The conductivity of water, which is controlled by the concentration of dissolved ions, shows how well the water conducts electricity. Airborne electromagnetic geophysical surveys are used to collect resistivity data. The interpreted data provide information on geologic and hydrologic conditions including locations of geologic boundaries and spatial changes in water quality, which are of use to ground-water modelers. Interpretation relies heavily upon the use of borehole geophysical logs, namely induction logs from monitoring wells and water quality data. Surface geophysical measurements are used to refine the interpretation.
Electrical current flowing in transmitter coils in the bird induces current in the ground.
The intensity of the induced currents increases as the ground conductivity increases. The magnetic fields generated by the induced currents are recorded by receiver coils in the bird. The transmitter coils are excited at five frequencies to obtain different depths on investigation. Flying with the bird 30 m above the ground, measurements are made every 0.2 second along flight lines. Flight lines are nominally spaced 400 m apart.