chapter  8
Magnetometry, Self-Potential, and Seismic: Additional Geophysical Methods Having Potentially Signicant Future Use in Agriculture
Pages 16

Magnetometry is a passive remote sensing method that records the magnitude of Earth’s local magnetic eld at a sensor location. The Earth’s overall magnetic eld is a dipole eld with the North Magnetic Pole and the South Magnetic Pole acting much like the ends of a bar magnet. There are secondary regional and local variations to the primary dipole eld caused by soils and objects with different magnetic properties located above, on, or beneath the ground surface. Historically, the oersted and gamma have been the common units for measuring variations in Earth’s magnetic eld,

8.1 Magnetometry Methods ...................................................................................................... 147 8.1.1 Magnetometry Method Introduction ....................................................................... 147 8.1.2 Types of Magnetometers .......................................................................................... 148 8.1.3 Magnetometry Field Principles ................................................................................ 149 8.1.4 Magnetometry Data Processing and Analysis ......................................................... 149 8.1.5 Magnetometry Agricultural Application Example .................................................. 151

8.2 Self-Potential Methods ........................................................................................................ 152 8.2.1 Self-Potential Method Introduction ......................................................................... 152 8.2.2 Sources of Consistent and Unidirectional Natural Electric Potential Gradients ..... 153 8.2.3 Self-Potential Equipment, Field Procedures, and Data Analysis Products ............. 153 8.2.4 Possible Agricultural Applications for Self-Potential Methods ............................... 155

8.3 Seismic Methods ................................................................................................................. 155 8.3.1 Seismic Method Introduction ................................................................................... 155 8.3.2 Seismic Wave Types................................................................................................. 156 8.3.3 Aspects of Seismic Wave Propagation ..................................................................... 157 8.3.4 Seismic Method Data Collection, Data Analysis, and Potential Agricultural

Applications ............................................................................................................. 160 References ...................................................................................................................................... 161

and some of the older magnetometry data are displayed in these units. However, more recently, the common geophysical unit of measure for a magnetic eld is called a tesla, where one tesla is equal to 104 oersteds, or 109 gammas. The Earth’s magnetic eld intensity varies between 0.25 and 0.65 oersteds (25,000 to 65,000 nanoteslas [nT], or 25,000 to 65,000 gammas).