About High Quality Clean Data

Using Magnetic Data to Develop Knowledge in Subsurface Investigations

Earth science data acquisition has become, in many instances, routine or considered to be routine. After all, we have been acquiring data for more than 50 years with increasingly sophisticated instruments. We have embraced the era of the digital computer and software, and thus, have become able to process and visualize much more data than ever before. Data volumes have increased significantly and with them our ability to perform much more advanced interpretation than ever before. Data have become our effective fountain of knowledge – data ultimately delivers knowledge as we seek to purse the answer to some undisclosed challenge in the subsurface.

High quality data from a ground magnetometer survey with a GEM Overhauser magnetometer and base station.

We have come to rely on ever increasing volumes of data to derive our knowledge-development and decision-making and therefore, we must never become complacent about the data we collect, manipulate, visualize and apply. This short article reviews the importance of data, the current state of magnetic data acquisition and the role and importance of instrumentation as we seek to acquire today’s most valuable resource in subsurface instigations – the data on which we grow our ideas and understand what is below the ground.

Importance of High Quality Data

In the digital age, data has become our lifeblood. It has highly leveraged value providing benefits of strategic, qualitative and quantitative benefit. These benefits motivate our vigilance to the instruments on which we base the importance of data in subsurface investigations.

Strategically, data has significant value as the lead input into the development of information and knowledge on which key decisions are based. All of our knowledge and decisions depend on data — surely this is one of the resources on which world trade depends in the 21st century. Data also has strategic value in a competitive sense as we protect our data assets behind firewalls and other digital fortresses.

Looking at the tangible benefit of high quality data, one can certainly look at subsurface mapping as a key qualitative means of knowledge development. Today’s mapping products are developed from raw original data, and serve to illustrate complex relationships at a glance. For the geologist, high quality magnetic data are key as results illustrate unknown geology as well as structural relationships. This is elemental data in subsurface data as illumination of geology is one of the key aims in earth science. Maps, as organizational tools, serve to develop information and knowledge through the underlying data which may be original or transformed through processing. Data for these applications may be acquired through a variety of platforms including ground, airborne and the newer, Unmanned Airborne Vehicle (UAV) platform.

In addition to mapping, data are also used quantitatively in a variety of advanced digital modeling algorithms. These algorithms have evolved in recent years and allow the more precise estimation of depth , body shape and attitude – three essential parameters in subsurface investigations. However, the qualtity of our modeling results will only reflect the quality of the data used to drive interpetations – again, we must stand on guard to ensure that we are acquiring the most high quality magnetic data possible.

With the increasing use of modeling software, the need for high quality data has never been greater. We refer to the old adage, “garbage in, garbage out,” to refer to modeling
studies that use less than ideal data.

Another example of modeling in which overall quality of data drives the successful interpretation.

Knowledge development, qualitative and quantitative results, and the integrity of subsurface investigations all depend on the quality of data input – next we look at the means being taken to ensure that only the highest quality data are acquired in the field.

Instrumentation Design – The Knife-Edge of High Quality Data Applications

Data from subsurface investigations are normally acquired through some sort of instrumentation on a ground, airborne, or UAV platform. And, as an instrument manufacturer, GEM ensures that its designs maximize data quality through three key aspects: minimal system noise, minimal shaping of signal, and optimal sensitivity matched to the specific particulars of a subsurface project.

Minimal system noise is a primary objective in design. Extensive experimentation, testing and fieldwork has shown that the company`s products deliver the cleanest signal possible in often demanding environments. An example of a specific design that minimizes noise is the Overhauser magnetometer – a magnetometer that GEM was the first to develop worldwide. On a technical level, this modified proton precession system uses radio-frequency energize to energize highly activated protons in a special fluid mix. Radio frequencies are outside of the wavelengths of proton signals – giving a noise-free means of energizing that differentiates it from a standard proton precession system. Noise-free signal contributes immeasurably to high quality data, and hence, final results.

Well-known cesium vapour magnetometers are an example where the signal is shaped by the electronics – resulting in additional noise in the measurements. This is a fundamental property of the physics of these systems. On the other hand, Potassium systems, such as the K-Mag (GSMP-35/25) and its airborne version, GSMP-35A/25A , do not shape the signal in any way. A characterstic of these latter systems is that they have a single, narrow peak, as opposed to a broad peak in cesium systems, which, in turn, allows for precise lock and frequency measurement – leading to higher inherent data quality.

A third element in deriving knowledge from data is the use of the optimal sensitivity to the subsurface problem at hand. Some basic applications, such as base stations and basic search functions, are supported well through the use of GEM`s Proton system (GSM-19T). The GSM-19T offers satisfactory data quality for these activities. On a higher level, is the higher resolving Overhauser (GSM-19) system which offers highly accurate data with about two orders-of-magnitude higher resolution than GEM’s Proton system – the optimal Proton unit available today. And for the most demanding applicatioins, the GSMP-35/25 and its airborne cousin, the GSMP-35A/25A, offer the ultra-high sensitivity that Potassium is known for as well as the clean signal that GEM`s design and manufacturing process ensures.

Matching Design to Application

In terms of their intrinsic quality of data, some systems are better suited to specific subsurface investigations than others. GEM`s Proton, Overhauser, and Potassium units represent a layered data acquisition regime which envelops many types of investigations. By offering the broadest range of acquisition platforms in the industry, the end user can ultimately design their program to the level of data quality required. This guides selection of systems and related spending – with the full recognition that premium data value represents a higher value offering from GEM.

In stationary applications, such as Magnetic Observatories and Volcanology applications, the data requirement is for results with high absolute accuracy – i.e. do not drift over time which can measure a year or more in duration. These constant, steady observations require the cool hand of the Overhauser line which offers the highest in absolute accuracy along with high resolution acquisition at pre-requisite sampling rates.

In ground applications, such as Mineral Exploration, Archaeology, and UXO, there are shifting requirements for data quality. In mineral prospecting, gold exploration represents a challenging application requiring the highest sensitivity for mapping of geology and structure. Hence, a high quality instrument such as the GSMP-35/25 is called for. Archaeology is driven by the twin needs of project budgets and resolution. Many archaeological features are subtle and much work has been performed with the Overhauser system which represents an attractive data acquisition platform (that can be automated) at an attractive price.

In airborne applications, such as helicopter and fixed wing work, there is an upswing in applications – all requiring ultra-high sensitivity especially since they are working from a moving platform above the surface of the earth where necessarily additional noise is introduced. This gives some advocacy for ground measurements as an alternative but clearly airborne measurements are here to stay, aided in some form, by ground follow-up. The overall requirement for resolution requires adoption of a system such as the Potassium system for airborne applications – this proven system delivers the highest in data quality and hence, knowledge content, of any system on the market.

The Unmanned Airborne Vehicle arena is another area where it is highly desirable to acquire high quality data for knowledge development. Here, application of the Potassium magnetometer or gradiometer (in the case of near surface investigations) lead to effective results that take advantage of the inherent design advantages of these systems. High quality results are assured with UAV platforms working for a variety of commercial, police or military applications.

Summary – From Data to Knowledge

In this digital era, our knowledge of the subsurface – key to making economic and other decisions – depends on the data we acquire and the instruments we employ in their acquisition. We must always stand on guard to protect the viability of our data through implementation of instruments that are designed for high quality data acquisition from the outset. GEM offerings, including the Proton, Overhauser, and Potassium magnetometers / gradiometers offer the broadest range of options for high quality acquisition – upholding GEM`s commitment to developing premium quality products that exactly meet the requirements of its users performing subsurface investigations.

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