Airborne Geophysics on the Threshold of the 21st Century

“An intelligent system advances one step beyond chance only on the basis of information received.”
Norbet Wiener. A fundamental law of cybernetics.

Airborne geophysics has always differed from other geological investigation technologies in its exceptional speed, virtually unrestricted accessibility, cost-effectiveness, environmental compatibility, standardized methodology, relatively straightforward integration of methods, and exceptionally high statistical representativeness of data. For a long time, however, its shortcomings included low measurement accuracy and highly unsatisfactory accuracy in locating measurement points on the ground. Moreover, the range of airborne geophysical methods was largely limited to magnetic prospecting and gamma-ray spectrometry.

The development of airborne geophysics in the former USSR, like many other fields of science and technology, followed its own distinctive path. Whereas a purely pragmatic approach in the West led to narrow specialization and improvement primarily of equipment performance, our country also emphasized theoretical developments in general and targeted interpretation of the acquired data. It is no secret that many ideas proposed by our scientists and specialists found their technical implementation abroad.

It is well known that airborne geophysics led to the discovery of exceptional uranium, iron, diamond, gold, and other mineral deposits in the former USSR, Australia, Canada, Africa, China, the USA, and other countries during a period of relatively modest technical development. Yet in the 1980s, when its technical level became extraordinarily high (multichannel large-volume scintillation gamma-ray spectrometry, proton and quantum magnetometers, diverse electromagnetic equipment, digital recording systems, etc.), its exploration successes began to decline.

This was because, after large exploration targets with strong diagnostic contrasts in simple geological and geophysical settings had been discovered, airborne geophysics turned to low-contrast targets in complex natural environments. Under these conditions, simply identifying geophysical anomalies closely resembling background environmental variations in several parameters became ineffective. An exploration scheme oriented solely towards detecting anomalies from the ultimate exploration targets—the so-called “shortened” scheme—no longer produced the desired positive geological results.

An obvious response was to improve measurement accuracy and integrate different methods on a single aircraft. Alongside this approach, however, Russian practice, particularly at GNPP Aerogeofizika, also developed a transition to a so-called “staged” work scheme and the use of targeted airborne geophysical technologies for geological investigation. This approach involved identifying a natural hierarchical series of intermediate exploration targets and corresponding work phases or stages, defining specific prerequisites and indicators for each, and zoning areas according to landscape and geological exploration conditions and the reliability of completed prospecting. GNPP Aerogeofizika demonstrated the effectiveness of this approach as early as the 1970s–1980s in exploration for diamonds, gold, bauxite, and other minerals.

The range of remote-sensing methods has now expanded sharply, primarily through the addition of various airborne electromagnetic configurations, multicomponent magnetometry, airborne gravity prospecting, and thermal infrared imaging. Modern equipment for many remote investigations has already crossed the accuracy threshold separating airborne geophysical surveys from ground surveys; in magnetometry and gamma-ray spectrometry, measurement accuracy and survey quality have already surpassed the corresponding performance of ground surveys.

Recent years have seen a fundamental qualitative improvement in the georeferencing accuracy of airborne geophysical measurements. Modern satellite navigation systems determine instantaneous coordinates with an accuracy of 10 m or better, and, when required, down to a few metres.

Airborne geophysics can now be regarded as a fundamentally new technology for investigating the Earth's surface and subsurface. Moreover, because the cost per line kilometre of the most common, widely used airborne geophysical surveys is an order of magnitude lower than that of their ground equivalents, airborne geophysical technologies are preferable for most geological investigation tasks (geological mapping, mineral exploration, environmental monitoring, and many others) in terms of economics, quality, and reliability of results.

Today, airborne geophysics is among the most rapidly expanding technologies worldwide. It has achieved impressive successes in North and South America and Africa. Even small European states (Austria, Finland, Czechia, and others) increasingly emphasize conducting airborne geophysical surveys with their own resources, despite extremely detailed geological coverage of their territories by ground methods. In 1997 alone, the Australian government allocated more than 10 million dollars to private companies to modernize existing and develop new airborne geophysical systems. The total global market for airborne geophysical services amounted to approximately 250 million dollars in 1996.

Since their inception, airborne geophysical technologies have always been relevant to Russia, with its vast expanses, enormous distances, and underdeveloped infrastructure. The present economic situation in the Russian Federation has several additional characteristics, determined on the one hand by the specific economics and management of the geological sector and mining industry in the former USSR, and on the other by the particular mechanisms chosen for the sector's transition to a market economy and the initial outcomes of that transition.

Without discussing the evident importance of mining and the fuel and energy sectors to our country, or the equally evident need for large-scale investment in these sectors of the Russian economy, we note that specific, highly reliable information is extremely important to executive authorities and potential investors on the principal factors determining appropriate investment directions and their effectiveness. Government bodies need this information to assess the overall condition of different branches of the mineral resources industry and develop an appropriate investment-attraction programme. Private investors also need it to select the most effective (profitable) investment direction.

However, the country's current transition to a market economy has sharply altered the commercial value of various categories of resources and reserves, both previously included and excluded from the official balance. The high costs of current or planned extraction under market conditions have removed substantial portions of various raw-material types from the state balance of reserves and resources.

The gap between mineral reserves actually confirmed in the subsurface and prognostic resources existing as scientific (working) hypotheses has widened dramatically. The gap between prognostic resource estimates in categories Р3 and Р1 is especially dangerous: the former are general theoretical assumptions about the potential localization of resources over large areas (such assumptions have always been numerous), whereas the latter already represent actual small areas and anomaly-producing objects localized in the subsurface that can be further investigated and evaluated (unfortunately, such objects are few).

These conditions clearly require prompt action. An accelerated inventory of prognostic resources is needed in new districts and around operating mining enterprises: all hypotheses and assumptions must quickly be reduced to specific ore-prospective structures, areas, and anomalies localized in the subsurface, suitable for actual evaluation rather than discussion. This work should produce geological and economic information packages for specific minerals and regions.

The national economy needs sufficiently reliable data on the actual structure of commercially valuable prognostic resources of different minerals; effective public administration requires urgent optimization of the relationship between resources and reserves and, within the latter, prognostic resources of different categories. Government bodies urgently need packages of highly reliable geological and economic information to attract investment into the geological sectors most important to the country. Naturally, domestic and foreign investors also require these data. Such information must be transparent—that is, comprehensible and verifiable in every element—and have a narrowly targeted commercial focus. It should therefore include a block of necessary, metrically reliable factual data, a block of general and targeted interpretation, and a block assessing the reliability of results, in the formats most widely used today (for example, GIS).

Such packages are needed for areas with operating enterprises as outcomes of inventory or reassessment work, and for new areas where prognostic resources are likely to be localized, improving their relationship to reserves in the national mineral resources balance.

The characteristics of current developments in airborne geophysics, together with the condition of the geological sector in our country noted above, allow targeted airborne geophysical technologies for geological investigation to be regarded as a principal instrument for restoring and developing the national mineral resource base for many, if not most, minerals. AIRBORNE GEOPHYSICS itself—a technology essentially converted for geological use—thus also becomes an attractive target for effective investment.

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For more than 25 years, the Federal State Unitary Research and Production Enterprise Aerogeofizika has followed a distinctive path in developing airborne geophysical technologies. As early as the beginning of the 1970s, this involved introducing the most promising foreign equipment developments into domestic airborne geophysical practice. It developed its own series of airborne gamma-ray spectrometers and magnetometers, its own version of airborne electromagnetic equipment, and an instrumentation and computing system for thermal infrared imaging. This also includes unique data-processing and interpretation technologies. Its most important achievement was the development of airborne geophysical exploration technologies that brought the country new mineral deposits, including exceptional ones.

Despite the current difficulties of economic transition, GNPP Aerogeofizika has preserved its team of highly qualified professionals assembled over many years and modernized its equipment using its own profits.

Today, with 75 employees, GNPP Aerogeofizika can conduct simultaneous operations with five unique systems incorporating fixed-wing and helicopter electromagnetic systems, high-accuracy caesium magnetometers, and high-resolution multichannel gamma-ray spectrometers, and can perform airborne thermal infrared, aerosol, and gas surveys. GNPP Aerogeofizika has state-of-the-art navigation equipment, variation stations, and computing systems for data processing, interpretation, and presentation.

In our view, however, the most important point is that, unlike foreign practice, we are already able to offer the airborne geophysical services market targeted geological investigation technologies that not only acquire high-quality primary information but also provide in-depth interpretation of its meaning.

We hope that this approach will produce further positive results and, in time, become widespread both in our country and worldwide.