Many attributes of the underwater environment interfere with the detection, characterization, and recovery of military munitions. Except at very shallow sites, munitions underwater are difficult to access. Conditions interfere with the ability of sensors to detect and characterize them and remediation is more difficult.
In many cases, much is unknown about underwater munitions sites. Whether munitions will be found on the seafloor, partially buried, or completely buried in the sediment is determined by the site’s past uses and its conditions. Dynamic conditions can result in mobility of munitions, as well as repeated burial and scour. In some environments, corrosion and biofouling may affect their detection or remediation. In most cases, the relative abundance of intact munitions and munitions-related debris, such as fragments, scrap, and remains of targets, are unknown.
The geophysical sensors used to detect UXO on land are more limited in their application underwater. The rapid fall-off of their signal with distance from the target is overcome on land sites by deploying the sensors within close proximity of the ground surface, a tactic not possible at most underwater sites. Traditional acoustic sensors can operate effectively with larger stand-offs from the bottom, but they are most useful for munitions proud of the bottom and they are often confused by non-munitions clutter. Low-frequency acoustic sensors may overcome these problems but they have not been demonstrated in realistic environments. Optical sensors have limited applicability in turbid waters or against fully-buried munitions.
Sensor platforms for underwater use are more complex and difficult to operate than typical land systems. Towed systems can be used to moderate depths. For deeper sites, ROV and AUV technologies may be required. For either platform, careful control of platform orientation and stand-off is required to collect quality survey data. This is not a trivial achievement. In addition, geolocation of the sensor system, and thus the targets detected, is difficult underwater.
SERDP and ESTCP are supporting research and development projects in the following areas:
Wide Area Assessment
Rapid assessment of large areas to identify concentrations of munitions and areas free of munitions is needed to support site management decisions or the initial steps of a response program. In contaminated areas, data are needed to define the nature and extent of munitions contamination. Investments focus on developing and demonstrating a suite of technologies to be used for a variety of site conditions.
Individual munitions must be detected with high probability and sufficient location accuracy, in order for them to be identified and retrieved. Technologies to conduct detailed surveys of munitions response sites in the underwater environment are limited by water depth, water turbidity, and sea state. Thus far, these methods have not achieved reliable detection of small munitions nor discrimination of munitions from harmless clutter. Investments are aimed at addressing these shortcomings.
Recovery and Disposal
The remediation of UXO underwater presents numerous challenges. Current practices employ divers for manual retrieval of targets, a dangerous and costly practice. Also, items that have the potential to explode in most cases cannot be moved, but blow-in-place operations can harm marine life. Investments focus on cost-effective, safe, and environmentally acceptable recovery and disposal.
Storm waves or currents can cause munitions underwater to bury, become unburied, or move into new, potentially dangerous locations. SERDP is supporting research to understand these processes and, ultimately, lead to a simplified model to predict them. Both laboratory and in situ measurements of munitions behavior are being conducted to support development of a predictive model and validate that model once completed.
Phenomenology refers to the characteristics of munitions and site conditions in an underwater environment. Such factors include the location and condition of the munitions, the munitions’ position in relation to scrap and other sources of clutter, and specific site conditions, such as salinity and turbidity. A better understanding of how these characteristics and conditions can affect munitions detection and remediation is needed. Focus is on improving technology performance and site management.
Burial and Mobility Modeling of Munitions in the Underwater Environment (2014)
SERDP/Office of Naval Research Workshop on Acoustic Detection and Classification of UXO in the Underwater Environment (2013)
Technology Needs for the Characterization, Management, and Remediation of Military Munitions in Underwater Environments (2007)