Meeting Tighter Navigation and Data Qc Requirements for Mec Investigations

Abstract

Currently, good DGM implementation for MEC can get 1 to 2-ft radii navigational accuracies during production and better during demonstration surveys. The differences between a 1-ft and a 2-ft implementation are the selection of appropriate navigation systems, up-front thought in survey design, and rigorous QC including inspections, audits, and failure analysis. At two sites at the former Seneca Army Depot, where the performance objective was to detect small (down to 20mm) target items, Shaw Environmental (Shaw) used an EM-61MK2 towed array with robotic total station navigation that reliably got close to 1-ft total positional error site-wide. Keys to the implementation included optimization of the form factor (deployment system and geometry) to minimize bounce, pitch, roll, and yaw, software and logger selections to minimize latency issues, and establishment of many QC control points. The volume of DGM production data, QC data, QC assessments, and documentation can be overwhelming. Although fixed calibration site data were good indicators of field data quality, the most time efficient indicators of positional data quality were known location QC points. The operational demands of navigation, logging, and monitoring multiple simultaneous data streams on the equipment operators are a challenge. Audits and failure analysis are performed to ensure compliance with operating procedures and, equally important, to optimize those procedures to minimize the potential for incidental or catastrophic errors. Navigational Accuracy and Precision U.S. Army Corps of Engineers (USACE) quality control (QC) standards and data quality objectives (DQOs) typically govern digital geophysical mapping (DGM) requirements for munitions and explosives of concern (MEC) investigations (USACE, 2003, 2004). The general requirements for horizontal positional accuracy for DGM, which apply essentially regardless of target munition size or terrain or cultural conditions, are: Table 1.: General Positional Accuracy Standards Metric Evaluates Repeatable positional accuracy of +/20 cm on standard QC tests 1) Have an acceptably accurate and precise navigation system 2) Have a QC program to continuously assess navigational data quality 95% of all reacquired anomaly locations must lie within a one meter radius of their target pick location 1) Operator implementation of equipment 2) Appropriateness of survey design 3) Sum of all navigation errors in data collection, processing, and target selection 95% of all excavated items must lie within a 35 cm radius of their reacquired surface location 1) Relocation used to refine target location 2) Relocation operator implementation