Magnetic Methods and Results Daniel Boesner Wendy Key Geol 692 May 2009

Main Points Introduction Introduction Method Background and Theory Method Background and Theory Field Area Field Area Field Methods Field Methods Equipment Equipment Data Collection Data Collection Processing Processing Results Results Conclusions Conclusions

Method Background and Theory Magnetometer utilizes the precession of spinning protons to measure the total magnetic intensity of the Earth’s magnetic field. Magnetometer utilizes the precession of spinning protons to measure the total magnetic intensity of the Earth’s magnetic field. Values vary geographically due to the dipole nature of the Earth’s magnetic field. Values vary geographically due to the dipole nature of the Earth’s magnetic field. Iron-rich minerals and other metals produce localized perturbances in magnetic field values which are detected by the magnetometer. Iron-rich minerals and other metals produce localized perturbances in magnetic field values which are detected by the magnetometer. Simple model of the Earth’s magnetic field Proton procession magnetometer Breiner, S., 1973

Magnetic Contour Map Breiner, S., 1973

Iron-rich materials create perturbances in the magnetic field Effects of depth on anomaly on anomaly Breiner, S., 1973

Field Area Construction of the Truckee and V-Line Canals began in 1903 and 1904 respectively as part of The Newlands Project which used the combined waters of the Truckee and Carson Rivers to irrigate over 400,000 acres of western Nevada desert (Simond, 1996). Construction of the Truckee and V-Line Canals began in 1903 and 1904 respectively as part of The Newlands Project which used the combined waters of the Truckee and Carson Rivers to irrigate over 400,000 acres of western Nevada desert (Simond, 1996).

Field Methods-Equipment Scintrex Envi- Mag proton procession magnetometer Scintrex Envi- Mag proton procession magnetometer Roving and base station magneto- meters employed Roving and base station magneto- meters employed

Field Methods- Data Collection Total field data collected every 0.5 s by the rover and every 2 s by the base station. Total field data collected every 0.5 s by the rover and every 2 s by the base station. Stations were established at specified locations along 5 lines as follows: Stations were established at specified locations along 5 lines as follows: Lines 1 and 3 (Length of the V-line Canal and Truckee Canal): 100 m station intervals Lines 1 and 3 (Length of the V-line Canal and Truckee Canal): 100 m station intervals Lines 2 & 5 (Re-Evaluations): 25 m intervals Lines 2 & 5 (Re-Evaluations): 25 m intervals Line 3 (Abandoned Levee): 50 m intervals Line 3 (Abandoned Levee): 50 m intervals Stations were established to facilitate the collection of GPS locations and to allow for preliminary analysis of total field and noise anomalies in the field. Stations were established to facilitate the collection of GPS locations and to allow for preliminary analysis of total field and noise anomalies in the field.

Field Methods- Data Collection To better differentiate anomalies from observable cultural “contaminants” detailed maps were made locating cultural features. To better differentiate anomalies from observable cultural “contaminants” detailed maps were made locating cultural features. Anomalous areas were identified in the field by plotting total field measurements collected at each station. Anomalous areas were identified in the field by plotting total field measurements collected at each station.

Processing Oasis Montaje by Geosoft was used to evaluate the data. Oasis Montaje by Geosoft was used to evaluate the data. Position data between stations were calculated under the assumption that stations are the end points of a straight line. Position data between stations were calculated under the assumption that stations are the end points of a straight line. Noise values greater than 1 nT were removed in order to eliminate anomalies generated by noise sources. Noise values greater than 1 nT were removed in order to eliminate anomalies generated by noise sources. Data was reduced-to-pole (RTP) using an inclination of 63.5° and a declination of 14.21° (IGRF, NOAA). Data was reduced-to-pole (RTP) using an inclination of 63.5° and a declination of 14.21° (IGRF, NOAA).

Effects of Processing Raw Data Noise >1 nT Removed RTP

Results- V-Line Canal Line 2 Lines 1 and 3 Line 5

Results- Truckee Canal Line 4

Limitations A variety of surface and subsurface interpretations are possible for each recorded anomaly. A variety of surface and subsurface interpretations are possible for each recorded anomaly. Burger et al. (1992) suggest a distance of 20+ m should be maintained to reduce the effects of cultural “contaminants”. Burger et al. (1992) suggest a distance of 20+ m should be maintained to reduce the effects of cultural “contaminants”.

Conclusions Data anomalies may be unreliable due to the volume of cultural “contaminants” particularly along the Truckee Canal. Data anomalies may be unreliable due to the volume of cultural “contaminants” particularly along the Truckee Canal. Total field measurements along the Truckee Canal are more extreme than those along the V- Line Canal. Total field measurements along the Truckee Canal are more extreme than those along the V- Line Canal. Anomalies observed along the V-Line Canal could not be readily attributed to apparent cultural or geologic sources. Anomalies observed along the V-Line Canal could not be readily attributed to apparent cultural or geologic sources.

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 (Accessed: 26 April, 2009). Breiner, S., 1973, Applications manual for portable magnetometers: Sunnyvale, CA, Geometrics, 58.