Detection of UXO in Underwater Sites Using Towed-Array Resistivity/ Induced Polarization Measurements
MR-1325
Objective
Block Diagram of the Towed-Array Resistivity/IP System.
Detection and classification of unexploded ordnance (UXO) in a shallow underwater environment presents special problems that render some of the conventional geophysical methods normally used on land unusable or less effective. However, the deployment of galvanic resistivity methods is aided in such environments because the water provides a medium in which electrodes make continuous galvanic contact. The Model RX-1 Beach Mine Detector developed by the Office of Naval Research during the latter part of World War II represents an early effort to use the induced polarization (IP) method to detect mines. Though the RX-1 was deployed in Okinawa in 1945, the war ended before it was widely used and, as far as can be determined, there has been no further development of IP as a method for mine or other metal object detection. IP was, however, successfully developed and applied for mineral exploration.
The objective of this proof-of-principle project was to investigate the detection of UXO in underwater sites using a towed-array resistivity/IP system.
Technical Approach
On land, some experiments and tests have demonstrated that IP is associated with UXO. Resistivity and IP surveys also have been conducted in shallow water using a towed electrode array. In this project, IP responses associated with a few UXO types (e.g., grenade, mortar rounds, rockets, etc.) were measured in the laboratory, and a full-scale experiment was conducted using an instrument system previously assembled by Zonge Engineering & Research Organization, Inc. and deployed in shallow sub-bottom resistivity profiling for environmental applications. The effort sought to confirm that there is a measurable IP response associated with isolated metal objects that are either laying on the bottom in shallow water or buried immediately beneath the sub-bottom.
Results
Researchers conducted laboratory-scale model experiments and numerical model experiments in an effort to establish the scale of the IP response. The laboratory experiments and numerical modeling demonstrated that a measurable IP response is associated with metallic objects submerged in an aqueous electrolyte. Targets in a saltwater solution generate a significantly higher IP response than equivalent targets in fresh water. Based on results of the model, researchers designed a simple electrode array and tested the resulting system at the Mare Island Naval Shipyard (MINS) in San Francisco Bay. It is clear from the results that UXO generate a measurable IP response. However, targets seeded in the MINS Reference Area were not easily detected with the deployed surface electrode array partially due to inadequacies in the experimental apparatus. Small targets were not detected. As predicted, the MINS field test indicates that both target orientation and target/receiver dipole separation are significant detection factors.
Project Documents
Points of Contact
Principal Investigator
Mr. Scott Urquhart
Zonge Engineering, Inc.
Phone: 520-327-5501
Fax: 520-325-1588
Project Documents
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.