**FINAL REPORT**

on

**Data Acquisition and Processing**

for the

**Airborne Magnetic Survey**

of

**Death Valley, California**

on behalf of the

**United States Geological Survey**

Brian Schacht P. Geoph.

Ottawa, Ontario, Canada

March, 2001

**TABLE OF CONTENTS**

**1. INTRODUCTION 3**

**2. TECHNICAL SPECIFICATIONS 4**

1.  SURVEY LOCATION 4

2.  FLIGHT SPECIFICATIONS 4

2.3 TOLERANCES 4

2.4 SURVEY EQUIPMENT 5

**3. PERSONNEL 6**

**4. SURVEY OPERATIONS 7**

4.1 GENERAL 7

4.2 DIURNAL CONDITIONS 7

4.3 GENERAL WEATHER CONDITIONS 7

4.4 QUALITY CONTROL AND FIELD PROCESSING 7

**5. CALIBRATION AND TEST RESULTS 8**

5.1 GPS BASE STATION 8

5.2 MAGNETIC LAG TEST 8

5.3 GPS LAG / ACCURACY TEST 9

5.4 FIGURE OF MERIT 11

5.  ALTIMETER CALIBRATION 11

**6. FINAL MAGNETIC DATA PROCESSING 12**

6.1 NOISE EDITING 12

6.2 NOISE FILTERING 12

6.3 DIURNAL SUBTRACTION 12

6.4 IGRF CORRECTION 12

6.5 UPWARD/DOWNWARD CONTINUATION 13

6.6 LEVELLING 13

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 Death Valley, California, as well
as three conjoined areas within western Nevada. 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.png){width="6.057638888888889in"
height="7.485416666666667in"}

######## 

**2. TECHNICAL SPECIFICATIONS** 4

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 area is bounded by the following co-ordinates (WGS84 UTM and degrees
X 1,000,000):

500000.00 3979126.00 35572348 -117000000

552103.00 3979126.00 35571847 -116252002

512687.00 4039215.00 36295343 -116513001

512646.00 4066946.00 36445341 -116513002

470243.00 4066988.00 36445340 -117200003

470163.00 4043879.00 36322342 -117200002

500000.00 4043828.00 36322345 -117000000

2.2 FLIGHT SPECIFICATIONS

Traverse Line Direction E - W

Traverse Line Spacing 400 m

Control Line Direction N - S

Control Line Spacing approximately 7,500 m

Terrain Clearance 117-1217 m+ - see section 2.3 - "Flying Height"

Line kilometers 8135.82 (5055.5 miles)

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 the survey necessitated a
    pre-planned drape surface with ground clearance exceeding 1217 m
    (4000') over the valley (the radar altimeter maximum is 1217 m).
    Less than 1% of the data could be flown below 183 m (600').

######### Magnetic Diurnal

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

    [Airborne Magnetometer Noise]{.underline}

```{=html}
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```
-   "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 levelling,
    positioning, or gridding errors;

-   final gridding and micro-levelling;

-   imaging and plotting of magnetic field;

-   gridding of radar altimeter data

-   archiving of final data.

The final projection was the Universal Transverse Mercator using the
NAD83 (WGS84) spheroid, with a false easting of 500,000 m, false
northing of 0 m, scale factor of 0.9996 and central meridian of 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 163 metre
limit of the filter.

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 (2001.0) 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. None of the 1,121
intersections needed manual corrections.

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

**DEATH VALLEY, CALIFORNIA**

Digital Archive is Ascii.

Ascii filename: **california.profile**

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: **california.archive**

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

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

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

10101 3 56599 56919 1 1 1 3201

10201 1 57317 57633 1 3202 1 3161

10301 3 57805 58137 1 6363 1 3321

10401 1 58333 58680 1 9684 1 3471

10501 3 58827 59175 1 13155 1 3481

10601 1 59378 59711 1 16636 1 3331

10701 3 59874 60216 1 19967 1 3421

10801 1 60372 60692 1 23388 1 3201

10901 3 60863 61204 1 26589 1 3411

11001 1 61368 61712 1 30000 1 3441

11101 3 62470 62805 1 33441 1 3351

11201 1 62997 63320 1 36792 1 3231

11301 3 63483 63825 1 40023 1 3421

11401 1 63981 64318 1 43444 1 3371

11501 3 64468 64806 1 46815 1 3381

11601 1 64970 65316 1 50196 1 3461

11701 3 65484 65815 1 53657 1 3311

11801 1 65965 66298 1 56968 1 3331

11901 3 66858 67223 1 60299 1 3651

12001 1 67385 67721 1 63950 1 3361

12101 3 68016 68355 1 67311 1 3391

12201 1 68523 68861 1 70702 1 3381

12301 3 69021 69365 1 74083 1 3441

12401 1 69526 69861 1 77524 1 3351

12501 3 70035 70369 1 80875 1 3341

12601 1 70565 70909 1 84216 1 3441

12701 3 71675 72011 1 87657 1 3361

12801 1 72199 72524 1 91018 1 3251

12901 3 72693 73040 1 94269 1 3471

13001 1 73211 73544 1 97740 1 3331

13101 3 56169 56532 1 101071 1 3631

13201 1 56725 57075 1 104702 1 3501

13301 3 57228 57588 1 108203 1 3601

13401 1 57777 58118 1 111804 1 3411

13501 3 58255 58611 1 115215 1 3561

13601 1 58801 59151 1 118776 1 3501

13701 3 59635 59979 1 122277 1 3441

13801 1 60138 60497 1 125718 1 3591

13901 3 60669 61010 1 129309 1 3411

14001 1 61179 61569 1 132720 1 3901

14101 3 61732 62077 1 136621 1 3451

14201 1 62245 62605 1 140072 1 3601

14301 3 62807 63140 1 143673 1 3331

14401 1 63306 63689 1 147004 1 3831

14501 3 63857 64203 1 150835 1 3461

14601 1 64359 64717 1 154296 1 3581

14701 3 65016 65361 1 157877 1 3451

14801 1 65532 65897 1 161328 1 3651

14901 3 66057 66398 1 164979 1 3411

15001 1 66571 66924 1 168390 1 3531

15101 3 67093 67445 1 171921 1 3521

15201 1 67618 67966 1 175442 1 3481

15301 3 68150 68498 1 178923 1 3481

15401 1 68680 69033 1 182404 1 3531

15501 1 70448 70802 1 185935 1 3541

15601 3 69954 70306 1 189476 1 3521

15701 1 69284 69641 1 192997 1 3571

15801 3 68659 69020 1 196568 1 3611

15901 3 67470 67845 1 200179 1 3751

16001 1 68003 68355 1 203930 1 3521

16101 1 66832 67178 1 207451 1 3461

16201 3 66257 66622 1 210912 1 3651

16301 1 65616 65982 1 214563 1 3661

16401 3 65087 65446 1 218224 1 3591

16501 1 64482 64838 1 221815 1 3561

16601 3 63886 64249 1 225376 1 3631

16701 1 63255 63621 1 229007 1 3661

16801 3 62699 63070 1 232668 1 3711

16901 1 86129 86437 1 236379 1 3081

17001 3 85574 85871 1 239460 1 2971

17101 1 85136 85452 1 242431 1 3161

17201 3 84704 85001 1 245592 1 2971

17301 1 67006 67373 1 248563 1 3671

17401 3 66479 66822 1 252234 1 3431

17501 3 83850 85044 1 255665 1 11941

17601 1 85554 86676 1 267606 1 11221

17701 3 57132 58313 1 278827 1 11811

17801 1 58501 59921 1 290638 1 14201

17901 3 60085 60930 1 304839 1 8451

17902 3 61160 61525 1 313290 1 3651

18001 1 61709 63120 1 316941 1 14111

18101 3 63550 64737 1 331052 1 11871

18201 1 64931 66355 1 342923 1 14241

18301 3 73525 74634 1 357164 1 11091

18402 1 75260 76170 1 368255 1 9101

18403 1 72995 73260 1 377356 1 2651

18501 3 76316 76990 1 380007 1 6741

18502 3 77280 77614 1 386748 1 3341

18503 1 73350 73500 1 390089 1 1501

18601 1 77781 78960 1 391590 1 11791

18701 3 79099 80190 1 403381 1 10911

18801 1 80345 81526 1 414292 1 11811

18901 3 81898 82997 1 426103 1 10991

19001 1 83388 84554 1 437094 1 11661

19101 3 56456 57802 1 448755 1 13461

19201 1 57955 59215 1 462216 1 12601

19301 3 59411 60810 1 474817 1 13991

19401 1 61151 62424 1 488808 1 12731

19502 3 57921 59149 1 501539 1 12281

19602 3 63306 64511 1 513820 1 12051

19701 3 58450 59641 1 525871 1 11911

19801 1 72673 74014 1 537782 1 13411

19901 3 57786 58990 1 551193 1 12041

20001 1 72810 74165 1 563234 1 13551

20101 1 71464 72790 1 576785 1 13261

20201 3 71588 72709 1 590046 1 11211

20301 3 63014 64235 1 601257 1 12211

20401 1 72637 73883 1 613468 1 12461

20501 1 72401 73679 1 625929 1 12781

20601 1 68737 70032 1 638710 1 12951

20702 1 59347 60283 1 651661 1 9361

20802 3 60465 61289 1 661022 1 8241

20902 1 61483 62401 1 669263 1 9181

21002 3 62706 63521 1 678444 1 8151

21102 1 63709 64590 1 686595 1 8811

21202 3 64741 65541 1 695406 1 8001

21302 1 65726 66602 1 703407 1 8761

21402 3 66868 67633 1 712168 1 7651

21502 1 67800 68634 1 719819 1 8341

21602 3 68855 69609 1 728160 1 7541

21702 1 64867 65837 1 735701 1 9701

21802 3 66112 66819 1 745402 1 7071

21901 1 67035 67947 1 752473 1 9121

22001 3 68098 68788 1 761594 1 6901

22101 1 59957 60785 1 768495 1 8281

22201 3 61284 61971 1 776776 1 6871

22301 1 62142 62900 1 783647 1 7581

22401 3 63070 63729 1 791228 1 6591

22501 1 63931 64736 1 797819 1 8051

22601 3 64902 65557 1 805870 1 6551

22701 1 65756 66504 1 812421 1 7481

22801 3 66724 67361 1 819902 1 6371

22901 1 67584 68305 1 826273 1 7211

23001 3 68466 69090 1 833484 1 6241

23101 1 69328 70002 1 839725 1 6741

23201 3 70176 70800 1 846466 1 6241

23301 1 70959 71600 1 852707 1 6411

23401 3 71799 72373 1 859118 1 5741

23501 1 59500 59991 1 864859 1 4911

23502 1 64816 64975 1 869770 1 1591

23601 3 60184 60739 1 871361 1 5551

23701 1 60894 61494 1 876912 1 6001

23801 3 61736 62291 1 882913 1 5551

23901 1 62467 63049 1 888464 1 5821

24001 3 63199 63737 1 894285 1 5381

24101 1 63900 64454 1 899666 1 5541

24201 3 64652 65177 1 905207 1 5251

24301 1 65350 65885 1 910458 1 5351

24401 3 66125 66625 1 915809 1 5001

24501 1 67102 67626 1 920810 1 5241

24601 3 67804 68297 1 926051 1 4931

24701 1 68481 68985 1 930982 1 5041

24801 3 69168 69653 1 936023 1 4851

24901 1 69811 70304 1 940874 1 4931

25001 3 70595 71066 1 945805 1 4711

25101 1 71288 71769 1 950516 1 4811

25201 3 71928 72392 1 955327 1 4641

25301 1 70020 70469 1 959968 1 4491

25401 3 70640 71087 1 964459 1 4471

25501 1 59595 60040 1 968930 1 4451

25601 3 60220 60650 1 973381 1 4301

25701 1 60824 61247 1 977682 1 4231

25801 3 61770 62192 1 981913 1 4221

25901 1 62369 62795 1 986134 1 4261

26001 3 62988 63392 1 990395 1 4041

26101 1 63595 63989 1 994436 1 3941

26201 3 64183 64558 1 998377 1 3751

26301 1 64733 65098 1 1002128 1 3651

26401 3 65258 65615 1 1005779 1 3571

26501 1 65790 66143 1 1009350 1 3531

26601 3 66666 67019 1 1012881 1 3531

26701 1 67204 67549 1 1016412 1 3451

26801 3 67737 68070 1 1019863 1 3331

26901 3 68376 68711 1 1023194 1 3351

27001 1 68865 69178 1 1026545 1 3131

27101 3 69315 69634 1 1029676 1 3191

27201 1 69786 70086 1 1032867 1 3001

27301 3 70227 70524 1 1035868 1 2971

27401 1 70669 70961 1 1038839 1 2921

27501 3 71098 71380 1 1041760 1 2821

27601 1 71524 71795 1 1044581 1 2711

27701 3 71939 72193 1 1047292 1 2541

27801 3 65320 65554 1 1049833 1 2341

27901 1 65694 65945 1 1052174 1 2511

28001 3 66094 66302 1 1054685 1 2081

28101 1 66456 66683 1 1056766 1 2271

28201 3 66822 67024 1 1059037 1 2021

28301 1 67173 67378 1 1061058 1 2051

28401 3 67523 67710 1 1063109 1 1871

28501 1 67869 68052 1 1064980 1 1831

28601 3 68401 68573 1 1066811 1 1721

28701 1 68744 68932 1 1068532 1 1881

28801 3 69080 69242 1 1070413 1 1621

28901 1 67499 67657 1 1072034 1 1581

29001 3 67196 67341 1 1073615 1 1451

29101 1 66922 67069 1 1075066 1 1471

29201 3 66623 66757 1 1076537 1 1341

29301 1 66378 66502 1 1077878 1 1241

29401 3 66085 66198 1 1079119 1 1131

29501 1 65859 65964 1 1080250 1 1051

29601 3 65590 65688 1 1081301 1 981

29701 1 65366 65451 1 1082282 1 851

29801 3 65114 65195 1 1083133 1 811

29901 1 64875 64957 1 1083944 1 821

30001 3 64628 64714 1 1084765 1 861

30101 1 64392 64479 1 1085626 1 871

30201 3 64137 64219 1 1086497 1 821

30301 1 63912 63997 1 1087318 1 851

30401 3 63643 63726 1 1088169 1 831

30501 1 63416 63504 1 1089000 1 881

500101 2 69689 70298 1 1089881 1 6091

500201 4 70499 71137 1 1095972 1 6381

500301 2 71287 71903 1 1102353 1 6161

500401 4 72121 72720 1 1108514 1 5991

500501 2 58198 58428 1 1114505 1 2301

500601 4 58676 59021 1 1116806 1 3451

500701 2 59301 59707 1 1120257 1 4061

500801 4 59987 60479 1 1124318 1 4921

500901 2 60702 61280 1 1129239 1 5781

501001 4 61549 62211 1 1135020 1 6621

501101 2 62464 63217 1 1141641 1 7531

501201 1 70083 71005 1 1149172 1 9221

DIGITAL ARCHIVE DESCRIPTION OF GRID DATA

CLIENT U.S.G.S

NAME OF SURVEY AEROMAGNETIC SURVEY of **CALIFORNIA**

AREA NAME **DEATH VALLEY**

CONTRACTOR FUGRO AIRBORNE SURVEYS

JOB CODE 655

GRID ARCHIVE NAME CALIF_TF.GRD

FORMAT GEOSOFT BINARY GRID

CONTENT **TOTAL MAGNETIC INTENSITY**

CREATION DATE February 15, 2001

NUMBER of ROWS and COLUMNS 704 640

PIVOTAL POSITION (X,Y) 470022 3978828

CELL SIZE 133m

UNIT nT

UNIT FACTOR 0.001

MINIMUM VALUE (nT) -540.011

MAXIMUM VALUE (nT) 394.056

MEAN VALUE (nT) -101.347

GRID ARCHIVE NAME CALIF_RADAR.GRD

FORMAT GEOSOFT BINARY GRID

CONTENT **RADAR**

CREATION DATE March 7, 2001

NUMBER of ROWS and COLUMNS 704 640

PIVOTAL POSITION (X,Y) 470022 3978828

CELL SIZE 133m

UNIT m

UNIT FACTOR 0.01

MINIMUM VALUE (m) 168

MAXIMUM VALUE (m) 1217 (instrument maximum)

MEAN VALUE (m) 869

PROJECTION INFORMATION :

DATUM NAD83

SHEROID WGS84

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.