Determination of Vehicle Acceleration by Using the GPS Phase Acceleration
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Date
1997-04
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Ohio State University. Division of Geodetic Science
Abstract
Airborne Gravimetry (AG) using a system integrated with INS/GPS is an efficient and relatively economic and effective technique to collect gravity data. This technique is covering the gap in resolution between conventional terrestrial methods and satellite based methods. While static terrestrial methods provide the gravity measurements with about 0.02 mgals of accuracy over 1 km resolution or higher, satellite based methods could give a resolution of 50-100 km with several mgals of precision. The Global Positioning System in its interferometric mode has proved to yield geodetic positions with about 1-2 cm of precision for up to 10 km baselines. Airborne Gravimetry exploits the high accuracy geodetic positioning given by the GPS system to correct the gravimeter measurements by obtaining the aircraft vertical acceleration. With this method, the gravity signal can be obtained with 1-6 milligals of accuracy over 2-5 km resolution. The present study focuses on the direct use of the GPS phase acceleration to compute the acceleration of the aircraft. The GPS phase acceleration has the advantage of being immune to the cycle slip occurrence; full-cycle ambiguities are not determined. An algorithm was developed and tests were made using two different GPS data sets. Numerical tests showed that not only Selective Availability, but the receiver clock error is a major source of error for the GPS phase acceleration. Therefore, double differences were performed to cancel or drastically reduce common errors related to satellites and receivers. The time differentiation of the GPS phase was accomplished with a fifth-order B-spline with smoothing over different number of epochs, between 10 and 100 one second epochs. The use of the GPS phase acceleration to compute the platform acceleration gives a precision of the level of a milligal for smoothing intervals of less than 100 s. The three components of the acceleration vector are determined. Therefore, this approach to GPS derived acceleration could be applied to vector gravimetry as well.