Geophysical mapping is a key step in the process of remediating sites contaminated with unexploded ordnance (UXO). In order to accurately locate UXO, accurate measurements of the positions of the geophysical sensors are needed. The need for accurate, real-time pose (position and attitude) estimates has increased in recent years as more advanced sensors are developed that are capable of not only detecting anomalies, but also discriminating items of interest from cultural debris. The goal of this work was to improve the accuracy and availability of position measurements for geophysical surveys in heavy foliage environments by developing a Global Positioning System (GPS) software defined receiver (SDR) using vector tracking techniques combined with complementary sensors.
A GPS SDR has been developed that is capable of providing a position solution in degraded GPS environments such as under heavy foliage by making use of vector tracking techniques. The GPS position can be optionally blended with the output of a commercial inertial measurement unit to provide attitude measurements and allow brief periods of dead-reckoning during complete GPS outages. A chip scale atomic clock is also optionally used as a stable frequency reference to further improve the receiver’s ability to operate with a limited number of satellites. The SDR based design allows the receiver algorithms to be defined completely in software, allowing an easy upgrade path as more advanced algorithms are developed. This design also drastically reduces development cost when compared to a traditional application-specific integrated circuit.
A demonstration was performed at Redstone Arsenal in Huntsville, AL to analyze the performance of the system. The developed receiver was compared to a commercially available receiver typically used in geophysical surveys and the position availability and accuracy were compared. The demonstration showed significantly improved position availability and accuracy in dense foliage environments when compared to the commercial receiver. The developed receiver was comparable to the commercial receiver in open sky environments providing similar position availability with slightly reduced accuracy.
The primary issue to be considered when choosing to implement the demonstrated system is the presence of foliage or other GPS challenges on the site. Significant improvement in position availability and survey time were demonstrated for moderate to dense foliage. No significant improvement was seen in open sky environments.
Keyser, B., Hodo, D., Martin, S., Bevly, D., “Implementation Details of Real-Time SoC-Based Vector Tracking Receiver. Proceedings of the 27th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2014).
Martin, S.M. "Improved GPS Carrier Phase Tracking in Difficult Environments Using A Vector Tracking Approach." Presented to Southern California Chapter of the Institute of Navigation. Torrance, CA, December 2014.