        Aircraft

The aircraft used was a Cessna 206 fixed wing (C-GNNN) owned and
operated by Bruceland Air of Wiarton, Ontario.


3.2        Airborne Geophysical System
3.2.1        Magnetometer

One Geometrics G-8 22A Optically Pumped Cesium Split Beam Sensor
was mounted in a fixed wing pod at the end of the wind.  The
Larmor frequency output was processed by a High-Sense
magnetometer counter that provides a resolution of  10 ppb (in a
magnetic field of 50,000 nT this resolution is equivalent to
0.005 nT) ten times per second.


3.2.2        Magnetic Compensation

A Billingsley Magnetics TFM100-1E three axis fluxgate
magnetometer measured the orientation and rates of change of the
aircraft's magnetic field with respect to the Earth's magnetic
field.  Correction factors were then generated to compensate for
permanent, induced and eddy current magnetic anomalies generated
by the aircraft.


3.2.3        GPS Navigation

A Novatel 951 twelve channel GPS receiver, which is an integral
component of the HS-GFCS-II flight control system, provided
precise positioning.


3.2.4        Altimeter

A Terra TRA 3000 radar altimeter was mounted on the aircraft.
This instrument operates with a linear performance over the range
of 20 to 1500 metres, and records the terrain clearance of  the
magnetic sensor.

A Rosemount barometric altimeter was also mounted on the
aircraft.  This instrument operates with a linear performance
over the range of -1000 to 15000 feet.


3.2.5        Geophysical Flight Control System

The High-Sense MiniMag Data Acquisition flight control system
monitored and recorded magnetometer, altimeter and GPS equipment.
Input from the various sensors was monitored every 0.005 seconds
for precise coordination of geophysical and positional
measurements.  GPS positional coordinates and terrain clearance
were presented to the pilot by means of an LCD touch screen
display.  The magnetometer response, 4th difference, and
altimeter profile were also shown on the LCD touch screen display
for real time monitoring of equipment performance.


3.2.6        Digital Recording

The output of the magnetometer, compensation equipment and
altimeter as well as uncorrected GPS coordinates were recorded
digitally on disk at a sample rate of ten times per second by the
HSG MiniMag Data Acquisition system.  Line number, GPS time and
system time were also recorded for use during subsequent
differential GPS correction.



3.3        Ground Monitoring System
3.3.1        Magnetometer

A Scintrex H-8 magnetometer was operated as a base station to
record diurnal variations of the Earth's magnetic field.
Readings with a resolution of  0.1 nT were recorded digitally
every second, and synchronized with GPS time for accurate
correction of the airborne data.


3.3.2        GPS Monitor

A Magnavox 9200 twelve channel receiver with a fixed antenna was
also active at the base of operations.  Raw satellite data was
digitally recorded to enable differential correction of  the
corresponding airborne data.


3.3.3        Recording

The output of the magnetic and GPS monitors was recorded
digitally on a dedicated  PC.  A visual record of the last four
hours of activity is graphically maintained on the computer
screen to provide an up to date appraisal of magnetic activity.
At the conclusion of each production flight raw GPS and magnetic
data were transferred to the main compilation computer.



3.4        Field Compilation System

A Pentium PC computer and a Hewlett Packard Design Jet 350C
colour plotter were used for field data processing and
presentation.  Processing software and procedures were developed
by High-Sense Geophysics Limited, and include the Geopak RTICAD
imaging system.



4.        PERSONNEL


4.1        Field Operations

USGS Representative           : Robert E. Bracken
High-Sense data processors    : Amir Soltanzadeh
                                Steven Green
                                Darrick Wagg
Bruceland pilots              : Will Plageman
                                Tom Martindale
Bruceland Engineer            : Tom Elmes


4.2        Project Management
        
USGS, Denver office           : Robert E. Bracken
High-Sense, Toronto office    : Ted Urquhart

5.        SURVEY PARAMETERS

Traverse Line spacing         : 800 metres
Control Line spacing          : 12,500 metres 
Nominal Terrain clearance     : 1000 feet
Navigation                    : Global Positioning System
Traverse Line direction       : North-South,
                                   (East West for Area C)
Control Line direction        : East-West,
                                   (North-South for Area C)
Measurement interval          : 0.1 sec
Airspeed (nominal)            : 210 km/hr 
Measurement spacing (nominal) : 6.0 meters
Airborne Digital Record       : Radar Altimeter
                                Barometric Altimeter        
                                Total Field Magnetics
                                Time (Local and GPS)
                                Raw Global Positioning System
                                   (GPS) data
                                Magnetic compensation parameters
Base Station Record           : Ambient Total Field Magnetics
                                Raw Global Positioning System
                                   (GPS) data
                                Time (Local and GPS)



6.        OPERATIONS AND PROCEDURES


6.1        Flight Planning

Survey block outlines were specified by USGS (section 2.0), and
the coordinates used to generate pre-calculated navigation files.
These, in turn, were used by the airborne data acquisition system
to plan flights at the designated line spacing of 800 metres.


6.2        Base Station

The GPS and magnetic base station site was established at various
locations close to the base of operations for each particular
area.  A total of four locations were used during the course of
the survey.  A description and exact position of the locations is
listed below: 


1. Green Bay Wisconsin:  The base station was set up in a remote
section of the airport.

44:29:41.98 N          174.6 m asl
88:07:50.12 W          (Clarke 1866 spheroid)

2. Manitouwoc Wisconsin:  The base station was set up in a remote
section of the airport.

44:07:19.6176 N        168.4 m asl
87:41:03.1164 W        (Clarke 1866 spheroid)

3. Platteville Wisconsin:  The base station was set up in a
remote section of the airport.

42:41:30.5797 N        278.5 m asl
90:26:24.8613 W        (Clarke 1866 spheroid)

4. Janesville Wisconsin:  The base station was set up in a remote
section of the airport.

42:36:40.1443 N        203.38 m asl
89:02:44.1223 W        (Clarke 1866 spheroid)


The GPS antenna should be located at an accurately surveyed
position point, since positional errors are carried through to
the differentially corrected data.  Because no suitable control
point was available, the location of the GPS antenna was
determined by recording 24 hours of GPS data and averaging the
resultant antenna coordinates (the assumption being that the
deliberate errors introduced by military selective availability
satellite signal distortion will average to zero over an extended
period of time).

6.3        Data Compilation

Data recorded by the airborne and base station systems was
transferred to the field compilation system.  As each flight was
completed, the following compilation operations were carried out. 


6.3.1        Flight Path Correction

The GPS data was differentially corrected to remove errors
introduced by 'selective availability', an intentional accuracy
degradation method used by the military.  The correction process
uses the known fixed location of the base station to calculate
the error associated with each satellite.  These errors are then
removed from the survey GPS data enabling a position to be
calculated with an accuracy in the order of three metres, with
four or more satellites in view.  Satellite visibility and
coverage were good throughout field operations.  Both GPS
receivers were generally tracking a minimum of seven satellites.

The navigational correction process yields a flight path
expressed in WGS 84 Latitude-Longitude coordinates.
Transformation to local Clarke 1866 (NAD 27) UTM coordinates used
the following projection parameters :

        Semi-major axis (a)                  Flattening (f)

WGS 84          6378137.0                         298.2572201
Clarke 1866     6378206.4                         294.9786982
  (NAD 27)

Local datum shift applied :

        Delta X        :             9
        Delta Y        :          -160
        Delta Z        :          -176

UTM central meridian   =    87 W (Zone 16)

        False Easting                :    500,000
        False Northing               :          0



6.3.2        Magnetic Corrections

Diurnal variations recorded by the base station were subtracted
directly from the aeromagnetic measurements to provide a first
order diurnal correction.  Aeromagnetic data was compensated for
permanent, induced and eddy current magnetic noise generated by
the aircraft.  Figure of Merit tests were conducted at the
beginning of the survey and after each time the orientation of
the magnetometer was adjusted (See Appendix A for details).
 
Control lines flown perpendicular to the traverse lines were used
to provide level correction.  Residual differences between
control and traverse lines were used to carry out a further
refinement of diurnal and heading errors.   Micro leveling
technique was also used to correct any problems not removed by
tie line leveling.  Any apparent cultural effects noted in the
magnetic maps were not removed from either preliminary or final
map products.


6.3.3        Map Products and Digital Data

Interim digital data for the blocks were supplied to USGS as the
survey progressed.  Following processing in the High-Sense
Toronto office, copies of the final map products (see below),
plus three (2) copies of the digital data (CD-ROM), video
cassettes used to assist in tracking the aircraft, and this
logistics report were delivered to USGS.

1. Maps at 1:100,000 of the Total Magnetic Field with contours,
flight path in triplicate on clear mylar.

2. Maps at 1:100,000 of the radar altimeter with contours, flight
path on clear overlay (mylar) in single copy.



Respectfully submitted,

                   Steven Green, E.I.T.
                   High-Sense Geophysics Limited
                   August 25, 1998



APPENDIX A:    Figure-of-Merit

Magnetic Figure-Of-Merit Tests

The airborne magnetic record is corrected using an 18 term
post-flight digital compensation system that uses magnetic data
from the Barrington 3-axis fluxgate magnetometer to determine the
aircraft's attitude and rate of change with respect to the
earth's magnetic field.  The compensation system identifies the
permanent, induced and eddy current magnetic contributions of the
aircraft and provides a correction to be applied to the raw
magnetic data to remove maneuver noise.

In order to calibrate the compensation system, tests are flown at
high altitude to determine the effects of aircraft pitch, roll
and yaw.  The aircraft flies each of the headings aligned with
the direction of the survey flight lines and control lines,
performing three sets of pitch roll and yaw maneuvers over
periods of approximately six, ten and fourteen seconds.  The data
is subsequently used to calibrate the compensation
system.

The following figures show the results (raw and compensated
magnetic signature) of three Figure-Of-Merit tests:


September 20 FOM Results (North: line 4027, South: line 4022)
September 20 - 1.18

December 18 FOM Results (East: line 3016, West: line 3013)
December 18  - 1.37

February 20 FOM Results (North: line 20, South: line 40)
February 20  - 1.22

