Airborne Geophysics – Evolution and Revolution

The past decade (1997-2007) of airborne geophysics has been an exciting time. Mineral exploration activity and expenditures have been cyclical, but the decade has ended in what can only be referred to as “boom times”. The airborne survey industry itself has undergone dramatic changes, moving into a period of consolidation during 1999/2001, only to be followed by a period of expansion with new companies being formed and prospering. At the present time there are more independent commercial airborne survey companies operating than before the consolidation. The client base has also been altered significantly. The trend to “buying reserves” instead of “finding them” has resulted in a series of mergers and acquisitions amongst the major mining companies. Fortunately the buoyant financial markets and recent strong commodity prices have allowed the “juniors” to take up the slack and in many cases finance exploration joint ventures with the majors. A cloud on the horizon is the aging and declining pool of experienced people in the industry. Against this background of market dynamics some airborne geophysical methods such as radiometrics and magnetics have experienced incremental, basically evolutionary developments over the decade. One exception to this is the trend towards low level high resolution magnetic surveys employing helicopters and “crop duster” aircraft. Another would be the introduction of UAV’s for magnetic surveys although the importance of this survey technology remains to be proven. Much more dramatic developments, or a revolution, have occurred in gravity and electromagnetics. In gravity there have been significant new developments in the measurement of basic airborne gravity. However, the most significant development for mining applications has been the introduction of airborne systems to measure gravity gradients, termed airborne gravity gradiometers (AGG). Airborne electromagnetic developments present a bit of a paradox. In both helicopter and fixed wing frequency domain systems developments have been incremental and primarily focused on new applications. The true revolution has occurred in the development and application of helicopter time domain (HTEM) systems and to a lesser degree in fixed wing time domain (FTEM) systems. The last five years of the decade have seen HTEM move from the development stage to capturing a significant portion of the world wide airborne EM survey market. Other FTEM and HTEM developments have included a push to greater bandwidth as evidenced by the introduction of B-field and step response data, the use of square wave transmitters,, new airborne platforms with higher performance capability and improved interpretation techniques.Other related airborne geophysical system developments have included hyperspectral imaging and a revisiting of the natural field airborne EM method, AFMAG.There remain enough opportunities (and unresolved issues) to create the opportunity for significant new advances over the next decade.