Acquisition and Processing Report · Fugro Airborne Surveys Pty Ltd. 7. FALCON. TM. Airborne...

De Grey and Yule

FALCONTM Airborne Gravity Gradiometer and Magnetic Geophysical Survey

Acquisition and Processing Report

Survey Flown: July 2009 to August 2009

By

FUGRO AIRBORNE SURVEYS Pty Ltd 435 Scarborough Beach Rd, Osborne Park

WA 6017 AUSTRALIA

FAS Job# 2054

koombeh

Text Box

Prepared for Department of Water, Government of Western Australia Level 4, 168 St George Tce, Perth, WA 6000.

Fugro Airborne Surveys Pty Ltd 2 FALCONTM Airborne Gravity Gradiometer, Magnetometer Survey – De Grey and Yule, WA, 2054

TABLE OF CONTENTS

1 INTRODUCTION .......................................................................................................................4

1.1 Survey Location ...................................................................................................................4 2 SUMMARY OF SURVEY PARAMETERS ..............................................................................6

2.1 Survey Area Specifications..................................................................................................6 2.2 Data Recording ....................................................................................................................9 2.3 Job Safety Plan.....................................................................................................................9

3 FIELD OPERATIONS ..............................................................................................................10 3.1 Operations ..........................................................................................................................10 3.2 Base Stations ......................................................................................................................10 3.3 Field Personnel...................................................................................................................10

4 QUALITY CONTROL RESULTS............................................................................................11 4.1 Survey acquisition issues ...................................................................................................11 4.2 Flight Path Maps ................................................................................................................11 4.3 Turbulence .........................................................................................................................12

4.3.1 De Grey ......................................................................................................................12 4.3.2 Yule............................................................................................................................13

4.4 Survey & System Noise .....................................................................................................14 4.5 Digital Terrain Model ........................................................................................................14 4.6 Terrain Clearance...............................................................................................................17

5 MAGNETIC RESULTS ............................................................................................................19 5.1 Processing Summary..........................................................................................................19 5.2 Magnetometer Data............................................................................................................19 5.3 Additional Processing ........................................................................................................19 5.4 Magnetic Images ................................................................................................................20

6 FALCONTM AIRBORNE GRAVITY GRADIENT (AGG) RESULTS ...................................22 6.1 Processing Summary..........................................................................................................22 6.2 FALCONTM Airborne Gravity Gradiometer Data .............................................................22 6.3 Radar Altimeter Data .........................................................................................................22 6.4 Laser Scanner Data ............................................................................................................22 6.5 Positional Data ...................................................................................................................23 6.6 Additional Processing ........................................................................................................23 6.7 FALCONTM Airborne Gravity Gradient Data - GDD & gD ................................................23

7 APPENDIX I - SURVEY EQUIPMENT ..................................................................................32 7.1 Survey Aircraft...................................................................................................................32 7.2 FALCONTM Airborne Gravity Gradiometer......................................................................32 7.3 Airborne Data Acquisition Systems...................................................................................32 7.4 Aerial and Ground Magnetometers....................................................................................32 7.5 Real-Time Differential GPS...............................................................................................33 7.6 GPS Base Station Receiver ................................................................................................33 7.7 Altimeters...........................................................................................................................33 7.8 Laser Scanner.....................................................................................................................33 7.9 Data Processing Hardware and Software...........................................................................33

8 APPENDIX III - SYSTEM TESTS...........................................................................................34 8.1 Instrumentation Lag ...........................................................................................................34 8.2 Radar Altimeter Calibration...............................................................................................34 8.3 FALCONTM AGG Noise Measurement.............................................................................34 8.4 Daily Calibrations ..............................................................................................................34

8.4.1 Magnetic Base Station Time Check...........................................................................34 8.4.2 FALCONTM AGG Calibration...................................................................................34

9 APPENDIX IV - FALCONTM AGG DATA & PROCESSING................................................35


9.1 Nomenclature .....................................................................................................................35 9.2 Units ...................................................................................................................................35 9.3 FALCON Airborne Gravity Gradiometer Surveys............................................................35 9.4 Gravity Data Processing.....................................................................................................35 9.5 Aircraft dynamic corrections .............................................................................................36 9.6 Self Gradient Corrections...................................................................................................36 9.7 Laser Scanner Processing...................................................................................................36 9.8 Terrain Corrections ............................................................................................................36 9.9 Tie-line Levelling...............................................................................................................37 9.10 Transformation into GDD & gD...........................................................................................37 9.11 Noise & Signal ...................................................................................................................38 9.12 Risk Criteria in Interpretation ............................................................................................38 9.13 References..........................................................................................................................39

10 APPENDIX IV - FINAL PRODUCTS..................................................................................40 Table 1 Final MAG Digital Data – Geosoft Database Format ......................................................40 Table 2 Final FALCONTM AGG Digital Data – Geosoft Database Format ..................................43

11 APPENDIX IV - Final Line Listing ......................................................................................44 12 APPENDIX IV - Survey Production Report..........................................................................45

FIGURES

Figure 1: De Grey - Survey Area Location ..........................................................................................4 Figure 2: Yule - Survey Area Location ................................................................................................5 Figure 3: Flight Path maps ................................................................................................................12 Figure 4: De Grey - Turbulence (milli g) ...........................................................................................13 Figure 5: Yule - Turbulence (milli g).................................................................................................14 Figure 6: De Grey - Final Digital Terrain Model (metres above WGS84 ellipsoid with EGM96

geoid correction)........................................................................................................................15 Figure 7: Yule - Final Digital Terrain Model (metres above WGS84 ellipsoid with EGM96 geoid

correction)..................................................................................................................................16 Figure 8: De Grey - Survey clearance (metres above ground surface) .............................................17 Figure 9: Yule - Survey clearance (metres above ground surface) ...................................................18 Figure 10: Magnetometer Data Processing .......................................................................................19 Figure 11: De Grey – Total Magnetic Intensity (nT) .........................................................................20 Figure 12: Yule – Total Magnetic Intensity (nT) ...............................................................................21 Figure 13: FALCONTM AGG Data Processing ..................................................................................22 Figure 14: De Grey – Fourier Domain GDD (Eö), 8000 m cut-off wavelength. .................................24 Figure 15: De Grey – Equivalent Source GDD (Eö). ..........................................................................25 Figure 16: Yule – Fourier Domain GDD (Eö), 8000 m cut-off wavelength. .......................................26 Figure 17: Yule – Equivalent Source GDD (Eö). ................................................................................27 Figure 18: De Grey – Vertical Gravity (gD) from Fourier processing (mGal). .................................28 Figure 19: De Grey – Vertical Gravity (gD) from Equivalent Source (mGal). ..................................29 Figure 20: Yule – Vertical Gravity (gD) from Fourier processing (mGal)........................................30 Figure 21: Yule – Vertical Gravity (gD) from Equivalent Source (mGal). ........................................31


1 INTRODUCTION Fugro Airborne Surveys Pty Ltd conducted a high-sensitivity aeromagnetic and FALCONTM

Airborne Gravity Gradiometer (AGG) survey over the De Grey and Yule survey areas within the Pilbara region of Western Australia, Australia under contract with the Western Australia Department of Water The survey was flown from Port Hedland International Airport, Western Australia

1.1 Survey Location The De Grey survey area is located at longitude 119º 23’E, 20º 10’S (see the location map in 1). The Yule survey area is located at longitude 118º 11’E, 20º 28’S (see the location map in 1). Figure 1 shows the geographical position of the survey areas. The production flights took place from July 2009 to August 2009. 10 production flights were flown, for a total of 1,246 kilometres, to complete the two planned survey areas.

Figure 1: De Grey - Survey Area Location


Figure 2: Yule - Survey Area Location


2 SUMMARY OF SURVEY PARAMETERS 2.1 Survey Area Specifications De Grey Total Area kilometres (km) 1013 Terrain Clearance (m) 80 Clearance Method Drape Traverse Line Direction (deg.) 054 / 234 Traverse Line Spacing (m) 4000 Tie Line Direction (deg.) 144 / 324 Tie Line Spacing (m) 30000


The survey block is defined by the following coordinates in UTM zone 50S, referenced to the WGS84 datum:

WGS84, SUTM50 Block Name Corner Number UTM East UTM North De Grey A 730633 7726565 B 699818 7769352 C 703140 7771152 D 706095 7773878 E 707015 7777934 F 708123 7783332 G 712690 7784301 H 716012 7785131 I 718503 7787623 J 718365 7790529 K 721272 7791083 L 724870 7788730 M 725424 7786654 N 726947 7786377 O 726808 7788868 P 727639 7791360 Q 729715 7791775 R 732898 7791221 S 736912 7789560 T 748539 7787207 U 753245 7786930 V 755736 7785270 W 758366 7786100 X 760304 7784993 Y 759473 7783885 Z 768747 7777518 AA 773176 7778211 BB 774699 7779871 CC 776359 7780979 DD 779182 7782715 EE 780468 7785817 FF 789774 7791340 GG 795978 7789297 HH 802939 7779234 JJ 787958 7768263


Yule Total Area kilometres (km) 233 Terrain Clearance (m) 80 Clearance Method Drape Traverse Line Direction (deg) 070/ 250 Traverse Line Spacing(m) 4000 Tie Line Direction(deg) 160 / 340 Tie Line Spacing (m) 14000 The survey block is defined by the following coordinates in UTM zone 50S, referenced to the WGS84 datum: WGS84, SUTM50 Block Name Corner Number UTM East UTM North Yule A 627226 7726549 B 606584 7718762 C 6000056 7735835 D 602593 7735969 E 605532 7737638 F 608069 7739775 G 609204 7741712 H 611742 7742780 I 613812 7744316 J 617217 7746586 K 620556 7748923 L 622559 7751260 M 624162 7751260 N 624028 7750259 O 624496 7748790 P 624362 7748523 Q 623361 7749925 R 622760 7749658 S 623561 7747521 T 622359 7747454 U 622092 7746787 V 623494 7745918 W 623761 7745050 X 624963 7744984 Y 625564 7746186 Z 626833 7747588 AA 627901 7747521 BB 630639 7746720 CC 630439 7747721 DD 631035 7748573 EE 632976 7749124 FF 632375 7748189 GG 632709 7747454 HH 633778 7747321 JJ 634980 7748055 KK 635848 7748055


LL 635914 7746787 MM 636449 7747120 NN 636449 7748122 OO 637116 7747788 PP 636782 7748723 QQ 636782 7749591 RR 634512 7749458 SS 635581 7750192 TT 637050 7750392 UU 638252 7750259 VV 638786 7750726 WW 645334 7733305 2.2 Data Recording The following parameters were recorded during the course of the survey: • FALCONTM AGG data: recorded at different intervals. • Airborne total magnetic field: recorded with a 0.1 s sampling rate; • Aircraft altitude: measured by the barometric altimeter at intervals of 0.1 s; • Terrain clearance: provided by the radar altimeter at intervals of 0.1 s; • Airborne GPS positional data (latitude, longitude, height, time and raw range from each satellite being tracked): recorded at intervals of 1 s; • Time markers: in digital data; • Ground total magnetic field: recorded with a 1 s sampling rate; • Ground based GPS positional data (latitude, longitude, height, time and raw range from each satellite being tracked): recorded at intervals of 1 s; • Aircraft distance to ground in different angular position: measured by the laser scanner system at intervals of 0.05 s; 2.3 Job Safety Plan A Job Safety Plan and Job Safety Analysis was prepared and implemented in accordance with the Fugro Airborne Surveys Occupational Safety and Health Management System.


3 FIELD OPERATIONS 3.1 Operations Air operations were conducted from Port Hedland International Airport. The field offices were set up in room D02 at Camp Kooyong, and room 17 at the Hospitality Inn, Port Hedland. 3.2 Base Stations The GPS base duel frequency, backup single frequency stations and magnetometer base stations were set up away from any cultural interference as detailed below. The differentially corrected WGS-84 coordinates of the GPS ground station were: GPS Base Station

Camp Kooyong – 24 to 31 July 2008: Latitude: 20° 22’ 48.51142” S Longitude: 118° 38’ 11.78337” E Height: 11.463 m Location: On roof above the door at Block D Room 2.

Hospitality Inn – 1 to 3 August 2008: Latitude: 20° 18’ 33.51074” S Longitude: 118° 36’ 23.08386” E Height: 12.473 m Location: Outside the back of room 17.

Mag Base Station (CF1)

Latitude: 20° 22’ 38.26480” S Longitude: 118° 38’ 17.84967” E Location: Approx. 600 m north of Camp Kooyong on a mudflat. Base: 51929 nT

3.3 Field Personnel The following technical personnel participated in field operations: Crew Leader: B.Sun Geophysicist: D.Gay Pilot: T.Miller Technicians: B. Sun, T.Waumsley


4 QUALITY CONTROL RESULTS 4.1 Survey acquisition issues Several landowners in the survey areas were contacted prior to operations. Landowners at De Grey Station were contacted daily to organize the survey around mustering activity. Mine operators at the Atlas Iron Ltd mine site were contacted daily to organize the survey around blasting activity. Strong 30 knot NE winds hampered operations constantly, buffeting the aircraft continuously.

4.2 Flight Path Maps

Although not apparent from the survey flight path there was a sharp turn and climb at the eastern end of line 1000210. This turn was commenced outside the survey boundary. However there is a noticeable jump in the A and B components at the end of the line. There is no obvious impact on computed gravity gradient products.


Figure 3: Flight Path maps

4.3 Turbulence

4.3.1 De Grey The mean turbulence was 69.8 milli g. Average turbulence was somewhat high due to the very strong winds experienced during the course of the survey. The turbulence pattern across the survey area is shown in Figure 4.


Figure 4: De Grey - Turbulence (milli g)

4.3.2 Yule The mean turbulence was 60.6 milli g. Average turbulence was somewhat high due to the very strong winds experienced during the course of the survey. The turbulence pattern across the survey area is shown in Figure 4.


Figure 5: Yule - Turbulence (milli g)

4.4 Survey & System Noise The survey and system noise, defined to be the RMS (root mean square) noise in the GUV and GNE curvature components, was computed to be 5.95 Eö and 5.64 Eö for De Grey and 4.40 Eö and 3.94 Eö for Yule.

4.5 Digital Terrain Model For both areas, good quality DGPS data resulted in very little striping from line to line in the laser scanner derived DTM. Cross over difference grids of the survey lines and tie lines were checked and no adjustment of individual lines was required. Laser scanner data were gridded at 25m with a 1 cell maximum extension beyond data limits then filled and buffered out to 15kms beyond the survey boundaries using Shuttle Radar Topography


Mission (SRTM) v2 data. The stitching operation was carried out using v4 of the proprietary ERMapper DTM wizard. The wizard uses the Laser scanner data to locally adjust the SRTM prior to stitching.

Figure 6: De Grey - Final Digital Terrain Model (metres above WGS84 ellipsoid with EGM96 geoid correction)


Figure 7: Yule - Final Digital Terrain Model (metres above WGS84 ellipsoid with EGM96 geoid correction)


4.6 Terrain Clearance Terrain clearance was within 10m of the nominal survey height of 80m for most of the survey areas (see Figure 8 & 9). For De Grey, 98% of the data was within +/- 10 m of the nominal survey height and for Yule 99% of the data was within +/- 10 m of the nominal survey height.

Figure 8: De Grey - Survey clearance (metres above ground surface)


Figure 9: Yule - Survey clearance (metres above ground surface)


5 MAGNETIC RESULTS

5.1 Processing Summary

Mag Processing Flow Chart

Figure 10: Magnetometer Data Processing

All preliminary data compilation such as editing and filtering was performed in the field. Preliminary processing for on-site quality control was performed as each flight was completed. Final data processing was performed at Fugro head office in Perth. 5.2 Magnetometer Data Figure 9 summarises the steps involved in processing the magnetic data obtained from the survey. The airborne magnetometer data, recorded at 10 Hz, were plotted and checked for spikes and noise. Ground magnetometer data, recorded at 1 Hz, were de-spiked and filtered. The airborne magnetometer data were then corrected for diurnal variations by subtracting the filtered diurnal data and then adding back the average ground station value. Following this the data is then corrected for system lag / parallax. An IGRF correction is then applied to each point using the IGRF 2005 model.

5.3 Additional Processing No tie levelling or micro levelling was required.

Raw Base Mag Data (1Hz) Airborne Compensated Mag Data (10Hz)

Despiked and Filtered Checked and Despiked if necessary

Diurnal Correction applied

Mag Corrected for Lag / Parallax

IGRF Correction Applied

Diurnal and IGRF Corrected Magnetics


5.4 Magnetic Images

Figure 11: De Grey – Total Magnetic Intensity (nT)


Figure 12: Yule – Total Magnetic Intensity (nT)


6 FALCONTM AIRBORNE GRAVITY GRADIENT (AGG) RESULTS

6.1 Processing Summary

FALCONTM AGG Processing Flow Chart

Figure 13: FALCONTM AGG Data Processing

6.2 FALCONTM Airborne Gravity Gradiometer Data The FALCONTM Airborne Gravity Gradiometer data were digitally recorded by the ADAS on removable hard drives. The raw data were then copied on to the field processing laptop, backed up twice onto DVD+R media and then shipped to Fugro Perth using a secure courier service. Preliminary processing and QC of the FALCONTM AGG data is completed on-site by the data processor using Fugro’s DiAGG software. Further QC and Final FALCONTM AGG data processing is performed by the data processor located in either Perth or Melbourne, Australia. 6.3 Radar Altimeter Data The terrain clearance measured by the radar altimeter in metres was recorded at 10Hz. The data were plotted and inspected for quality. 6.4 Laser Scanner Data The terrain clearance measured by the laser scanner in metres was recorded at 20 scans/sec. The laser scanner data was verified by scanning the angle range of -2° to 2°, and by comparing to radar

Flights (Laser data) merged

AGG data sub sampled to 8hz

DGPS imported

PMC Calculated & Applied

S & T Corrections Applied

Tie line levelled data

Transformation to gD/GDD

DTM grid @ 25m cell size

AGG 8hz imported

Laser data QCed AGG data QCed

Flights (AGG data) merged

Self gradient (S) calculated

Terrain Effects (T) calculated DTM/regional SRTM merged

Demodulation (0.18 Hz)

Demodfilter / Modulation (0.18hz)

Laser Scanner sub sampled

Laser imported


and DGPS altitudes. 6.5 Positional Data A number of programs were executed for the compilation of navigation data in order to reformat and recalculate positions in differential mode. Waypoint’s GrafNav GPS processing software was used to calculate DGPS positions from raw range data obtained from the moving (airborne) and stationary (ground) receivers. The GPS ground station position was determined by logging GPS data continuously for 24 hr prior to survey flights commencing. The GPS data was processed and quality controlled completely in the field. Positional data (X, Y, Z) were recorded in the WGS84 datum and were not transformed. At mapping scales, WGS-84 is indistinguishable from the GDA94 datum. Parameters for the datum are:

Ellipsoid: WGS84 Semi-major axis: 6378137.0 m 1/flattening: 298.257

6.6 Additional Processing For both areas the AGG data were processed with densities of 0.00 and 2.67 g/cm3. Line channel data includes products at both densities. Final grid products of 2.67 g/cm3 only were made.

6.7 FALCONTM Airborne Gravity Gradient Data - GDD & gD The transformation into GDD and gD was accomplished using two methods: Fourier domain transformation and the Method of Equivalent Sources. Fourier Fourier products were produced at 0.00 and 2.67 g/cm3 terrain correction densities as described above using a cut-off wavelength of 8000 m (~2 x line spacing). Equivalent Source For both areas it was possible to closely match the wavelength characteristics of the Fourier products by placing the sources at a depth of 8000 metres. The different GDD maps are shown in Figures 14 to 17 respectively.


Figure 14: De Grey – Fourier Domain GDD (Eö), 8000 m cut-off wavelength.


Figure 15: De Grey – Equivalent Source GDD (Eö).


Figure 16: Yule – Fourier Domain GDD (Eö), 8000 m cut-off wavelength.


Figure 17: Yule – Equivalent Source GDD (Eö).

Two versions of vertical gravity (gD) are presented, deriving from integration of the GDD from the Fourier and Equivalent Source methods respectively. Fourier results are presented in Figures 18 and 19. The Equivalent Source results are presented in Figures 20 and 21. As discussed in section 9.10, it is not possible to accurately reconstruct long wavelength information in gD without incorporating ancillary information. There are significant long wavelength trend differences between the Fourier and Equivalent Source vertical gravity products (gD). The equivalent source and Fourier methods handle long wavelengths in a different manner and the long wavelength behaviour of the Fourier product differs slightly from the Equivalent Source version.


Figure 18: De Grey – Vertical Gravity (gD) from Fourier processing (mGal).


Figure 19: De Grey – Vertical Gravity (gD) from Equivalent Source (mGal).


Figure 20: Yule – Vertical Gravity (gD) from Fourier processing (mGal).


Figure 21: Yule – Vertical Gravity (gD) from Equivalent Source (mGal).


7 APPENDIX I - SURVEY EQUIPMENT 7.1 Survey Aircraft Cresco PAC (VH-KPY) The Cresco PAC registered VH-KPY, was used to fly the survey. This aircraft is powered with a Pratt & Witney PT6AG34 engine of 750 shp (560kW). The PAC offers the highest performance in its category with enhanced safety and reduced pilot workload. With a total load capacity of 3242kg, and a high rate of climb (1560 ft/min at sea level), this aircraft is ideal for transporting heavy loads. The aircraft is fitted with a special stinger to mount and house the magnetometer sensor. Extensive modifications have been made to accommodate the FALCONTM AGG system. 7.2 FALCONTM Airborne Gravity Gradiometer Feynman FALCONTM DAGG System The FALCONTM DAGG System is based on existing gravity gradiometer technology and has been optimized for airborne mineral exploration. The system is capable of supporting surveying activities in areas ranging from 1,000 ft below sea level to 13,000 ft above sea level with aircraft speeds from 70 to 130 knots. The FALCONTM AGG data streams were digitally recorded at different rates on removable drives installed in the FALCONTM AGG electronics rack. 7.3 Airborne Data Acquisition Systems Fugro Digital Acquisition System (FASDAS) The Fugro FASDAS is a data acquisition system executing propriety software for the acquisition and recording of location, magnetic and ancillary data. Data are presented both numerically and graphically in real time on the VGA display providing on-line quality control capability. The FASDAS is also used for real time navigation. A pre-programmed flight plan containing boundary coordinates, line start and end coordinates, local coordinate system parameters, line spacing and cross track definitions is loaded into the computer prior to each flight. The WGS-84 latitude and longitude received from the dual frequency Novatel OEMV L-Band Positioning receiver, is transformed to the local coordinate system for cross track and distance to go values. This information, together with ground heading and speed, is displayed to the pilot numerically and graphically on a two line LCD display. It is also presented on the operator LCD screen in conjunction with a pictorial representation of the survey area, survey lines and ongoing flight path. FALCONTM AGG Data Acquisition System (ADAS) The Fugro DAS provides control and data display for the FALCONTM AGG system. Data is displayed real time for the operator and warnings displayed should system parameters deviate from tolerance specifications. All FALCONTM AGG and laser scanner data are recorded to a removable hard drive. 7.4 Aerial and Ground Magnetometers Geometrics 822A Caesium Magnetometer The airborne Caesium magnetometer is a Geometrics 822A having a noise envelope of 0.002nT pk-pk in 0.01-1Hz bandwidth. The ground magnetometer was a CF1 Caesium sensor sampling at 1Hz.


7.5 Real-Time Differential GPS Novatel OEMV L-Band Positioning The Novatel OEMV L-band Positioning receiver provides real-time differential GPS for the onboard navigation system. The differential data set was relayed via a geo-synchronous satellite serving Australia, to the aircraft where the receiver optimized the corrections for the current location. 7.6 GPS Base Station Receiver Novatel OEM4 L1/L2 The Novatel GPS receiver is a 12 channel dual frequency GPS receiver. It provides raw range information of all satellites in view sampled every 1s and recorded on a computer laptop. This data is post-processed with the rover data to provide differential GPS (DGPS) corrections for the flight path. 7.7 Altimeters Sperry Stars AA-200Radar Altimeter Fugro Digital Barometric Pressure Sensor The radar altimeter has a resolution of 1m, an accuracy of 2%, a range of 1-2,500 ft and a measurement rate of 10 Hz. The barometric pressure is measured with an on board pressure module (Rosemount 1241M) with a suitable pneumatic connection to a pito-static system. 7.8 Laser Scanner Riegl LMS-Q140I-80 The laser scanner is designed for high speed line scanning applications. The system is based upon the principle of time-of-flight measurement of short laser pulses in the infrared wavelength region and the angular deflection of the laser beam is obtained by a rotating polygon mirror wheel. The measurement range is up to 500m with a minimum range of 2 m and an accuracy of 50mm. The laser beam is eye safe, the laser wavelength is 0.9 μm, the scan angle range is 158° and the speed is 20 scans/s. 7.9 Data Processing Hardware and Software The following equipment was used in the field office: Hardware

• One Dell Latitude D820, 2.0 GHz laptop computer • One Toshiba Satellite Pro 4600 Laptop • External USB hard drive reader for ADAS removable drives • External USB hard drive for data backup • HP DeskJet F2180 All-In-One printer, copier, scanner

Software

• Oasis Montaj data processing and imaging software • GrafNav Differential GPS processing software • Fugro - Atlas data processing software • Fugro - DiAGG Processing software


8 APPENDIX III - SYSTEM TESTS 8.1 Instrumentation Lag Due to the relative position of the magnetometer, crystal packs, altimeters and GPS antenna on the aircraft and to processing/recording time lags, raw readings from each vary in position. To correct for this and to align selected anomaly features on lines flown in opposite directions, the magnetics and altimeter data are ‘parallaxed’ with respect to the position information. The lag was applied to the magnetic data during processing. 8.2 Radar Altimeter Calibration The radar altimeter is checked for accuracy and linearity every 12 months, or when any change in a key system component requires this procedure to be carried out. This calibration allows the radar altimeter data to be compared and assessed with the other height data (GPS, barometric and laser) to confirm the accuracy of the radar altimeter over its operating range. The calibration is performed by flying a line at constant gradient over the ocean and using the results of the radar altimeter, differentially corrected GPS heights in mean sea level (MSL) and laser scanner were used to derive slope and offset information. A calibration flight was carried out in May 2008, over the Jandakot, WA. 8.3 FALCONTM AGG Noise Measurement At the commencement of the survey, 20 minutes of data were collected with the aircraft in straight level flight at 3500ft AGL. This data was processed as a survey line to check the AGG noise levels. Daily flight debriefs incorporating FALCONTM AGG performance statistics for each flight line are prepared using output from Fugro DiAGG software. These are sent daily to Fugro Perth staff for performance evaluation. 8.4 Daily Calibrations A set of daily calibrations were performed each survey day as follows: Magnetic base station time check AGG Quiescent Calibration

8.4.1 Magnetic Base Station Time Check Prior to each days survey all magnetic base stations were time checked and synchronised with the time on the aircraft survey system GPS receiver.

8.4.2 FALCONTM AGG Calibration

A calibration was performed at the beginning of each flight and the results monitored by the operator. The coefficients obtained from each of the calibrations were used in the processing of the data.


9 APPENDIX IV - FALCONTM AGG DATA & PROCESSING

9.1 Nomenclature The Falcon airborne gravity gradiometer (AGG) system adopts a North, East, and Down coordinate sign convention and these directions (N, E, and D) are used as subscripts to identify the gravity gradient tensor components. Lower case is used to identify the components of the gravity field and upper case to identify the gravity gradient tensor components. Thus the parameter usually measured in a normal exploration ground gravity survey is gD and the vertical gradient of this component is GDD.

9.2 Units The vertical component of gravity (gD) is delivered in the usual units of mGal. The gradient tensor components are delivered in Eötvös, which is usually abbreviated to “Eö”. By definition 1 Eö = 10-4 mGal/m.

9.3 FALCON Airborne Gravity Gradiometer Surveys In standard ground gravity surveys, the component measured is “gD”, which is the vertical component of the acceleration due to gravity. In airborne gravity systems, since the aircraft is itself accelerating, measurement of “gD” cannot be made to the same precision and accuracy as on the ground. Airborne gravity gradiometry uses a differential measurement to remove the aircraft motion effects and delivers gravity data of a spatial resolution and sensitivity comparable with ground gravity data. The Falcon gradiometer instrument acquires two curvature components of the gravity gradient tensor namely GNE and GUV where GUV = (GEE – GNN)/2. Since these curvature components cannot easily and intuitively be related to the causative geology, they are transformed into the vertical gravity gradient (GDD), and integrated to derive the vertical component of gravity (gD). Interpreters display, interpret and model both GDD and gD. The directly measured GNE and GUV data are appropriate for use in inversion software to generate density models of the earth. The vertical gravity gradient, GDD, is more sensitive to small or shallow sources and has greater spatial resolution than gD (similar to the way that the vertical gradient provides greater spatial resolution and increased sensitivity to shallow sources of the magnetic field). In the integration of GDD to give gD, the very long wavelength component, at wavelengths comparable to or greater than the size of the survey area, cannot be fully recovered. Long wavelength gravity are therefore incorporated in the gD data from other sources. This might be regional ground, airborne or marine gravity if such data are available. The Danish National Space Centre global gravity data of 2008 (DNSC08) are used as a default if other data are not available.

9.4 Gravity Data Processing The main elements and sequence of processing of the gravity data are as follows: 1. Dynamic corrections for residual aircraft motion (called Post Mission Compensation or PMC)

are calculated and applied. 2. Self Gradient corrections are calculated and applied to reduce the time-varying gradient

response from the aircraft and platform. 3. A Digital Terrain Model (DTM) is created from the laser scanner range data, the AGG inertial

navigation system rotation data and the DGPS position data. 4. Terrain corrections are calculated and applied.


5. GNE and GUV are levelled and transformed into the full gravity gradient tensor, including GDD, and into gD.

9.5 Aircraft dynamic corrections The design and operation of the FALCON AGG results in very considerable reduction of the effects of aircraft acceleration but residual levels are still significant and further reduction is required and must be done in post-processing. Post-processing correction relies on monitoring the inertial acceleration environment of the gravity gradiometer instrument (GGI) and constructing a model of the response of the GGI to this environment. Parameters of the model are adjusted by regression to match the sensitivity of the GGI during data acquisition. The modelled GGI output in response to the inertial sensitivities is subtracted from the observed output. Application of this technique to the output of the GGI, when it is adequately compensated by its internal mechanisms, reduces the effect of aircraft motion to acceptable levels. Following these corrections, the gradient data are demodulated and filtered along line with a 6-pole Butterworth low-pass filter with a cut-off frequency of 0.18 Hz (for fixed-wing operations; a higher frequency may be used for helicopter operations).

9.6 Self Gradient Corrections The GGI is mounted in gimbals controlled by an inertial navigation system which keeps the GGI pointing in a fixed direction whilst the aircraft and gimbals rotate around it. Consequently, the GGI measures a time-varying gravity gradient due to these masses moving around it as the heading and attitude of the aircraft changes during flight. This is called the self-gradient. Like the aircraft dynamic corrections, the self-gradient is calculated by regression of model parameters against measured data. In this case, the rotations of the gimbals are the input variables of the model. Once calculated, the modelled output is subtracted from the observed output.

9.7 Laser Scanner Processing The laser scanner measures the range from the aircraft to the ground in a swathe of angular width ±40 degrees below the aircraft. The aircraft attitude (roll, pitch and heading) data provided by the AGG inertial navigation system are used to adjust the range data for changes in attitude and the processed differential GPS data are used to reference the range data to located ground elevations referenced to the WGS 84 datum. Statistical filtering strategies are used to remove anomalous elevations due to foliage or built environment. The resulting elevations are gridded to form a digital terrain model (DTM).

9.8 Terrain Corrections An observation point above a hill has excess mass beneath it compared to an observation point above a valley. Since gravity is directly proportional to the product of the masses, uncorrected gravity data have a high correlation with topography. It is therefore necessary to apply a terrain correction to gravity survey data. For airborne gravity gradiometry at low survey heights, a detailed DTM is required. Typically, immediately below the aircraft, the digital terrain will need to be sampled at a cell size roughly one-third to one-half of the


survey height and with a position accuracy of better than 1 metre. For these accuracies, LIDAR data are required and each FALCON survey aircraft comes equipped with LIDAR (laser scanner). The laser scanner data only provide elevations in a swathe under each flight line. At low altitudes and with wide line spacing, gaps in the elevation data will exist between lines. Over areas flown at ground clearance greater than the laser range and water surfaces with poor dispersion, there will also be gaps in the surface elevation information. Finally for a good terrain correction, elevation data from outside the survey area are required. For this reason, the elevations from the laser scanner are merged with other elevation data. Almost always these are shuttle radar topography mission (SRTM) data. Although the SRTM data are inadequate for terrain corrections directly under the aircraft where the surface is closest to the aircraft, it is sufficiently accurate for terrain corrections at greater distance from the aircraft such as between swathes or outside the survey area. Water surfaces are treated as flat from the mapped shorelines. If bathymetric data are used then these form a separate terrain model for which terrain corrections are calculated at a density chosen to suit the water bottom – water interface. Once the DTM has been merged, the terrain corrections for each of the GNE and GUV data streams are calculated. In the calculation of terrain corrections, a density of 1 gm/cc is used. The calculated corrections are stored in the database allowing the use of any desired terrain correction density by subtracting the product of desired density and correction from the measured GNE and GUV data. The terrain correction density is chosen to be representative of the terrain density over the survey area. density Sometimes more than one density is used with input from the client. Typically, the terrain corrections are calculated over a distance 10 km from each survey measurement point.

9.9 Tie-line Levelling The terrain- and self gradient-corrected GNE and GUV data are tie-line levelled across the entire survey using a least-squares minimisation of differences at survey line intersections. Occasionally some micro-levelling might be performed.

9.10 Transformation into GDD & gD The transformation of the measured, corrected and levelled GNE and GUV data into gravity and components of the full gravity gradient tensor is accomplished using two methods:

Fourier domain transformation and Equivalent source transformation.

The Fourier method relies on the Fourier transform of Laplace’s equation. The application of this transform to the complex function GNE + i GUV provides a stable and accurate calculation of each of the full tensor components and gravity. The Fourier method performs piece-wise upward and downward continuation to work with data collected on a surface that varies from a flat horizontal plane. For stability of the downward continuation, the data are low-pass filtered. The cut-off wavelength of this filter depends on the variations in altitude and the line spacing. It is set to the smallest value that provides stable downward continuation. The equivalent source method relies on a smooth model inversion to calculate the density of a surface of sources and from these sources, a forward calculation provides the GDD and gD data. The smoothing results in an output that is equivalent to the result of the low-pass filter in the Fourier domain method.


The Fourier method generates all tensor components but the equivalent source method only generates GDD and gD (and GNE and GUV for comparison with the inputs). The limitations of gravity gradiometry in reconstructing the long wavelengths of gravity can lead to differences in the results of these two methods at long wavelength. The merging of the gD data with externally supplied regional gravity such as the DNSC08 gravity removes these differences.

9.11 Noise & Signal With all the Falcon AGG instruments, there are two measurements made of both the NE and UV curvature components during acquisition. This gives a pair of independent readings at each sample point. The standard deviation of half the difference between these pairs is a good estimate of the survey noise. This is calculated for each line, and the average of all the survey lines is the figure quoted for the survey as a whole. This difference error has been demonstrated to follow a ‘normal’ or Gaussian statistical distribution, with a mean of zero. Therefore, the bulk of the population (95%) will lie between -2σ and +2σ of the mean. For a typical survey noise estimate of, say, 3 Eö, 95% of the noise will be between -6 Eö and +6 Eö. These typical errors in the curvature gradients translate to errors in GDD of about 5 Eö and in gD (in the shorter wavelengths) in the order of 0.1 mGal.

9.12 Risk Criteria in Interpretation

The risks associated with a Falcon AGG survey are mainly controlled by the following factors. • Survey edge anomalies – the transformation from measured curvature gradients to vertical gradient

and vertical gravity gradient is subject to edge effects. Hence any anomalies located within about 2 x line spacing of the edge of the survey boundaries should be treated with caution.

• Single line anomalies – for a wide-spaced survey, an anomaly may be present on only one line.

Although it might be a genuine anomaly, the interpreter should note that no two-dimensional control can be applied.

• Low amplitude (less than 2σ) anomalies – Are within the noise envelope and need to be treated

with caution, if they are single line anomalies and close in diameter to the cut-off wavelengths used.

• Residual topographic error anomalies – Inaccurate topographic correction either due to inaccurate DTM or local terrain density variations may produce anomalies. Comparing the DTM with the GDD map terrain-corrected for different densities is a reliable way to confirm the legitimacy of an anomaly.

• The low density of water and lake sediments (if present) can create significant gravity and gravity

gradient lows which may be unrelated to bedrock geology. It is recommended that all anomalies located within lakes or under water be treated with caution and assessed with bathymetry if available.


9.13 References

Lee, J. B., 2001, FALCON Gravity Gradiometer Technology, Exploration Geophysics, 32, 75-79.

Lee, J. B.; Liu, G.; Rose, M.; Dransfield, M.; Mahanta, A.; Christensen, A. and Stone, P., 2001, High resolution gravity surveys from a fixed wing aircraft, Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International, 3, 1327-1331.

Boggs, D. B. and Dransfield, M. H., 2004, Analysis of errors in gravity derived from the Falcon airborne gravity gradiometer, Lane, R. (ed.), Airborne Gravity 2004 - Abstracts from the ASEG-PESA Airborne Gravity 2004 Workshop, Geoscience Australia Record 2004/18, 135-141.

Dransfield, M. H. and Lee, J. B., 2004, The FALCON airborne gravity gradiometer survey systems, Lane, R. (ed.), Airborne Gravity 2004 - Abstracts from the ASEG-PESA Airborne Gravity 2004 Workshop, Geoscience Australia Record 2004/18, 15-19.

Dransfield, M. H. and Zeng, Y., Airborne gravity gradiometry: terrain corrections and elevation error, submitted to Geophysics.

Stone, P. M. and Simsky, A., 2001, Constructing high resolution DEMs from Airborne Laser Scanner Data, Preview, Extended Abstracts : ASEG 15th Geophysical Conference and Exhibition, August 2001, Brisbane., 93, 99.


10 APPENDIX IV - FINAL PRODUCTS Final MAG digital data consists of a 10Hz Geosoft Oasis GDB database file containing the fields and format described in Table 1 below. Final FALCONTM AGG digital data consists of a 8Hz Geosoft Oasis GDB database file containing the fields and format described in Table 2 below. No hardcopy products were delivered.

Field name Units Field label

EASTING m WGS84 UTM50S Easting

NORTHING m WGS84 UTM50S Northing

LONGITUDE dd.ddd WGS84 Longitude

LATITUDE dd.ddd WGS84 Latitude

ALTITUDE_Ellipsoid m Sensor Height above WGS84 ellipsoid

ALTITUDE m Sensor Height above WGS84 ellipsoid with Geoid (EGM96) correction applied

FIDUCIAL sec Fiducial (seconds) (UTC time since 1980)

RAWMAG nT Lagged uncompensated unfiltered uncorrected raw TMI

COMPMAG nT Lagged compensated uncorrected TMI

DIURNAL nT Diurnal

IGRF nT IGRF

DCMAG nT Compensated & diurnally corrected lagged TMI

LEVMAG nT Final processed and levelled TMI

LASER m Laser Altimeter, height above the ground

FLUX_X nT Fluxgate X component

FLUX_Y nT Fluxgate Y component

FLUX_Z nT Fluxgate Z component

Table 1 Final MAG Digital Data – Geosoft Database Format


Field name Field label Units

EASTING WGS84 UTM50S Easting metres NORTHING WGS84 UTM50S Northing metres LONGITUDE WGS84 Longitude degrees LATITUDE WGS84 Latitude degrees ALTITUDE_Ellipsoid Sensor Height above WGS84 ellipsoid (m) metres

ALTITUDE Sensor Height above WGS84 ellipsoid with Geoid (EGM96) correction applied (m) metres

FIDUCIAL Fiducial (seconds) (UTC time since 1980) seconds

fHEIGHT Flying height, (Aircraft's height above terrain) derived from laser scanner and ALTITUDE data (m) metres

DTM Terrain Height above WGS84 ellipsoid with Geoid (EGM96) correction applied (m) metres

TURBULENCE Estimated vertical platform turbulence (vertical acceleration where g = 9.80665 m/sec/sec) millig

Err_NE NE gradient uncorrelated noise estimate (Eötvös), after tieline levelling Eötvös

Err_UV UV gradient uncorrelated noise estimate (Eötvös), after tieline levelling Eötvös

T_DD Terrain effect calculated for DD using a density of 1g/cc Eötvös

T_NE Terrain effect calculated for NE using a density of 1g/cc Eötvös

T_UV Terrain effect calculated for UV using a density of 1g/cc Eötvös

A_SJT_2p67_NE

self gradient, jitter & terrain corrected NE gradient (Eötvös), terrain correction density 2.67 g/cc Eötvös

A_SJT_2p67_UV

self gradient, jitter & terrain corrected UV gradient (Eötvös), terrain correction density 2.67 g/cc Eötvös

B_SJT_2p67_NE


B_SJT_2p67_UV


G_SJT_2p67_NE


G_SJT_2p67_UV


A_SJT_0_NE self gradient & jitter corrected NE gradient (Eötvös), no terrain correction applied Eötvös

A_SJT_0_UV self gradient & jitter corrected UV gradient (Eötvös), no terrain correction applied Eötvös

B_SJT_0_NE self gradient & jitter corrected NE gradient (Eötvös), no terrain correction applied Eötvös

B_SJT_0_UV self gradient & jitter corrected UV gradient (Eötvös), no terrain correction applied Eötvös

G_SJT_0_NE self gradient & jitter corrected NE gradient (Eötvös), no terrain correction applied Eötvös

G_SJT_0_UV self gradient & jitter corrected UV gradient (Eötvös), no terrain correction applied Eötvös

gD_FOURIER_2p67

Fourier derived vertical Gravity (mGal), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength mGal

GEE_FOURIER_2p67

Fourier derived Gee gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös


GNN_FOURIER_2p67

Fourier derived Gnn gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

GDD_FOURIER_2p67

Fourier derived vertical gravity gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

GED_FOURIER_2p67

Fourier derived Ged horizontal EW gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

GND_FOURIER_2p67

Fourier derived Gnd horizontal NS gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

GNE_FOURIER_2p67

Fourier derived Gne curvature gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

GUV_FOURIER_2p67

Fourier derived Guv curvature gradient (Eötvös), terrain correction density 2.67 g/cc, 8000 m cut-off wavelength Eötvös

gD_FOURIER_0

Fourier derived vertical Gravity (mGal), no terrain correction applied, 8000 m cut-off wavelength mGal

GEE_FOURIER_0

Fourier derived Gee gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GNN_FOURIER_0

Fourier derived Gnn gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GDD_FOURIER_0

Fourier derived vertical gravity gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GED_FOURIER_0

Fourier derived Ged horizontal EW gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GND_FOURIER_0

Fourier derived Gnd horizontal NS gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GNE_FOURIER_0

Fourier derived Gne curvature gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

GUV_FOURIER_0

Fourier derived Guv curvature gradient (Eötvös), no terrain correction applied, 8000 m cut-off wavelength Eötvös

DRAPESURFACE_FOURIER Drape surface for Fourier reconstruction, Smoothed flight surface (m) metres

gD_EQUIV_2p67 Equivalent source derived vertical gravity (mGal), terrain correction density 2.67 g/cc mGal

GDD_EQUIV_2p67

Equivalent source derived vertical gravity gradient (Eötvös), terrain correction density 2.67 g/cc Eötvös

GNE_EQUIV_2p67 Equivalent source derived Gne curvature gradient (Eötvös), terrain correction density 2.67 g/cc Eötvös

GUV_EQUIV_2p67 Equivalent source derived Guv curvature gradient (Eötvös), terrain correction density 2.67 g/cc Eötvös

gD_EQUIV_0 Equivalent source derived vertical gravity (mGal), no terrain correction applied mGal

GDD_EQUIV_0 Equivalent source derived vertical gravity gradient (Eötvös), no terrain correction applied Eötvös

GNE_EQUIV_0 Equivalent source derived Gne curvature gradient (Eötvös), no terrain correction applied Eötvös

GUV_EQUIV_0 Equivalent source derived Guv curvature gradient (Eötvös), no terrain correction applied Eötvös

DRAPESURFACE_EQUIV Drape surface for equivalent source construction, 80 m above terrain (uses metres


Surface=Altitude-DTM)

Table 2 Final FALCONTM AGG Digital Data – Geosoft Database Format


11 APPENDIX IV - Final Line Listing De Grey and Yule Line# X-min X-max Y-min Y-max # of pts Total Distance (m)L1000210:3 706087 730044 7774066 7791762 4892 29833L1000310:8 702044 735257 7766179 7790297 5727 41049L1000410:8 704380 740175 7762936 7788947 8046 44254L1000510:8 706713 745501 7759698 7787873 6691 47944L1000630:10 709054 751259 7756448 7787096 9783 52168L1000710:8 711395 755673 7753199 7785371 7563 54740L1000810:8 713731 760008 7749955 7783576 10003 57208L1000920:8 716070 763499 7746701 7781174 8497 58637L1001010:1 718408 767008 7743459 7778768 8869 60084L1001110:6 720748 790785 7740211 7791055 12980 86553L1001210:6 723069 795417 7736986 7789533 14192 89427L1001310:5 725426 798003 7733716 7786453 13196 89725L1001420:9 727763 800276 7730472 7783169 13106 89649L1001520:9 730088 802551 7727237 7779880 15419 89579T1900110:8 706775 739070 7732649 7777094 8467 54946T1900210:9 733845 763316 7750319 7790882 7779 50144T1900310:9 777561 787565 7767979 7781771 2709 17039T1900310:9 777561 787565 7767979 7781771 2709 17039 L4000110:7 608154 632235 7740012 7749007 4597 25710L4000210:7 601064 639997 7733078 7747635 5881 41569L4000310:7 602482 641403 7729357 7743895 7319 41554L4000410:7 603918 642813 7725608 7740147 6012 41526L4000520:8 605342 644217 7721872 7736407 5820 41508T4900110:7 611775 619033 7723405 7742846 3089 20752T4900210:7 624879 632131 7728327 7747736 3458 20721


12 APPENDIX IV - Survey Production Report

Acquisition and Processing Report · Fugro Airborne Surveys Pty Ltd. 7. FALCON. TM. Airborne...

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