Magnetic Methods and Magnetic Methods and ResultsResults

Daniel BoesnerDaniel Boesner

Wendy KeyWendy KeyGeol 692Geol 692 May 2009 May 2009

Main PointsMain Points

IntroductionIntroduction Method Background and TheoryMethod Background and Theory Field AreaField Area

Field MethodsField Methods EquipmentEquipment Data CollectionData Collection

ProcessingProcessing ResultsResults ConclusionsConclusions

Method Background and Method Background and TheoryTheory

Magnetometer utilizes the Magnetometer utilizes the precession of spinning protons to precession of spinning protons to measure the total magnetic measure the total magnetic intensity of the Earth’s magnetic intensity of the Earth’s magnetic field.field.

Values vary geographically due to Values vary geographically due to the dipole nature of the Earth’s the dipole nature of the Earth’s magnetic field.magnetic field.

Iron-rich minerals and other Iron-rich minerals and other metals produce localized metals produce localized perturbances in magnetic field perturbances in magnetic field values which are detected by the values which are detected by the magnetometer. magnetometer.

Simple model of the Earth’s magnetic field

Proton procession magnetometer

Breiner, S., 1973

Magnetic Contour MapMagnetic Contour Map

Breiner, S., 1973

Iron-rich Iron-rich materials create materials create perturbances in perturbances in the magnetic fieldthe magnetic field

Effects of depthEffects of depth on anomalyon anomaly

Breiner, S., 1973

Breiner, S., 1973

Field AreaField Area

Construction of the Construction of the Truckee and V-Line Truckee and V-Line Canals began in 1903 Canals began in 1903 and 1904 respectively and 1904 respectively as part of The as part of The Newlands Project which Newlands Project which used the combined used the combined waters of the Truckee waters of the Truckee and Carson Rivers to and Carson Rivers to irrigate over 400,000 irrigate over 400,000 acres of western acres of western Nevada desert Nevada desert (Simond, 1996).(Simond, 1996). http://www.waterhistory.org/histories/reclamation/newland/

Field Methods-EquipmentField Methods-Equipment Scintrex Envi-Scintrex Envi-

Mag proton Mag proton procession procession magnetometermagnetometer

Roving and Roving and base station base station magneto-magneto-meters meters employedemployed

Field Methods- Data Field Methods- Data CollectionCollection

Total field data collected every 0.5 s by the rover Total field data collected every 0.5 s by the rover and every 2 s by the base station.and every 2 s by the base station.

Stations were established at specified locations Stations were established at specified locations along 5 lines as follows:along 5 lines as follows: Lines 1 and 3 (Length of the V-line Canal and Truckee Lines 1 and 3 (Length of the V-line Canal and Truckee

Canal): 100 m station intervalsCanal): 100 m station intervals Lines 2 & 5 (Re-Evaluations): 25 m intervalsLines 2 & 5 (Re-Evaluations): 25 m intervals Line 3 (Abandoned Levee): 50 m intervalsLine 3 (Abandoned Levee): 50 m intervals

Stations were established to facilitate the Stations were established to facilitate the collection of GPS locations and to allow for collection of GPS locations and to allow for preliminary analysis of total field and noise preliminary analysis of total field and noise anomalies in the field. anomalies in the field.

Field Methods- Data Field Methods- Data CollectionCollection

To better To better differentiate differentiate anomalies from anomalies from observable cultural observable cultural “contaminants” “contaminants” detailed maps were detailed maps were made locating made locating cultural features.cultural features.

Anomalous areas Anomalous areas were identified in the were identified in the field by plotting total field by plotting total field measurements field measurements collected at each collected at each station.station.

ProcessingProcessing

Oasis Montaje by Geosoft was used to evaluate the Oasis Montaje by Geosoft was used to evaluate the data.data.

Position data between stations were calculated under Position data between stations were calculated under the assumption that stations are the end points of a the assumption that stations are the end points of a straight line.straight line.

Noise values greater than 1 nT were removed in Noise values greater than 1 nT were removed in order to eliminate anomalies generated by noise order to eliminate anomalies generated by noise sources.sources.

Data was reduced-to-pole (RTP) using an inclination Data was reduced-to-pole (RTP) using an inclination of 63.5of 63.5° and a declination of 14.21° (IGRF, NOAA).° and a declination of 14.21° (IGRF, NOAA).

Effects of ProcessingEffects of Processing

Raw DataRaw Data Noise >1 nTNoise >1 nTRemovedRemoved

RTPRTP

Results- V-Line CanalResults- V-Line Canal

Line 2Line 2

Lines 1 and 3Lines 1 and 3 Line 5Line 5

Results- Truckee CanalResults- Truckee Canal

Line 4Line 4

LimitationsLimitations

A variety of surface and subsurface A variety of surface and subsurface interpretations are possible for each recorded interpretations are possible for each recorded anomaly.anomaly.

Burger et al. (1992) suggest a distance of 20+ m Burger et al. (1992) suggest a distance of 20+ m should be maintained to reduce the effects of should be maintained to reduce the effects of cultural “contaminants”.cultural “contaminants”.

ConclusionsConclusions

Data anomalies may be unreliable due to Data anomalies may be unreliable due to the volume of cultural “contaminants” the volume of cultural “contaminants” particularly along the Truckee Canal.particularly along the Truckee Canal.

Total field measurements along the Total field measurements along the Truckee Canal are more extreme than Truckee Canal are more extreme than those along the V-Line Canal.those along the V-Line Canal.

Anomalies observed along the V-Line Anomalies observed along the V-Line Canal could not be readily attributed to Canal could not be readily attributed to apparent cultural or geologic sources.apparent cultural or geologic sources.

Questions?Questions?

References Burger, R.H., Sheehan, A.F., and Jones, C.H., 1992, Introduction to applied

geophysics: Exploring the shallow subsurface: New York, W.W. Norton & Company, 554 p.

Simonds, Wm., J., 1996, The Newlands Project: Third Draft: Bureau of Reclamation History Program <http://www.cityoffernley.org/index.asp?NID=339> (Accessed: 26 April, 2009).

Breiner, S., 1973, Applications manual for portable magnetometers: Sunnyvale, CA, Geometrics, 58.