**FINAL REPORT**

on

**Data Acquisition and Processing**

for the

**Airborne Magnetic Survey**

of

**The Excelsior Mountains and South Wassuk Range of Western Nevada**

on behalf of the

**United States Geological Survey**

Brian Schacht P. Geoph.

Ottawa, Ontario, Canada

March, 2001

**TABLE OF CONTENTS**

**1. INTRODUCTION 2**

**2. TECHNICAL SPECIFICATIONS 3**

1.  SURVEY LOCATION 3

2.  FLIGHT SPECIFICATIONS 3

2.3 TOLERANCES 3

2.4 SURVEY EQUIPMENT 4

**3. PERSONNEL 5**

**4. SURVEY OPERATIONS 6**

4.1 GENERAL 6

4.2 DIURNAL CONDITIONS 6

4.3 GENERAL WEATHER CONDITIONS 6

4.4 QUALITY CONTROL AND FIELD PROCESSING 6

**5. CALIBRATION AND TEST RESULTS 7**

5.1 GPS BASE STATION 7

5.2 MAGNETIC LAG TEST 7

5.3 GPS LAG / ACCURACY TEST 8

5.4 FIGURE OF MERIT 10

5.  ALTIMETER CALIBRATION 10

**6. FINAL MAGNETIC DATA PROCESSING 11**

6.1 NOISE EDITING 11

6.2 NOISE FILTERING 11

6.3 DIURNAL SUBTRACTION 12

6.4 IGRF CORRECTION 12

6.5 UPWARD/DOWNWARD CONTINUATION 12

6.6 LEVELLING 12

6.7 GRIDDING 13

6.8 GRID LEVELLING 13

**7. DELIVERABLES 14**

1.  MAPS 14

7.2 REPORT 14

7.3 DIGITAL ARCHIVES 14

######## APPENDIX: DIGITAL ARCHIVE FORMAT DESCRIPTION 15 

**1. INTRODUCTION**

An aeromagnetic survey was flown over three conjoined areas within the
Excelsior Mountains and Southern Wassuk Range of western Nevada. This
same survey covered part of Death Valley, California. The flying was
completed between December 5, 2000, and January 14, 2001, by Fugro
Airborne Surveys on behalf of the United States Geological Survey (see
figure 1). A 1:100,000 scale contour map and digital grid of the total
magnetic field were produced, as well as a digital grid of radar
altimeter (ground clearance) data.

![](media/image1.wmf)

**2. TECHNICAL SPECIFICATIONS**

This section describes in detail the guidelines followed throughout the
performance of the project; tolerances and instruments are also
presented here.

1.  SURVEY LOCATION

The three conjoined western Nevada areas (1, 2, & 4) are bounded by the
following co-ordinates (NAD27 UTM and degrees X 1,000,000):

404000.00 4255000.00 38262393 -118055996

409100.00 4237100.00 38164519 -118022131

412000.00 4237100.00 38164623 -118002197

412000.00 4212600.00 38033142 -118001106

361100.00 4212600.00 38030844 -118345912

361100.00 4248600.00 38223605 -118352448

340200.00 4248600.00 38222349 -118494545

331300.00 4259700.00 38281754 -118560163

331300.00 4264500.00 38305318 -118560580

347200.00 4264500.00 38310352 -118450957

356400.00 4255000.00 38260094 -118384281

2.2 FLIGHT SPECIFICATIONS

Traverse Line Direction N - S

Traverse Line Spacing 250 m

Control Line Direction E - W

Control Line Spacing 1,500 m

Terrain Clearance 168-1217 m+ - see section 2.3 - "Flying Height".

Line kilometers: 11,259.77

Average Sampling Interval 7.5 m

2.3 TOLERANCES

Lines (or segments of lines crossing two control lines, or segments of
control lines crossing several lines) were re-flown when any of the
following tolerances were exceeded:

[Navigation]{.underline}

-   Nominal line spacing must not be exceeded by more than 50% for a
    distance of more than 3.2 km.

######### Flight Height

-   In order to maintain similar elevations at all traverse and control
    line intersections, even when climbing or descending steeply, the
    Fugro *ACCUDRAPE* system utilizes a pre-planned digital drape
    surface which the onboard computer compares with the GPS xyz to feed
    corrections to the pilot.

-   Deviations from the pre-planned drape elevation must not exceed
    100 m. The precipitous mountains flanking all survey blocks
    necessitated pre-planned drape surfaces with ground clearance
    exceeding 1217 m (4000') over the valleys (the radar altimeter
    maximum is 1217 m). Less than 1% of the data could be flown below
    213 m (700').

######### Magnetic Diurnal

-   Deviations must not be greater than 2 nT from a 40 second chord. The
    ground station magnetometer operated during all data acquisition.

    [Airborne Magnetometer Noise]{.underline}

```{=html}
<!-- -->
```
-   "Maneuver" noise must not exceed an envelope of ±0.1 nT over more
    than 10% of any line. This was monitored on the analog chart with a
    fourth difference and a high-pass filter.

```{=html}
<!-- -->
```
-   A standard Figure of Merit must be less than 1.5 nT.

-   Heading errors must be within 1 nT between reciprocal headings.

    2.4 SURVEY EQUIPMENT

    Table 2.4.a lists major characteristics of the fixed-wing survey
    aircraft.

+----------+---------+--------+-----------+---------+------+--------+
| **Regist | **Endu  | **Eng  | **Manuf   | *       | *    | **Ave  |
| ration** | rance** | ines** | acturer** | *Type** | *No. | rage** |
|          |         |        |           |         | of   |        |
|          |         |        |           |         | Sea  | **S    |
|          |         |        |           |         | ts** | peed** |
+----------+---------+--------+-----------+---------+------+--------+
| **       | 6.5     | 1      | Cessna    | Caravan | 3    | 75     |
| C-FZLK** | hours   |        |           | 208     |      | m/sec  |
|          |         | T      |           |         |      |        |
|          |         | urbine |           |         |      |        |
+----------+---------+--------+-----------+---------+------+--------+

##  Table 2.4.a Survey Aircraft

Table 2.4.b lists the geophysical equipment installed in C-FZLK
throughout the survey.

+--------------+--------------+-----------+---------------------------+
| *            | **Ma         | **Model** | **Type**                  |
| *Equipment** | nufacturer** |           |                           |
+--------------+--------------+-----------+---------------------------+
| Data         | Fugro        | GeoDAS    | Pentium computer based,   |
| Acquisition  | Airborne     |           | real-time,                |
| System       | Surveys      |           |                           |
|              |              |           | data synchronization and  |
|              |              |           | recording                 |
+--------------+--------------+-----------+---------------------------+
| Magnetometer | Scintrex     | CS-2      | Cesium Vapour,10 Hz       |
|              |              |           | Sampling,                 |
|              |              |           |                           |
|              |              |           | 0.005 nT                  |
|              |              |           | Sensitivity,0.001 nT      |
|              |              |           | Resolution                |
+--------------+--------------+-----------+---------------------------+
| Compensator  | RMS          | AADC      | 27 Term                   |
+--------------+--------------+-----------+---------------------------+
| Digital      | Iomega       | Zip Drive | 100 Mb removable hard     |
| Backup       |              |           | drive                     |
+--------------+--------------+-----------+---------------------------+
| Analogue     | RMS          | GR-33a-1  | Dot Matrix                |
| Recorder     |              |           |                           |
+--------------+--------------+-----------+---------------------------+
| Radar        | TRT          | AVH-8     | 10 Hz Sampling, Accuracy  |
| Altimeter    |              |           | ±2%                       |
+--------------+--------------+-----------+---------------------------+
| Barometric   | Rosemount    | 1241M     | 10 Hz Sampling, Accuracy  |
| Altimeter    |              |           | ±5 m                      |
+--------------+--------------+-----------+---------------------------+
| Omnistar     | Trimble      |           | Real-time differential    |
| Receiver     |              |           | GPS correction            |
+--------------+--------------+-----------+---------------------------+
| GPS Receiver | Sercel       | NR103     | 10 Channel                |
+--------------+--------------+-----------+---------------------------+
| Video Camera | Panasonic    | WVC 1302  | Colour                    |
+--------------+--------------+-----------+---------------------------+
| Video        | Panasonic    | AG2400    | NTSC                      |
| Cassette     |              |           |                           |
| Recorder     |              |           |                           |
+--------------+--------------+-----------+---------------------------+

**Table 2.4.b Airborne Geophysical Equipment**

Table 2.4.c lists the components of the ground-based reference station.

+------------+------------------+--------+----------------------------+
| **E        | **Manufacturer** | **M    | **Type**                   |
| quipment** |                  | odel** |                            |
+------------+------------------+--------+----------------------------+
| Ma         | Scintrex         | CS-2   | Cesium Vapour, 2 Hz        |
| gnetometer |                  |        | Sampling,                  |
|            |                  |        |                            |
|            |                  |        | 0.005 nT Sensitivity, 0.01 |
|            |                  |        | nT Resolution              |
+------------+------------------+--------+----------------------------+
| GPS        | Sercel           | NR-103 | 10 Channel                 |
| Receiver   |                  |        |                            |
+------------+------------------+--------+----------------------------+

**Table 2.4.c Ground Reference Station**

The ground magnetometer was mounted in a magnetically quiet area; its
clock was synchronized with the GPS time signal. The GPS data logger
records all of the raw range data stream. The *Trajecto* differential
correction software matches the output from the airborne GPS system and
the ground GPS system during the data reduction process.

Table 2.4.d lists the equipment and software used to perform the field
processing.

  ------------------ ------------------ ----------------- -----------------
  **Equipment**      **Manufacturer**   **Model**         **Type**

  PC                 Dell               Inspiron 7500     800 MHz Pentium

  Printer            HP                 HP950C            A4 Colour

  Data Processing    Fugro Airborne     Gmaps             DOS & Windows
  Software           Surveys                              

  Image Processing   ERMapper           Version 5.5       Windows 95/98
  Software                                                

  GPS Processing     Sercel             Trajecto          DOS
  Software                                                
  ------------------ ------------------ ----------------- -----------------

**Table 2.4.d Field Processing System**

**3. PERSONNEL**

  --------------------- ---------------------- --------------------------
  **NAME**              **TITLE**              **PROJECT POSITION**

  Robb, Jeff            Aircraft Maintenance   Aircraft Maintenance
                        Engineer               

  Lamirande, Ken        Electronics Technician Electronics Operator

  Reed, Travis          Electronics Technician Electronics Operator

  Lyall, Ron            Operations Manager     Processor, Logistics

  Williston, Mark       Pilot                  Survey Pilot

  Thomas, Jeff          Pilot                  Survey Pilot
  --------------------- ---------------------- --------------------------

### Table 3 Field Project Personnel 

**4. SURVEY OPERATIONS**

1.  GENERAL

The production phase of the project began in Bishop, California, on
December 5^th^ , 2000, and the final production flight was made on
January 14^th^, 2001. The Comfort Inn provided crew accommodation and
space for the field processing office.

2.  DIURNAL CONDITIONS

Magnetic diurnal variation was exceptionally quiet. Deviations never
reached the specification limit.

3.  GENERAL WEATHER CONDITIONS

Weather conditions were frequently unfavourable for survey flying due to
high turbulence or cloud cover in the mountains. Ten days were lost.

4.  QUALITY CONTROL AND FIELD PROCESSING

-   To check the data for adherence to contract specifications and move
    the data closer to the final stage, the following procedures were
    followed for each flight (details in section 6):

-   downloading and verification of aircraft data;

-   downloading and verification of GPS and magnetic base station data;

-   post-processing of GPS data using SERCEL TRAJECTOGRAPHY software;

-   merging of navigation data with geophysical data including
    transformation of coordinates from WGS84 latitude/longitude to UTM
    x, y coordinates in the local spheroid;

-   creation of flight path plots and evaluation of compliance with
    contract specifications;

-   spike and null value location and removal from the magnetic and
    altimeter data;

-   computing of a drape surface quality control field for evaluation of
    compliance with the contract specifications;

-   computing of magnetic noise channel for evaluation of data quality
    and compliance with contract specifications;

-   evaluation of diurnal data quality, and compliance with contract
    specifications;

-   correction of magnetic data for I.G.R.F. gradient;

-   noise filtering of magnetic and altimeter fields;

-   correction of magnetic field for altitude deviations;

-   backing-up of all field data.

At regular intervals, the corrected magnetic data were levelled and
gridded for quality inspection including real-time shade enhancement.

**5. CALIBRATION AND TEST RESULTS**

5.1 GPS BASE STATION

To apply post-flight differential GPS corrections to the survey data, a
GPS base station was installed near the crew's hotel. The location of
the GPS base station antenna was determined by averaging positions over
a 24 hour period. The location was 37^o^ 22' 17.28" N latitude, 118^o^
22' 8.46" W longitude, elevation 1,255 m, on the WGS spheroid.

2.  MAGNETIC LAG TEST

The camera on-board the aircraft records its position, A, relative to
the ground, at time t0. In fact the sensor will arrive over A at time t1
(\>t0). Furthermore, because of electronic delays, the reading at time
t1 will not be recorded until time t2 (\>t1). The difference t2-t0
represents the lag between the actual aircraft position and the x y
position tied to the magnetic reading on disk. A lag test was performed
by flying the aircraft at survey altitude in opposite directions over a
sharp magnetic feature. The position of the magnetic feature was
referenced to a visible feature recorded by the video system, in this
case a bridge, which was the anomaly source. By superimposing a plot of
the east-west anomaly over the west-east anomaly, the video-picked
position of the bridge can be transposed onto its counterpart; and
one-half the difference between the two video-picked positions equals
the magnetic system lag. The lag was 0.7 seconds, or 7 magnetic samples,
for aircraft C-FZLK. These values were used to correct for magnetic
system lag throughout the survey.

![](media/image2.wmf)

![](media/image3.wmf)

5.3 GPS LAG / ACCURACY.TEST

A cloverleaf flown over the established co-ordinates of the Canadian
Geological Survey test site was used to measure the lag in the GPS
positioning, with regard to the video camera position. A value of 0.2
seconds resulted in a best fit with the video position. Once the lag is
applied (as in figure 5.3) the cloverleaf intersection is used to test
the accuracy of the GPS positioning.

  --------------- ---------- ---------- -------------------- ------------------ -- ------
  Aircraft:                             Cessna Caravan                             

  Registration:                         C-FZLK                                     

  Date:                                 November 25, 2000                          

  Location:                             Bourget, Ontario,                          
                                        Canada                                     

  Altitude:                             400 ft mean terrain                        
                                        clearance                                  

  DIRECTION       FIDUCIAL              OFFSET FROM TARGET   Line \# on Video      
                  CLOSEST TO            DUE TO PILOT ERROR                         
                  TARGET                                                           

                  (from                 (estimate in metres                        
                  video)                & direction)                               

  South           66216.56              0                    Line 10               

  West            66326.92              3 N                  Line 11               

  North           66413.50              20 E                 Line 12               

  East            66506.22              5 N                  Line 13               

  South           66595.44              5 W                  Line 14               

  West            66709.76              5 N                  Line 15               

  East            66884.10              0                    Line 17               

  North           66992.44              15 E                 Line 18               
  --------------- ---------- ---------- -------------------- ------------------ -- ------

TABLE 5.3 GPS LAG / ACCURACY TEST

![](media/image4.wmf)

5.4 FIGURE OF MERIT (FOM)

The figure of merit is the measurement of the ability of the
compensation system to remove the effects of aircraft maneuvers from the
total field data. During the FOM test the aircraft is flown into a quiet
magnetic area and put through a series of pitches (±5^o^), rolls
(±10^o^) and yaws (±5^o^) to examine the noise remaining in the signal
after the 27 term automatic compensation algorithm has been applied to
the data.

  --------------- --------------- --------------- --------------- ---------
                  **Figure of                                     
                  Merit**                                         

                                                                  

  Aircraft:                       Cessna Caravan                  

  Registration:                   C-FZLK                          

  Magnetometer:                   Cesium vapor,                   
                                  stinger mounted                 

  Sampling Rate:                  10 Hz                           

  Date:                           December 2,                     
                                  2000                            

  Location:                       Bishop,                         
                                  California                      

                                                                  

  HEADING         MANOEUVER       VALUE (nT)      HEADING         

                                                  TOTAL (nT)      

  NORTH           PITCH           0.18                            

                  ROLL            0.08                            

                  YAW             0.06            0.32            

                                                                  

  EAST            PITCH           0.12                            

                  ROLL            0.07                            

                  YAW             0.08            0.27            

                                                                  

  SOUTH           PITCH           0.08                            

                  ROLL            0.06                            

                  YAW             0.04            0.18            

                                                                  

  WEST            PITCH           0.08                            

                  ROLL            0.06                            

                  YAW             0.06            0.20            

                                  **FOM VALUE**   0.97            nT

  **AVERAGE                                                       
  MANEUVER NOISE                                                  
  ( FOM / 12 )**                                                  
  --------------- --------------- --------------- --------------- ---------

**Table 5.4 C-FZLK Figure of Merit**

5.5 ALTIMETER CALIBRATION

On November 24, 2000, the radar, barometric, and GPS altimeters were
compared by flying at terrain clearances of 200', 300', 400', 500',
600', 800', and 1000' over a flat portion of the Ottawa river. The
results reconfirmed that all altimeters aboard C-FZLK are functioning
normally.

**6. FINAL DATA PROCESSING**

Final data reduction was undertaken at the Fugro Airborne Surveys
processing center in Ottawa, Canada between January and February, 2001.
In general, final processing consisted of the following operations:

-   final levelling of the total field magnetic data;

-   image and 1:100,000 scale map analysis of the total field and
    levelling compensations by a geophysicist for any residual levelling
    or positioning errors or gridding artifacts;

-   correction of errors;

-   final gridding and micro-levelling;

-   imaging and plotting of magnetic field;

-   gridding of radar altimeter data

-   archiving of final data.

The final projection is Universal Transverse Mercator, using the NAD27
(Clarke 1866) spheroid. The datum shift from WGS 84 to Clarke 1866
(NAD27) was x = 8 m, y = -160 m, z = -176 m. The false easting is
500,000 m, false northing is 0 m, scale factor is 0.9996 and the central
meridian is 117^o^ West.

Further details of the magnetic processing are provided below.

6.1 Noise Editing

An automatic editing routine, employing 4^th^ differences of the
magnetic field, removed nulls and spikes down to the noise level, and
located abrupt level shifts.

6.2 Noise Filtering

We filtered all data in the frequency domain with a cutoff 0.061
(wavelengths per sample interval) rolloff 0.030 (wavelengths per sample
interval). This filter approaches 100% removal of anomalies of
wavelength 99 metres (13.2 samples x average speed of 7.5 metres/sample)
or less. It approaches 0% removal of anomalies of wavelength 163 metres
(21.7 samples x average speed of 7.5 metres/sample) or more. This filter
should have no effect on any real, geological-source anomalies; or even
the narrowest anomaly from cultural sources on the ground surface. The
minimum ground clearance is about 150 metres (rarely encountered) and
the minimum wavelength produced at 150 metres is roughly 2 x 150 = 300
metres. Thus all real wavelengths are a safe distance from the effective
limit of the filter (163 metres).

In the relatively quiet magnetic field recorded at high ground clearance
over the valleys (flight lines 101 to 167) a slightly longer wavelength
noise was found -- beyond the limit of the aforementioned filter. There
were several days of high wind turbulence; and noise from sudden
aircraft maneuvers can reach 4 second periods. Thus, a wider filter was
applied to these lines: cutoff 0.0193, rolloff 0.0100. This frequency
domain filter achieves near 100% removal of periods up to 4.1 seconds;
and its effect is near 0% at wavelengths of 524 metres or more. The
ground clearance was sufficient to ensure that all real wavelengths
would significantly exceed 524 metres; and this was verified by
extensive examination of profile data before and after filtering. To
reduce the likelihood of this filter change being visible in any
derivative image, a block of adjacent, high-ground-clearance lines (169
to 339) was smoothed with a third frequency domain filter (cutoff
0.0313, rolloff 0.0160), intermediate between the other two. As before,
the ground clearance was sufficient to ensure that all real wavelengths
would significantly exceed the effective limit of the filter (322
metres); and this was verified by extensive examination of profile data
before and after filtering.

6.3 Diurnal Subtraction

A test was made to verify the effectiveness of diurnal subtraction: Long
period diurnal variations were subtracted from the air data, as they are
more likely to correlate, and the residual magnetic field was leveled.
As no improvement was noted in the required levelling compensations,
diurnal subtraction was not employed.

6.4 IGRF Correction

The IGRF regional value was calculated using the 1995 model updated to
the mid-survey date (2000.9) using the corrected GPS elevations. Using
the actual elevations for IGRF correction has the added benefit of
correcting for the magnetic effect of altitude variations within the
Earth's primary field. Corrections for vertical movements within the
secondary magnetic field induced by the Earth's crust is discussed in
the following section, 6.5.

5.  Upward/Downward Continuation

As the terrain clearance drops, the vertical magnetic gradients can
become very high; and even minor deviations from the prescribed drape
surface may produce significant changes in the measured magnetic field.
The Taylor Expansion[^1] applies the required upward and downward
continuations to the magnetic field to simulate measurements from the
prescribed altitude. The resulting magnetic field profiles were input to
the levelling process.

6.  Levelling

The lines (traverse lines) and tie-lines (control lines) of an
aeromagnetic survey form a network, and the points where they cross are
called intersections. At each intersection the magnetic values should be
identical. In practice they differ as a result of:

> \- time variations of the magnetic field;
>
> \- heading effects;
>
> \- altitude differences;
>
> \- position errors;
>
> \- cultural or instrument noise.

In the levelling process, it is assumed that most of the required level
adjustments will vary smoothly along each line or tie-line. The network
of line minus tie-line differences at the intersections is analyzed to
produce a matrix of misclosures. These misclosures were reduced to zero
through an iterative process of tilting the profile baselines and moving
the intersection locations. Compensation values applied at adjacent
tie-lines were not allowed to differ by more than 5 nT. Intersection
movements were restricted to a maximum of 4 samples (about 30 metres).
These maximums were very rarely required. Of the 6,717 intersections,
less than 87 could not be closed with these compensations. These
intersections were carefully checked and corrected manually.

6.7 Gridding

Gridding was done by the Akima method, using data from all lines and
tie-lines. A gridding interval of 1/3 the line spacing was used (133 m).

6.8 Grid Levelling

The final stage of levelling consisted of applying a grid-levelling
routine to the gridded data to remove small residual errors that are not
properly removed by conventional levelling of the line data[^2]

**7. DELIVERABLES**

7.1 MAPS

Two copies of the magnetic field contour map are presented at 1:100,000
scale with UTM registration plus screened flight path, in black and
white, on mylar.

7.2 REPORT

This report covers data acquisition and processing, and is provided in
two hard copies plus a digital archive in *Microsoft Word* format.

7.3 DIGITAL ARCHIVES

Files: raw and final processed profile data, and final magnetic and
radar altitude grids;

Format: The ASCII format is used for profiles, and *Geosoft* binary
format is used for grids. A full format description is included in the
appendix .

Media: CD-ROM.

Copies: two

We trust this survey will assist your mapping program; and we remain
available for questions at any time.

Respectfully Submitted,

Brian Schacht P. Geoph.

**APPENDIX**

**DIGITAL ARCHIVE FORMAT DESCRIPTOR**

DIGITAL ARCHIVE DESCRIPTION OF PROFILE DATA

Digital Archive is Ascii.

Ascii filename: **nevada.archive**

250 bytes I 10 format

1-10 Line number X 100 + part number

11-20 Flight number

21-30 Latitude **NAD27** (decimal degrees)

31-40 Longitude

41-50 UTM metres **NAD27** (CM 117 degrees west)

51-60 UTM metres

61-70 Latitude **WGS84** (decimal degrees)

71-80 Longitude

81-90 UTM metres **WGS84** (CM 117 degrees west)

91-100 UTM metres

101-110 Fiducial (seconds UTC X 10 increments by 1)

111-120 Date (ddmmyy)

121-130 Radar (m X 100)

131-140 Baro (m X 100)

141-150 GPS elevation (m X 100)

151-160 Diurnal (.001 nT)

161-170 Raw Magnetics (.001 nT) edited, lag applied.

171-180 Filtered Magnetics (.001 nT)

181-190 Filtered Magnetics - I.G.R.F. (.001 nT)

191-200 I.G.R.F. (2000.9)

201-210 Differential Up/Down corr. Magnetics (.001 nT)

211-220 Levelled Magnetics (.001 nT)

221-230 Final Magnetics (.001 nT)

231-240 Compensation (.001 nT) from TL levelling

241-250 Compensation (.001 nT) from micro levelling

Fugro Airborne Survey\'s direction codes are as follows:

1: Northbound

2: Eastbound

3: Southbound

4: Westbound

The archive file contains the following lines:

ARCHIVE FILE: **nevada.archive**

LINE-ID DIR FST-FID LST-FID TAPE BLOCK REC SAMPLES

\-\-\-\-\-\-\-\-\-\-- \-\-- (X10) (X10) \-\-\-- \-\-\-\-- \-\--
\-\-\-\-\-\--

10101 3 70026 70106 1 1 1 801

10301 1 70252 70339 1 802 1 871

10501 3 70515 70606 1 1673 1 911

10701 1 70726 70822 1 2584 1 961

10901 3 70945 71048 1 3545 1 1031

11101 1 71179 71286 1 4576 1 1071

11301 3 71438 71565 1 5647 1 1271

11502 1 76602 76709 1 6918 1 1071

11701 3 59673 59773 1 7989 1 1001

11901 1 59906 60011 1 8990 1 1051

12101 3 60146 60248 1 10041 1 1021

12301 1 60376 60490 1 11062 1 1141

12501 3 60627 60739 1 12203 1 1121

12701 1 60871 60994 1 13324 1 1231

12901 3 61131 61250 1 14555 1 1191

13101 1 61378 61510 1 15746 1 1321

13301 3 61655 61781 1 17067 1 1261

13502 3 76791 76927 1 18328 1 1361

13701 3 62202 62336 1 19689 1 1341

13901 1 62456 62604 1 21030 1 1481

14101 3 62759 62899 1 22511 1 1401

14301 1 63029 63178 1 23912 1 1491

14501 3 63330 63485 1 25403 1 1551

14702 1 77077 77252 1 26954 1 1751

14901 3 63937 64095 1 28705 1 1581

15101 1 64227 64401 1 30286 1 1741

15301 3 64739 64905 1 32027 1 1661

15501 1 65036 65213 1 33688 1 1771

15701 3 65363 65537 1 35459 1 1741

15901 1 65666 65853 1 37200 1 1871

16102 3 77382 77558 1 39071 1 1761

16301 1 66297 66486 1 40832 1 1891

16501 3 66643 66830 1 42723 1 1871

16701 1 66955 67157 1 44594 1 2021

16901 3 67308 67501 1 46615 1 1931

17101 1 67623 67829 1 48546 1 2061

17301 3 67986 68175 1 50607 1 1891

17501 1 68318 68522 1 52498 1 2041

17701 3 68949 69154 1 54539 1 2051

17901 1 69305 69509 1 56590 1 2041

18101 1 77097 77309 1 58631 1 2121

18301 3 77483 77679 1 60752 1 1961

18501 1 77823 78025 1 62713 1 2021

18701 3 78180 78377 1 64734 1 1971

18901 1 78528 78736 1 66705 1 2081

19101 3 78891 79091 1 68786 1 2001

19301 1 79269 79483 1 70787 1 2141

19501 1 78113 78319 1 72928 1 2061

19701 3 78459 78658 1 74989 1 1991

19901 1 78807 79007 1 76980 1 2001

20101 3 56671 56896 1 78981 1 2251

20301 1 57068 57301 1 81232 1 2331

20501 3 57466 57694 1 83563 1 2281

20701 1 57880 58118 1 85844 1 2381

20901 3 58563 58793 1 88225 1 2301

21101 1 58968 59206 1 90526 1 2381

21301 3 59361 59602 1 92907 1 2411

21501 1 59762 59991 1 95318 1 2291

21701 3 60210 60434 1 97609 1 2241

21901 1 60589 60815 1 99850 1 2261

22101 3 60995 61209 1 102111 1 2141

22301 1 61369 61598 1 104252 1 2291

22501 3 61771 61995 1 106543 1 2241

22701 1 62142 62371 1 108784 1 2291

22901 3 62810 63049 1 111075 1 2391

23101 1 63210 63445 1 113466 1 2351

23301 3 63636 63879 1 115817 1 2431

23501 1 64037 64253 1 118248 1 2161

23701 3 64426 64656 1 120409 1 2301

23901 1 64808 65022 1 122710 1 2141

24101 3 65206 65430 1 124851 1 2241

24301 1 65593 65800 1 127092 1 2071

24501 3 65983 66197 1 129163 1 2141

24701 1 66340 66541 1 131304 1 2011

24901 3 66820 67034 1 133315 1 2141

25101 1 67174 67360 1 135456 1 1861

25301 3 67545 67736 1 137317 1 1911

25501 1 67876 68057 1 139228 1 1811

25701 1 74360 74519 1 141039 1 1591

25901 3 74676 74844 1 142630 1 1681

26101 1 74989 75136 1 144311 1 1471

26301 3 75286 75448 1 145782 1 1621

26501 1 75580 75721 1 147403 1 1411

26701 3 75875 76032 1 148814 1 1571

26902 1 77826 77967 1 150385 1 1411

27101 3 76464 76621 1 151796 1 1571

27301 1 76750 76876 1 153367 1 1261

27501 3 77035 77178 1 154628 1 1431

27701 1 77304 77423 1 156059 1 1191

27901 3 77568 77708 1 157250 1 1401

28101 1 77838 77948 1 158651 1 1101

28301 3 78092 78224 1 159752 1 1321

28501 1 78354 78458 1 161073 1 1041

28701 3 78627 78745 1 162114 1 1181

28901 1 78875 78974 1 163295 1 991

29101 3 79114 79230 1 164286 1 1161

29301 1 79355 79446 1 165447 1 911

29501 3 79588 79695 1 166358 1 1071

29701 1 79828 79916 1 167429 1 881

29901 3 80056 80166 1 168310 1 1101

30101 1 80289 80369 1 169411 1 801

30301 3 80515 80613 1 170212 1 981

30501 1 80736 80811 1 171193 1 751

30701 3 80953 81055 1 171944 1 1021

30901 1 81182 81261 1 172965 1 791

31101 3 81398 81494 1 173756 1 961

31301 1 81622 81701 1 174717 1 791

31501 3 81843 81939 1 175508 1 961

31701 1 82067 82142 1 176469 1 751

31901 3 82273 82370 1 177220 1 971

32101 1 82488 82563 1 178191 1 751

32301 3 82699 82798 1 178942 1 991

32501 1 82918 82991 1 179933 1 731

32701 3 83135 83232 1 180664 1 971

32901 1 83364 83441 1 181635 1 771

33101 3 83583 83680 1 182406 1 971

33301 1 83810 83886 1 183377 1 761

33501 3 74089 74192 1 184138 1 1031

33701 3 76673 76774 1 185169 1 1011

33901 3 58884 58980 1 186180 1 961

34101 1 57161 57677 1 187141 1 5161

34301 3 69985 70506 1 192302 1 5211

34501 1 76005 76513 1 197513 1 5081

34701 3 80461 81036 1 202594 1 5751

34901 3 79681 80180 1 208345 1 4991

35101 1 58460 59065 1 213336 1 6051

35302 1 55198 55802 1 219387 1 6041

35501 3 68335 68939 1 225428 1 6041

35701 1 73472 73968 1 231469 1 4961

35901 3 84018 84555 1 236430 1 5371

36101 1 81171 81684 1 241801 1 5131

36301 3 81886 82457 1 246932 1 5711

36501 1 82608 83136 1 252643 1 5281

36701 3 83353 83938 1 257924 1 5851

36901 1 84190 84622 1 263775 1 4321

36902 1 75887 76000 1 268096 1 1131

37101 3 84820 85421 1 269227 1 6011

37301 1 85675 86230 1 275238 1 5551

37501 3 86433 87050 1 280789 1 6171

37701 1 84660 85143 1 286960 1 4831

37901 3 85293 85844 1 291791 1 5511

38101 1 57165 57722 1 297302 1 5571

38301 3 58326 58982 1 302873 1 6561

38501 1 59179 59738 1 309434 1 5591

38701 3 60079 60699 1 315025 1 6201

38901 1 60885 61458 1 321226 1 5731

39101 3 61619 62216 1 326957 1 5971

39301 1 62379 62978 1 332928 1 5991

39501 3 63147 63751 1 338919 1 6041

39701 1 63920 64506 1 344960 1 5861

39901 3 64864 65484 1 350821 1 6201

40101 1 65667 66254 1 357022 1 5871

40301 3 66477 67099 1 362893 1 6221

40501 1 67263 67844 1 369114 1 5811

40701 3 67992 68615 1 374925 1 6231

40901 1 68794 69365 1 381156 1 5711

41101 3 68735 69297 1 386867 1 5621

41301 1 67960 68587 1 392488 1 6271

41501 3 67214 67792 1 398759 1 5781

41701 1 66440 67039 1 404540 1 5991

41901 3 65693 66257 1 410531 1 5641

42101 1 63690 64294 1 416172 1 6041

42301 3 62946 63515 1 422213 1 5691

42501 1 62159 62784 1 427904 1 6251

42701 3 61393 62002 1 434155 1 6091

42901 1 60582 61209 1 440246 1 6271

43101 3 59844 60404 1 446517 1 5601

43301 1 58825 59427 1 452118 1 6021

43501 3 58106 58663 1 458139 1 5571

43701 1 57214 57817 1 463710 1 6031

43901 3 86452 86986 1 469741 1 5341

44101 1 85795 86310 1 475082 1 5151

44301 3 85148 85672 1 480233 1 5241

44501 1 84493 85006 1 485474 1 5131

44701 3 83607 83740 1 490605 1 1331

44702 3 83945 84374 1 491936 1 4291

44901 1 82954 83477 1 496227 1 5231

45101 3 82281 82830 1 501458 1 5491

45301 1 81623 82141 1 506949 1 5181

45501 3 80938 81489 1 512130 1 5511

45701 1 80282 80793 1 517641 1 5111

45901 3 79611 80151 1 522752 1 5401

46101 1 78961 79472 1 528153 1 5111

46301 3 78169 78707 1 533264 1 5381

46501 1 77309 77825 1 538645 1 5161

46701 3 76639 77188 1 543806 1 5491

46901 1 75993 76510 1 549297 1 5171

47101 3 75309 75864 1 554468 1 5551

47301 1 74674 75180 1 560019 1 5061

47501 3 68251 68918 1 565080 1 6671

47701 1 67511 68067 1 571751 1 5561

47901 3 66753 67350 1 577312 1 5971

48101 1 65852 66416 1 583283 1 5641

48301 3 65084 65713 1 588924 1 6291

48501 1 64339 64921 1 595215 1 5821

48701 3 63565 64194 1 601036 1 6291

48902 3 56419 56988 1 607327 1 5691

49101 3 62089 62702 1 613018 1 6131

49301 1 61160 61745 1 619149 1 5851

49501 3 60379 61007 1 625000 1 6281

49701 1 59622 60208 1 631281 1 5861

49901 3 58880 59477 1 637142 1 5971

50101 1 58113 58711 1 643113 1 5981

50301 3 57360 57973 1 649094 1 6131

50502 1 55650 56306 1 655225 1 6561

50701 3 86365 86886 1 661786 1 5211

50901 1 85708 86234 1 666997 1 5261

51101 3 84741 85278 1 672258 1 5371

51301 1 84094 84613 1 677629 1 5191

51501 3 83440 83969 1 682820 1 5291

51701 1 82784 83311 1 688111 1 5271

51901 3 82117 82657 1 693382 1 5401

52101 1 81471 81991 1 698783 1 5201

52301 3 80808 81348 1 703984 1 5401

52501 1 80147 80662 1 709385 1 5151

52701 3 79495 80021 1 714536 1 5261

52901 1 79110 79360 1 719797 1 2501

52903 3 79360 79658 1 722298 1 2981

53101 3 78167 78702 1 725279 1 5351

53301 1 77507 78030 1 730630 1 5231

53501 3 76839 77368 1 735861 1 5291

53701 1 76450 76713 1 741152 1 2631

53702 3 70320 70631 1 743783 1 3111

53901 3 75528 75790 1 746894 1 2621

53902 3 80280 80582 1 749515 1 3021

54101 1 74865 75386 1 752536 1 5211

54301 3 74199 74729 1 757747 1 5301

54501 1 73531 74044 1 763048 1 5131

54701 3 68288 68893 1 768179 1 6051

54901 1 67508 68083 1 774230 1 5751

55101 3 66736 67363 1 779981 1 6271

55301 1 65843 66408 1 786252 1 5651

55501 3 65035 65704 1 791903 1 6691

55701 1 64273 64842 1 798594 1 5691

55901 3 63493 64111 1 804285 1 6181

56101 1 62492 63079 1 810466 1 5871

56301 3 61683 62335 1 816337 1 6521

56501 1 60931 61507 1 822858 1 5761

56701 3 60128 60789 1 828619 1 6611

56901 1 59406 59955 1 835230 1 5491

57101 3 58361 59002 1 840721 1 6411

57301 1 57630 58180 1 847132 1 5501

57501 3 56850 57477 1 852633 1 6271

57701 1 56116 56670 1 858904 1 5541

57901 3 86163 86646 1 864445 1 4831

58101 1 85492 86034 1 869276 1 5421

58301 3 84865 85350 1 874697 1 4851

58501 1 84201 84745 1 879548 1 5441

58701 3 83572 84064 1 884989 1 4921

58901 1 82879 83429 1 889910 1 5501

59101 3 82018 82520 1 895411 1 5021

59301 1 81344 81891 1 900432 1 5471

59501 3 80713 81201 1 905903 1 4881

59701 1 80028 80576 1 910784 1 5481

59901 3 79396 79883 1 916265 1 4871

60101 1 78714 79266 1 921136 1 5521

60301 3 78022 78514 1 926657 1 4921

60501 1 77359 77899 1 931578 1 5401

60701 3 76704 77203 1 936979 1 4991

60901 1 76030 76320 1 941970 1 2901

60902 3 69813 70100 1 944871 1 2871

61101 3 75347 75857 1 947742 1 5101

61301 1 74647 75194 1 952843 1 5471

61501 3 69643 70238 1 958314 1 5951

61701 1 68880 69489 1 964265 1 6091

61901 3 67874 68482 1 970356 1 6081

62101 1 66893 67501 1 976437 1 6081

62301 3 66137 66729 1 982518 1 5921

62501 1 65146 65746 1 988439 1 6001

62701 3 64384 64985 1 994440 1 6011

62901 1 63499 64093 1 1000451 1 5941

63101 3 76094 76696 1 1006392 1 6021

63301 1 75068 75679 1 1012413 1 6111

63501 3 74234 74909 1 1018524 1 6751

63701 1 73441 74059 1 1025275 1 6181

63901 3 72641 73269 1 1031456 1 6281

64101 3 85335 85972 1 1037737 1 6371

64301 1 84493 85170 1 1044108 1 6771

64501 3 83720 84316 1 1050879 1 5961

64701 1 82860 83515 1 1056840 1 6551

64901 3 81936 82520 1 1063391 1 5841

65101 1 81102 81769 1 1069232 1 6671

65301 3 80341 80924 1 1075903 1 5831

65501 1 79490 80134 1 1081734 1 6441

65701 1 77666 78315 1 1088175 1 6491

65901 3 58249 58880 1 1094666 1 6311

66101 1 57440 58076 1 1100977 1 6361

66301 3 77010 77621 1 1107338 1 6111

66501 1 76125 76829 1 1113449 1 7041

66701 3 75133 75745 1 1120490 1 6121

66901 1 74301 74956 1 1126611 1 6551

67101 3 73186 73865 1 1133162 1 6791

67301 1 72350 73006 1 1139953 1 6561

67501 3 71117 71785 1 1146514 1 6681

67701 1 70291 70956 1 1153195 1 6651

67901 3 69471 70104 1 1159846 1 6331

68101 1 68651 69294 1 1166177 1 6431

68301 3 67639 68294 1 1172608 1 6551

68501 1 66862 67483 1 1179159 1 6211

68701 3 66067 66690 1 1185370 1 6231

68901 1 65324 65908 1 1191601 1 5841

69101 3 64254 64874 1 1197442 1 6201

69301 1 63538 64111 1 1203643 1 5731

69501 3 62730 63346 1 1209374 1 6161

69701 1 62000 62576 1 1215535 1 5761

69901 3 85972 86556 1 1221296 1 5841

70101 1 85324 85844 1 1227137 1 5201

70301 3 84589 85159 1 1232338 1 5701

70501 1 83911 84423 1 1238039 1 5121

70701 3 83175 83742 1 1243160 1 5671

70901 1 82505 83019 1 1248831 1 5141

71101 3 81511 82032 1 1253972 1 5211

71301 1 80936 81396 1 1259183 1 4601

71501 3 80256 80765 1 1263784 1 5091

71701 1 79697 80138 1 1268875 1 4411

71901 3 79033 79515 1 1273286 1 4821

72101 1 78453 78869 1 1278107 1 4161

72301 3 77568 78017 1 1282268 1 4491

72501 1 77022 77412 1 1286759 1 3901

72701 3 76406 76823 1 1290660 1 4171

72901 1 75831 76212 1 1294831 1 3811

73101 3 75239 75645 1 1298642 1 4061

73301 1 74632 75002 1 1302703 1 3701

73502 3 66293 66693 1 1306404 1 4001

73702 1 65675 66067 1 1310405 1 3921

73902 3 65035 65478 1 1314326 1 4431

74102 1 64386 64785 1 1318757 1 3991

74303 3 63620 64052 1 1322748 1 4321

74503 1 63023 63415 1 1327069 1 3921

500102 2 61915 62736 1 1330990 1 8211

500301 4 65300 66006 1 1339201 1 7061

500501 2 67035 67700 1 1346262 1 6651

500701 4 62953 63618 1 1352913 1 6651

500901 2 63740 64370 1 1359564 1 6301

501101 4 59654 60375 1 1365865 1 7211

501301 4 64520 65169 1 1373076 1 6491

501501 2 65290 65925 1 1379567 1 6351

501701 2 60576 61271 1 1385918 1 6951

501901 4 66012 66674 1 1392869 1 6621

502101 2 66793 67420 1 1399490 1 6271

502301 4 61575 62300 1 1405761 1 7251

502501 4 67500 68154 1 1413012 1 6541

502701 2 68268 68911 1 1419553 1 6431

502901 2 62573 63280 1 1425984 1 7071

503101 4 69013 69648 1 1433055 1 6351

503301 2 69775 70402 1 1439406 1 6271

503501 4 63456 64152 1 1445677 1 6961

503701 4 70537 71127 1 1452638 1 5901

503901 2 71255 71811 1 1458539 1 5561

504101 2 64310 64978 1 1464100 1 6681

504301 4 71915 72471 1 1470781 1 5561

504501 2 72595 73154 1 1476342 1 5591

504701 4 65177 65868 1 1481933 1 6911

504901 4 73253 74056 1 1488844 1 8031

505101 2 74167 74957 1 1496875 1 7901

505301 2 66375 67301 1 1504776 1 9261

505501 4 75056 75908 1 1514037 1 8521

505701 4 76466 76731 1 1522558 1 2651

505901 2 68908 69214 1 1525209 1 3061

506101 2 76836 77083 1 1528270 1 2471

506301 4 77253 77473 1 1530741 1 2201

506501 4 69426 69666 1 1532942 1 2401

506701 4 67706 68696 1 1535343 1 9901

506901 2 76053 76324 1 1545244 1 2711

507101 3 77751 77955 1 1547955 1 2041

507301 1 81025 81272 1 1549996 1 2471

507501 3 79185 79340 1 1552467 1 1551

DIGITAL ARCHIVE DESCRIPTION OF GRID DATA

CLIENT U.S.G.S

NAME OF SURVEY AEROMAGNETIC SURVEY of **WESTERN NEVADA**

AREA NAME **EXCELSIOR MOUNTAINS, SOUTHERN WASSUK RANGE and EXCELSIOR
ADD-ON**

CONTRACTOR FUGRO AIRBORNE SURVEYS

JOB CODE 655

GRID ARCHIVE NAME NEVADA_TF.GRD

FORMAT GEOSOFT BINARY GRID

CONTENT **TOTAL MAGNETIC INTENSITY**

CREATION DATE February 15, 2001

NUMBER of ROWS and COLUMNS 640 1024

PIVOTAL POSITION (X,Y) 331087 4212084

CELL SIZE 83m

UNIT nT

UNIT FACTOR 0.001

MINIMUM VALUE (nT) -555.284

MAXIMUM VALUE (nT) 846.571

MEAN VALUE (nT) -71.181

GRID ARCHIVE NAME NEVADA_RADAR.GRD

FORMAT GEOSOFT BINARY GRID

CONTENT **RADAR**

CREATION DATE March 7, 2001

NUMBER of ROWS and COLUMNS 640 1024

PIVOTAL POSITION (X,Y) 331087 4212167

CELL SIZE 83m

UNIT m

UNIT FACTOR 0.01

MINIMUM VALUE (m) 157

MAXIMUM VALUE (m) 1217 (instrument maximum)

MEAN VALUE (m) 536

PROJECTION INFORMATION :

DATUM NAD27

SHEROID CLARKE 1866

PROJECTION UTM

CENTRAL MERIDIEN 117 West

FALSE EASTING 500000 m

FALSE NORTHING 0 m

SCALE FACTOR 0.9996

[^1]: Pilkington, M., and Thurston, J. B., 2001. *Draping corrections
    for aeromagnetic data: line versus grid based approaches*;
    Exploration Geophysics, in press.

[^2]: Minty, B.R.S., 1991*: Simple micro-levelling for aeromagnetic
    data*; Exploration Geophysics, v.22, p. 591-592.