GPS Accuracy and Reliability Assessment - The Truth in the Truth Source

Making sausage, writing legislation, and determination of performance metrics are activities most people would prefer to be kept out of sight. But the Atlantic Test Range (ATR) at the U.S. Navy, Patuxent River Air Station (PAX) has a need for an ongoing, transparent assessment of the reliability and accuracy of its GPS system. While sausage and legislation may remain mysterious, this paper describes a rigorous, documented method used on a repeated basis to establish performance metrics using the best, rigorous methods of measurement science. The GPS group at ATR is charged with providing GPS data for a variety of vehicle test applications. In addition, and with the greatest challenge, it also provides the baseline calibration system for radar, theodolyte, IR, and laser tracking and ranging systems. While each of these tracking instruments has its own calibration method, GPS/INS technology provides an innovative method to verify accuracy under realistic, operational scenarios. All of these applications require performance metrics to make critical test plan design decisions and test performance evaluation. Consequently, the GPS team at ATR has established the GPS Accuracy and Reliability Assessment (GARA) project to develop these statistics and make them generally available and understandable. Prior to this program we have relied on vendor specifications which tend to be too optimistic for the realworld applications we address. Some of the main objectives for GARA are: • Establish performance metrics that are specific to the ATR range including its reference receiver network, specific GPS receivers, and that reflect ATR’s best engineering and operations practices. • Develop an accuracy and reliability assessment process that is repeatable, automated, rigorous, and as transparent as possible. • Ensure the results are published broadly and easily available throughout ATR and its customer base.