Improved GPS Accuracy for TSPI Obtained Through Post-Flight Analysis

Carl E. Hoefener, Gerald S. Dankner

Abstract:	Improved GPS accuracy for TSPI can be obtained through Post-Flight Analysis. When instrumenting a test vehicle to obtain TSPI data for test and evaluation many options are available. If GPS is to be utilized, two implementations can be considered. These are either fly a GPS receiver on the test vehicle, determine TSPI in the vehicle, then telemeter the data to the ground; or fly a GPS frequency translator in the vehicle, transmit the broadband GPS data to the ground, and perform the TSPI at the ground station. This paper shows that significant accuracy improvement can be obtained by utilizing a GPS translator in the test vehicle in preference to an onboard receiver. These accuracy improvements are obtained for two significant reasons. An onboard receiver processes only ranges from four satellites to obtain its position. The four Satellites selected may or may not provide the optimum GDOP at that particular location. In the case of a GPS translator based system, data from all satellites in view are transmitted to the ground for processing. The broadband data from all the satellites are recorded for post-flight analysis. When performing post-flight analysis, satellite selection can be optimized to select the best GDOP or process data from all satellites in view that will provide maximum accuracy. The ability to record the broad band data also allows other significant post-flight advantages. Prior to a flight test, the flight dynamics of the test vehicle can only be estimated. The parameters of the tracking filters in the onboard receivers are set accordingly. If the target experiences unexpected dynamics, which is possible during a test flight, the receiver may fail to lock up on the satellites, and all TSPI data will be lost. In case of the GPS translator-based system, all the satellite data will be recorded at the ground station. When this data is played back for post-flight analysis, the filters may be optimized for the actual flight dynamics experienced, and the TSPI data will not be lost. In addition data processing may be used to fill in data gaps.
Published in:	Proceedings of the 1987 National Technical Meeting of The Institute of Navigation January 20 - 23, 1987 Anaheim, CA
Pages:	159 - 160
Cite this article:	Hoefener, Carl E., Dankner, Gerald S., "Improved GPS Accuracy for TSPI Obtained Through Post-Flight Analysis," Proceedings of the 1987 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1987, pp. 159-160.
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