See current research theme 'Algorithms & Software'

GPS Positioning for Helicopter Gravity Surveys

Mapping the spatial variation of the earth's gravity field is one of the most important techniques in exploration geophysics as it measures the distribution of different rock masses. Certain gravitational patterns may be indicative of surface or buried mineral ore bodies. Geophysical exploration companies therefore invest vast sums of money each year carrying out field surveys to map in detail the features of the surface gravity field across an area of interest.

GPS positioning techniques are now used for many surveying and precise navigation applications on land, at sea and in the air. For geophysical exploration applications all these positioning modes are used to 'geo-tag' the sites of geophysical measurements such as magnetism and gravity. Gravity surveys on land require that the height of the gravity station be determined to decimetre-level accuracy. Transporting of the gravity meter may be by vehicle or helicopter. Although carrier phase-based GPS techniques are the preferred positioning methodology, there is a serious constraint to present single-base receiver GPS systems under circumstances when the mobile user GPS receiver occupies a gravity station mark for just a few minutes: the separation between the two receivers (base and user) must be typically less than 15-20km. Such a constraint is particularly severe when using GPS in support of geophysical exploration across large land areas because of the significant costs associated with the frequent transportation of the base station receiver by helicopter to new sites in order that it always remains nearby to the gravity stations being surveyed.

 

The objectives of a ARC-SPIRT (Strategic Partnership with Industry - Research & Training) project "Development of a Medium Range, Carrier Phase-Based GPS Positioning System for Helicopter Gravity Surveys" (1999-2001) are to develop field procedures, a hardware package and a data processing software system for medium-range, sub-decimetre accuracy, rapid GPS positioning in support of helicopter gravity surveys, based on the use of a network of GPS reference receivers. The project Industry Partner was Normandy Exploration (NE), one of Australia's largest exploration companies, now part of Newman Mining.

This project took advantage of the multi-base station processing strategy mentioned in earlier projects, such as the Singapore multiple GPS reference station test facility. The then PhD student Michael Moore was initially engaged on this project and worked closely with NE to learn their current gravity survey methods and to test the proposed GPS positioning methodology. Liwen Dai and Horng-Yue Chen also made significant contributions to the algorithm development and testing.

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