Geophysical Survey Capabilities In Wooded Sites With Robust Robotic Total Station Technology

Abstract

A significant need exists within the unexploded ordnance (UXO) community for improved navigation technologies for geophysical mapping, particularly in wooded and hilly sites. Present global positioning system (GPS) and acoustic technologies have limited application at many UXO sites. While some GPS methods exploiting multi-path rejection techniques achieve 1-meter accuracy in moderately wooded conditions, GPS is generally inadequate for UXO detection where vegetation obstructions are present. Acoustic methods are capable of mapping with sufficient accuracy for UXO detection in wooded sites, but are operationally complex and inefficient. Further, routine use under conditions of varying topography has not been demonstrated. Responding to these limitations, we have developed techniques for open and woodedarea geophysical mapping based on dual-laser robotic total station (RTS) technology. Our approach integrates geophysical sensors on a composite-material cart system with the Leica TSP1100 RTS. Custom software integrates data components. During operation, the robotic laser rangefinder is established over a benchmark and tracks a roving prism producing accurate 3D locations at 4 Hz. RTS technology has several advantages to conventional techniques including: 1) fast setup time ( cost approximately 50% of GPS; 4) survey range of 1400 feet and effective survey area over 140 acres under ideal conditions; 5) precision of /-5 mm (0.2 in) 2 ppm, or better than 0.25 inches at 1400 ft; and 6) elevation data as accurate as XY locations (the RTS has a circular error function). Since laser technology requires line-of-sight, location data is intermittent as the sensor system travels past trees. We addressed this problem by developing specific survey procedures that exploit prism tracking functions, and demonstrated that UXO surveys can be efficiently executed in hilly wooded areas producing data quality levels normally achieved during openareas surveys.