Magnetics (M-11)

1. Q: How does it work?
   A: The earth's magnetic field induces a secondary magnetic field in ferrous materials. While all materials exhibit this susceptibility to a certain extent, iron and steel materials generally produce an effect that is easily measurable.
   

2. Q: What is the geologic model?
   A: Geologic materials with ferrous minerals (usually magnetite) are good targets. Manmade iron and steel items such as drums and tanks are often sought using measurements of the magnetic field.
   

3. Q: What are the requirements?
   A: A geologic structure or a manmade item with the right size and orientation to the earth's field such that the anomalous field can be detected. Interference takes the form of buildings and building foundations, fences, cars, known underground storage tanks, utilities, and landfill trash. Note that any one of these items may also be the target.
   

4. Q: What are the pitfalls?
   A: Magnetic storms in the earth's upper atmosphere can cause rapid variations in the inducing field, though the operation of a base station will allow the correction for most such variations. Ferrous materials, such as knives or belt buckles, carried by the magnetometer operator can contaminate the data. Many GPS units have a ferrite antenna making them unsuitable for use with a magnetometer. For many distributed anomalies, the shape of the anomaly is dipolar rather than bull's-eye shaped. Certain shapes and orientations of objects may produce outsized anomalies or almost no anomaly due to a combination of the orientation of the object with respect to the inducing field and the possibility of permanent remnant magnetization. In UXO (unexploded ordnance) work magnetic soils and magnetized float have proven to be a vexing problem.
   

5. Q: What logistics are needed?
   A: Crew size is usually one person. The magnetometer is self-contained and portable as is the base station if one is used.
   

6. Q: What are the deliverables?
   A: Maps of the survey location, color contour maps of the data acquired, residual-anomaly separation maps if necessary, and an interpretation map showing the cultural features and designated areas that are anomalous.
   
7. More detailed information.