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Earth Explorer is an online source of news, expertise and applied knowledge for resource explorers and earth scientists. Sponsored by Geosoft.


News & Views

News Archive

February 9, 2016

Rio Tinto scales up its big data ambitions

Rio Tinto is opening its "vast troves" of exploration data to junior explorers in the hopes they will help sift for opportunities and supply ideas and labour...

February 8, 2016

Online portal improves access to geoscience data from Africa

The Botswana Geoscience Institute is launching a Geoscience Portal...

February 8, 2016

5 Best Minerals & Fossils To Buy With Your IRS Tax Refund

You just got your IRS tax refund and now you're presented with some cash to go out and buy one of a kind minerals and fossils from your local...

February 5, 2016

World's largest offshore windfarm to be built off Yorkshire coast

Dong Energy makes final investment decision on 1.2-gigawatt project that will power more than a million UK homes...

February 2, 2016

World's top 10 rookie gold mines

These high-grade mines will soon start competing with gold mining's industry leaders ...

January 25, 2016

Exxon Mobil Corp's defiant outlook predicts Canadian and Venezuelan oilsands output will 'quadruple' over next 24 years

In sharp contrast to the grim medium-term prognosis for the Canadian oilsands, Exxon Mobil Corp. is predicting sunnier times for bitumen in the decades ahead...

January 23, 2016

Magnetic Survey Keeps Cost Down

At a contaminated furniture factory site in North Carolina, a reconnaissance magnetic survey was conducted toward the end of a Phase 2 investigation ...

December 18, 2015

Geology Students Are The Happiest On College Campus Study Finds

Geology students are the happiest with their degrees according to the National Student Survey...

November 10, 2015

AGU's First Ask Me Anything: Water Science and Management

AGU's first ever Reddit Ask Me Anything, features Dr. Alberto Montanari, editor in chief of Water Resources Research on 12 November, from 12:00-2:00 P.M. EST, via Reddit's r/science portal ...

November 5, 2015

Massive graphite discovery could be on the cards for NQ

Graphite is a mineral of immense potential and value - its purer forms sought out for use in mobile phone technologies and the batteries that power...

November 1, 2015

Australia's junior sector turns to crowdfunding

Australian junior miners have decided to battle the capital drought afflicting the sector by turning to the Internet to raise funds...

October 28, 2015

Saudi Arabia's mining sector to triple by 2030

Mining contribution to GDP to reach SR260 billion by 2030 and create more than 100,000 jobs for citizens ...

October 26, 2015

Grant enables pioneering research of vast river systems in Great Plains and Asia

It's hard to exaggerate the importance of rivers to sustaining life for animals and people...

October 16, 2015

INFOGRAPHIC: "Gold off to races?"

This week, gold made a significant technical breakthrough ...

October 15, 2015

BHP raising $6.5bn fresh sign of mining turnaround

The mining industry's big players are themselves slowly beginning to change tack...

October 7, 2015

Could rock formations along Alabama highways offer clues to climate change?

Making predictions about climate variability often means looking to the past to find trends...

October 2, 2015

Petrobras' pre-salt drilling confirms high quality oil potential in Carcará

The drilling of the third well in the Carcará area (Block BM-S-8) in the Santos Basin's ultra-deep waters...

October 1, 2015

Eni enters Mexico with the development of three oil fields offshore

Eni won with a 100% share a production sharing contract to appraise, develop and exploit the oil fields...

Harnessing the Power of Parker

April 29, 2010

Even with the dramatic advances in computation speed, the demands of the petroleum exploration industry to find more oil faster has grown exponentially. Geosoft’s Gerry Connard explains the advantages of using Fast Fourier Transforms (FFT) for gravity and magnetic modelling.

What research is the approach based on?

Robert Parker’s seminal paper published in 1972, The Rapid Calculation of Potential Anomalies, has led to a revolution in using FFT for gravity and magnetic modeling using ‘gridded’ data. Since then, a number of additional papers, including some by Parker himself, have extended and improved Parker’s original work. Richard Blakely’s 1995 book summarizes most of this development and provides some additional, related FFT algorithms for FFT-based gravity and magnetic calculations (such as Blakely’s ‘Earth Filters’).

What are the advantages of the FFT-based methods?

Parker describes in the introduction of his 1972 paper that the computation time for a model grid containing N points is proportional to N ln(N). For equivalent space-domain calculations on the same type of model, the computation time is proportional to N2. This difference is not so significant for small models. For example, to calculate the response of a grid with 100 points, the space-domain approach would require approximately 20 times as many calculations as the FFT approach. However, as the number of grid point increase, the ratio of the number of calculations in the space-domain approach compared to the number of calculations in the FFT-based approach increases rapidly. For a grid with 1000 points, the ratio is 144. For a grid with one million points, the ratio is 72,382. So if the FFT-based approach took one minute of compute time, the space-domain approach would take 50 days.

Are there disadvantages of the Parker method?

There are pitfalls in the FFT-based calculation approach, including but not limited to the problems of edge effects, periodicity, and the fact that the original Parker algorithm is based on the convergence of a Taylor-series approximation. With two decades of practical experience using the FFT-based approach, most of these problems have been solved or at least minimised. For example the “Earth Filter” algorithm does not need the Taylor-series approximation.

What are your future predictions?

The FFT approach continues to evolve. Two papers by Parker in 1995 and 1996 extend his method to compute the results on an uneven surface. This allows more flexible models that more closely resemble a real earth model which are more appropriate in many exploration scenarios. In 2009, a new paper published by Caratori Tontini and others describes how to use 3D FFTs for gravity and magnetic calculations that will likely lead to significant improvements in FFT-based methods. Although raw computing power continues to grow according to Moore’s Law, our computing needs are growing even faster. Explorers today are taking advantage of a wealth of detailed exploration data to build larger and more complex models with grid sizes often exceeding one million points. FFT-based methods will play an important role in tools for the utilization of gravity and magnetic data in large, detailed models.

In spite of the disadvantages of the computational speed of space-domain techniques, they will also continue to be important tools in the interpretation tool kit. Space-domain techniques are inherently more flexible than FFT-based techniques and more easily utilised for inversion schemes. One powerful approach is to use a hybrid technique that combines both FFT-based and space-domain techniques in a modeling tool. Cloud computing (such as using large banks of parallel processors at a remote site) is also likely to be part of our exploration computing future. This approach is already being used by companies like Microsoft and Google to bring amazing computing power to desktops around the world.

Gerry Connard is the Petroleum Industry Market Manager with Geosoft. Connard is a geophysicist with over 30 years’ experience in the exploration industry. He founded NGA, Inc. and developed gravity and magnetic profiling and modelling software – GM-SYS and GM-SYS 3D.