In the underwater environment, conditions interfere with the ability of sensors to detect and characterize UXO and remediation is more difficult. 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. The relative abundance of intact munitions and munitions-related debris, such as fragments, scrap, and remains of targets, are unknown.

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 any platform, careful control of orientation and stand-off is required to collect quality survey data. Geolocation of the sensor system, and thus the targets detected, is difficult underwater.

All sensor modalities are under consideration. DCL (Detection, Classification and Localization) systems include acoustic, electromagnetic, magnetic, and optical sensors. 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 overcome these problems and they have been demonstrated in realistic environments. Optical sensors have limited applicability in turbid waters or against fully-buried munitions. Magnetic devices detect the presence of iron-based targets, but do not provide classification. Electromagnetic Induction (EMI) sensors, very successful in terrestrial conditions, require close proximity to function well, which is a challenge in the marine environment.