The pattern of a magnetic anomaly varies with the dip of the inducing field For an aeromagnetic survey intrndetl

to discover induced dipole sources, the best flight direction is defined as the one offered maximum target \\‘itlth by an anomaly. This direction may depend on the amplitude of the anomaly. h method is prolwsed for estimatingrftciency of direction for a range of anomaly amplitudes. The efficiencies of lines bearing north, northeast, and east are comparetl. At the equator, lines bearing north are twice as efficient as lines bearing east. \Vith increasing inclination, the advantage of lines bearing north tlisappears at dips of about 20 decrees. Lines bearing northeast are chosen for clips hetneen 20 and 70 degrees. ITlight direction is unimportant for clips greater than 70 degrees.