Explain how a marine magnetometer detects ferrous objects by measuring disturbances in the Earth's background magnetic field, and identify the three main instrument types used in marine survey practice.

Describe the operational procedures for conducting a valid magnetometer survey, including towfish deployment, layback and sheave corrections, and diurnal variation correction using a base station.

Identify and interpret magnetic anomaly types (dipole, spike, dip, and linear features) and apply that knowledge to contact picking and contour map analysis.

Apply magnetometer survey results to real-world contexts including pre-dredge pipeline hazard assessment, RRC database cross-referencing, cultural resource surveys, and beneficial use site construction.

MODULE 1

Marine Magnetometer Surveying

• What a magnetometer measures, and how it detects disturbances in the Earth's magnetic field
• Nanotesla, gamma, and the IHO detection range formula
• Instrument types: proton precession, optically pumped, and fluxgate (e.g., Geometrics G-882, SeaSPY)
• Towfish deployment and passive system operation; layback correction and sheave offset as a measured value
• Diurnal variation and base station correction
• Anomaly signatures: dipole, spike, dip, and linear features; contact picking and contour map interpretation
• High-pass filtering, smoothing, and color ramp setting in MagPick-GT
• Applications: pipeline location and RRC database cross-referencing, pre-dredge hazard surveys, cultural resource surveys, and beneficial use site/construction surveys