Department of Defense ranges and installations have munitions and explosives of concern (MEC) in underwater environments, posing hazards. Over 10 million acres potentially contain underwater MEC across 400 sites. The U.S. Navy and Marine Corps have identified an additional 20 sites. The goal of this project was to demonstrate a marine-towed system ("UltraTEMA-4") for detecting and classifying buried ordnance. This was achieved through a number of shakedown tests in Washington State as well as a demonstration at the Sequim Bay test site in 2022.

The UltraTEMA-4 integrates Gap Explosive Ordnance Detection's multi-sensor UltraTEM^® Marine package into Tetra Tech’s towed electromagnetic array platform. Components of the system, are as follows:

• UltraTEM Hardware: A multi-sensor system using electromagnetic induction to detect buried metal that has previously been extensively used in Europe for marine surveys.
• TEMA Hardware: Towed Electromagnetic Array (TEMA) system has been refined over two decades. The TEMA-MK4 scales up previous designs to achieve a 4m wide swath with improved flight control, attitude, and altitude maintenance capabilities. 
• Data Processing: Data is processed by Black Tusk Geophysics using unexploded ordnance (UXO)Lab software which is optimized for UXO detection and classification.

The system's demonstration involves blind-tests, using known and unknown items placed in Sequim Bay. Previous tests in 2021 evaluated the UltraTEMA-4 system’s capability, especially in terms of stability, altitude control, and line following. Two areas in Sequim Bay were selected for performance evaluation: a calibration area and a blind test area. Different modes of data collection were evaluated, focusing on detection and classification.

The 2022 Sequim Bay demonstration achieved its performance objectives. Specifically:

• UltraTEMA-4 can accurately track the sea-bottom profile.
• Correct classification of 100% of the seeded targets of interest when the system was flown close to the sea-bottom (< 1 m elevation).
• Data analysis showed high precision in various metrics, including a root-mean-square positional accuracy of 20 cm.

In particular this project demonstrated that Advanced Geophysical Classification is feasible in the marine environment as long as the system is kept close to the sea-bottom.

The Sequim Bay site is ideal for deploying the UltraTEMA 4 tow-platform due to its optimal water depth, ample maneuvering space, and protection from winds and swell. Future tests should showcase UltraTEM Marine technology in varied conditions, including shallow waters and offshore environments affected by swells.