Laboratory and field evaluation of Precise Lightweight GPS Receiver (PLGR+95 and PLGR+96) accuracy

The Geospatial Information Division (GID) within the U.S. Army Topographic Engineering Center (TEC) has used Global Positioning System (GPS) equipment to support Army studies since 1988. The Precise Lightweight GPS Receiver (PLGR) in the real-time absolute mode has been a critical component in successfully completing many of these evaluations, especially those requiring the collection of ground truth data. Typical Precise Positioning Service (PPS) PLGR accuracies of 10 to 15 meters (horizontal) had been more than adequate to meet earlier study requirements. However, other projects using high-resolution (<5 meters) data sources have focused more attention on PLGR accuracy and the need to better understand potential PLGR capabilities in the field. This paper describes testing and evaluation of PLGR+95 and PLGR+96 equipment. The PLGR+95 was used during three field projects that took place between June 1995 and July 1996. In each case, TEC scientists collected coincident positions from both PLGR and a higher accuracy control mechanism such as differential GPS or a total station tied to first-order survey control points. Over 1000 positions were included in the subsequent statistical analysis which determined the average "accuracy" of the PLGR versus control under actual field conditions. The later generation (PLGR+96) equipment was tested in-house (at the U.S. Army Topographic Engineering Center) and in the field (at Fort A.P. Hill, Virginia) during July 1997 and July 1999 respectively. The in-house testing was performed in open sky conditions while the field evaluation was conducted in a forested environment. Performance of the PLGR+96 Wide Area GPS Enhancement (WAGE) capability, "position averaging", and signal acquisition and accuracy under a vegetative canopy are discussed.