Computation of datum shift parameters between two navigation datasets
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ORIGINAL PAPER
Computation of datum shift parameters between two navigation datasets Khalid Amin Khan 1 & Gulraiz Akhter 2
Received: 18 February 2015 / Accepted: 7 December 2015 / Published online: 10 March 2016 # Saudi Society for Geosciences 2016
Abstract Geophysical surveys require precise navigation data which is usually acquired through real-time kinematic GPS. The acquired data needs to be transformed from the GPS reference datum to the local datum, by computing datum shift parameters using control points in the survey area. Oil and gas industry archives contain data from seismic surveys, conducted over the years by various data acquisition crews using different datum shift parameters. Sometimes these parameters are not documented in the navigation data headers. This leads to geo-referencing problems when combining data from different surveys. This paper reviews the transformation models and presents a simple approach for computing Molodensky-based datum shift parameters, by identifying common points between two surveys on a map. A real example is included to show the successful implementation of this method. Keywords Datum shift . Molodensky transformation model . Navigation data . Geophysical exploration
Introduction During the last two decades GPS is being used for navigation in geophysical surveys, particularly seismic operations carried out by oil and gas industry. The World Geodetic System 1984
* Khalid Amin Khan [email protected] 1
K-Tron Research Inc., 347-A Westridge I, Rawalpindi, Pakistan
2
Department of Earth Sciences, Quaid-i-Azam University, Islamabad, Pakistan
(WGS-84) is the reference system of GPS coordinates (Lohmar 1988). The seismic and well coordinates recorded in the earlier geodetic systems need to be converted to WGS-84 datum. Thomas (2004) has discussed how difficult, time-consuming, and expensive is the conversion process. The coordinate transformations between the WGS-84 datum and the local terrestrial survey datum require seven parameters consisting of three translations, three rotations, and one scale factor (Featherstone and Vanicek 1999). The most widely used datum shift transformation models are Bursa-Wolf (Bursa 1962; Wolf 1963) and Molodensky-Badekas (Molodensky et al. 1962; Badekas 1969) because of their ease in application and resulting accuracy. The Molodensky transformation is widely implemented in many geodetic programs and as such is the most required transformation model (Newsome and Harvey 2003). Often, it is simply expressed by the three translation parameters as provided in Defense Mapping Agency (1991) publications. Thus, the threeparameter version of Molodensky transformation model is more commonly used in geophysical exploration (Rayson 1998). Seismic operations carried out by oil and gas industry over the years have resulted into several vintages of seismic data, each using a different set of datum shift parameters. It is highly recommended that while storing the navigation data, the datum shift parameters must be documented in the header of industry
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