The objective of this project was to leverage the Office of Naval Research’s (ONR) Mine Countermeasures (MCM) unmanned underwater vehicle (UUV) assets to evaluate and demonstrate the applicability of existing ONR MCM UUV technologies integrated with advanced sensor packages for facilitating detection, assessment, and characterization of underwater munitions.
The two UUVs were selected from the National Unmanned Systems Shared Resource Center (NUSSRC) inventory to address the detection and characterization of underwater munitions, the Remote Environmental Measuring UnitS 100 (REMUS 100), and the Bluefin-12 Buried Mine Identification (BMI) system. Additionally, the data collection for this experiment occurred during and was leveraged off of a 2011 ONR demonstration. The ONR demonstration produced an opportunity for the demonstration of a third system, referred to as the REMUS 600 BMI UUV, which contains a suite of sensors including a magnetic sensor, a Laser Scalar Gradiometer (LSG).
A number of sensors were employed in the demonstration. The BMI sensor suite consists of the Buried Object Scanning Sonar (BOSS) and the Realtime Tracking Gradiometer (RTG) fitted to the Bluefin-12 UUV. The REMUS100 system carries a dual frequency, 900/1800 kHz side scan sonar. The REMUS system provided high resolution acoustic images of proud objects, while the BMI sensor suite on the Bluefin-12 UUV provided acoustic images of buried objects and the magnetic moments of targets or clusters within range of the RTG sensor. The combination of the data from both UUV systems was designed to enable detection of acoustically reflective targets and discrimination between proud and buried state, provide size and aspect information, and indicate which contain magnetic material of the level seen for munitions.
A small underwater munitions test site was planted in the Davis Point area of St. Andrew Bay near Naval Surface Warfare Center-Panama City Division (NSWC PCD). Five nominal 100-m-long target lines spaced 2 m apart were laid parallel to each other. The first two lines had individual targets spaced along the lines and aligned at random orientations relative to the target lines. One line had the targets proud and the other line had the targets flush buried. The third through fifth lines had two clusters of targets on each line. Lines one and two provided baseline measurement data for each individual target type. Lines three through five provided acoustic and magnetic data for clusters of munitions in different states of burial and orientation. The planted locations of the targets were determined by their drop locations from the surface vessel using plumb lines and a GPS system.
The BOSS sensor clearly demonstrated the capability of detecting and imaging unexploded ordnance (UXO) targets of the class M targets in proud, partially buried, and fully buried configurations. Discriminating between the different targets was accomplished by comparing the known target physical dimensions with the measured dimensions extracted from the BOSS imagery. However, discriminating multiple targets in a clustered configuration was difficult for the case of targets closely spaced together (target 16-CL1-M). This is due to the medium resolution of the BOSS sensor. In previous years, the developer of the BOSS system has recommended increasing the transmit frequency to increase the resolution to enhance the imagery but funding for this effort has not been forthcoming.
The RTG experienced hardware failure during the data collection event at the end of June, leading to lost data. A likely candidate for this failure is the oil-filled cables that connect the sensor head to the electronics bottle. These cables and their connection points have failed in the past with similar effects on the data. A refurbishment and recalibration of the RTG system would be beneficial for future testing events and will be necessary to improve results.
The technologies encountered numerous problems during their deployment, including the failure of multiple channels in each sensor, not allowing much of the data to be recovered. The sensor suite used in the experiment was unique research and development equipment developed by the Navy for finding buried mines. As such, it cannot be procured commercially. Additional equipment would have to be custom-built.
Improvements in magnetic sensors have been made since the RTG sensor was constructed, and alternate sensor designs might be considered, including the LSG sensor. Collaboration between government and contractor subject matter experts would be required to develop a state-of-the-art gradiometer suitable for integration with the Bluefin-12 UUV and the BOSS sensor for regular use in munitions surveying. As a part of that effort, software for processing gradiometer and BOSS data would be streamlined to enable survey contractors to use the system with minimal additional training.