Magnetic Surveying and Anomalies

Question 1

The expected value of the field at any place is taken to be that of the

Answer 1

International Geomagnetic Reference Field (IGRF)

Question 2

• The difference between the observed and expected values is a magnetic anomaly

Answer 2

Magnetic Anomaly

Question 3

In land surveying, a portable magnetometer is used to measure the Earth’s surface magnetic field at grid points over a suspected geological structure
Though slow, this method yields a detailed pattern of the magnetic field anomaly due to close proximity measurements to the source

Answer 3

Land Surveying

Question 4

• Proton-precession magnetometers are most commonly used in

Answer 4

Land Surveying

Question 5

2 ways of Airborne Magnetic Surveying

Answer 5

1. the magnetometer may be mounted rigidly on the airplane at the end of a boom (“bird”)
2. towed in an aerodynamic housing behind the plane

Question 6

magnetometer must be towed some distance d behind the ship to escape its magnetic field

Answer 6

Shipborne Surveying

Question 7

• proton-precession magnetometer mounted in a waterproof “fish” is towed behind the ship at the end of a long cable

Answer 7

Shipborn Surveying

Question 8

consists of a pair of alkali-vapor magnetometers maintained at a fixed distance from each other

Answer 8

Magnetic gradiometers

Question 9

• includes parallel measurement lines and orthogonal cross-tie lines

Answer 9

The Survey Pattern

Question 10

• variation in intensity of the geomagnetic field at the Earth’s surface during the course of a day

Answer 10

Diurnal Variation

Question 11

Magnetic anomaly of an inclined magnetization
When an infinitely long dike is magnetized obliquely, its
anomaly can be modeled using __________

Answer 11

inclined dipole or pole distributions