Oceanography and Mine Warfare (2000)

OAS Science and Technology is divided into two divisions. The first is the Sensing and Systems Division, which manages research related to Navy and Marine Corps operations, including mine warfare. The following are summaries of research and technology development of special interest to mine warfare.

The Ocean Acoustics Program supports research that addresses the physics of generating, propagating, and scattering narrowband and broadband acoustic (and elastic) waves in the ocean environment. This program encompasses three primary research areas:

• Shallow water acoustics, which aims to understand the propagation and scattering of low-frequency (10Hz to a few kHz) acoustic energy in the nearshore ocean environment. Areas of research include investigations of shallow water scattering mechanisms, the conversion of seafloor-incident acoustic energy into elastic body waves and interface waves, and acoustic propagation through linear and nonlinear internal waves.

• High-frequency acoustics, which seeks to understand the interaction of high-frequency (few kHz to MHz) sound in the ocean environment, including the propagation of sound through an intervening turbulent or stochastic medium; scattering from rough surfaces, biologies, and bubbles; and penetration and propagation in the seafloor.

• Long-range propagation, whose goal is to understand the behavior of long-range sound propagation (several hundred kilometers to several thousand kilometers) in the ocean. The main area of study concerns the effect of internal ocean waves and mesoscale waves on transmitted broadband acoustic signals.

This research program investigates physical and chemical processes governing Earth surface scattering of active and passive electromagnetic radiation and the propagation of this radiation through the upper atmosphere and the near space environment. Remote-sensing research is directed toward development of clutter models and automatic target recognition. Additional research interests include studies of electromagnetic scattering theory, microwave properties, scattering surface characterization, and wave and flux modulation mechanisms.

Research in the Coastal Dynamics Program includes aspects of coastal ocean fluid and sediment mechanics. At present, three research areas are emphasized:

• Inner-shelf dynamics: fluid mechanics of the continental shelf, particularly the inner shelf, seaward of the surf zone, where surface and bottom boundary layers influence much of the water column;

• Nearshore processes: fluid dynamics, fluid-sediment interactions, and the resulting morphological response in the nearshore, where waves begin to break because of shoaling; and

• Surface waves: the fluid mechanics of coastal surface waves and methods for improved prediction.

New initiatives will explore bay, estuarine, and river-mouth dynamics, including the interaction of water depth, tides, winds, and water column stratification. Research and development collaborations with other programs help address such issues as coastal meteorology, coastal zone remote-sensing, shallow ocean modeling, and mine burial and migration. Particular interest is placed on the use of remote-sensing techniques that can be used to augment limited or minimal in situ field measurements.

This program focuses on multidisciplinary science and technology research on the behavior of ocean systems, particularly the coupled nonlinear interactions of fluids with generic structural components and unmanned platforms. Development is primarily in: detection and imaging techniques applicable to underwater and buried objects; techniques for neutralization of explosive devices; underwater life support technologies; surface and subsurface transport systems for Navy Special Forces; technologies for coastal zone mobile autonomous platform systems; and capabilities for rapid clearance of mines and obstacles from the surf zone.

Mine reconnaissance is concerned with determining the presence of mines and obstacle fields and their densities and boundaries. The current focus of funding is on clandestine reconnaissance to enable data collection in the battlefield while preventing enemy forces from deciphering naval strategies prior to an amphibious assault. Acoustic minefield reconnaissance, would benefit from the use of underwater vehicles carrying appropriate minehunting sensors. Sensor and signal-processing approaches that support and/or facilitate high-area minefield search rates while providing sufficient clutter rejection in the coastal zone is of high priority, particularly in shallow water and very shallow water. Other efforts of high priority include synthetic aperture sonar, side-looking sonars, ahead-looking sonars, and algorithms to automatically detect, classify, and identify individual mines.

Current minehunting systems are time consuming, as they operate at a lower resolution than mine detection sensors. Thus, a significant amount of time is spent positioning near the target. Consequently, a high-priority research effort is the development of sensor and signal-processing algorithms to provide classification at ranges comparable to those of detection.

A new principle of minehunting being developed capitalizes on recent breakthroughs in acoustic modem communication technologies. Essentially, a large number of small, cost-effective underwater vehicles operating in parallel, equipped with high-baud-rate modems, are deployed in a region. A network of fixed acoustic buoys or nodes controls their dispersal, and the position of each candidate mine-like object is transmitted to the vehicles. An underwater positioning system, controlled by the buoys or nodes, acts similarly to Loran C, so that no transmissions from the vehicles to the nodes are required for positioning. Re-acquisition of targets is minimized, and the underwater vehicles determine the nature of the target. The result of this identification is then transmitted to the acoustic nodes, which relay the data to a central command and control system aboard a ship safely out of the minefield. The concept

of a multiplicity of vehicles, acoustic nodes, and underwater positioning should radically reduce the time necessary to perform minehunting, and set the stage for mine neutralization. At present, ONR is actively soliciting new proposals to pursue all or part of this system, particularly the development of sensor technologies.

Mine neutralization is time intensive and requires putting humans at risk. In shallow water regions, remotely operated vehicles (ROVs) can be used, but the time spent deploying and recovering these systems prevents the in-stride capability desired by the Navy and Marine Corps. This ability to clear mines and obstacles in-stride remains a critical science and technology challenge that has not yielded a straightforward solution. High-priority efforts include novel approaches to neutralizing floating, moored, buried, and bottom mines in the coastal zone.

The goal of the Processes and Prediction Division of OAS S&T is to ensure the collection of environmental data, develop and improve the understanding of environmental variability, and increase the limits of predictability by using quantitative models. This division plans, fosters, and encourages an extensive program of scientific research and technological development in the following fields of interest to mine warfare.

The aim of the Environmental Optics Program is to further the understanding of how light interacts with the water column, ocean boundaries, and the atmosphere near the ocean surface. Specific areas of study include radiative transfer modeling, instrument development, optical process studies, and coastal remote-sensing.

The products of these research areas support the development and application of ocean prediction models, new ocean remote-sensing systems, and associated image analysis algorithms. Applied research in support of mine warfare and special operations is funded in areas of underwater imaging and hyperspectral remote-sensing.

The objective of this research program is to support process-oriented, hypothesis-driven physical oceanographic research to provide tools and techniques that can be adapted for fleet use. In response to post-Cold War naval strategy and tactics, increased operational importance is being given to the coastal zone. Consequently, research emphasis is on the integration of circulation theory and modeling in nearshore environments. There is also a strong emphasis on interdisciplinary research. The primary objective of the program is to foster the transition of research products, such as numerical and theoretical models, analysis algorithms, in situ data, and seagoing instrumentation, into operational naval systems.

The goal of the Biological Oceanography Program is to provide information on the distribution, growth, and abundance of biota in the coastal ocean and sediments by understanding how biota influence operationally important optical and acoustical properties. An important aim of the Biological Oceanography Program is to improve observational capabilities at small-to-meso temporal and spatial scales (minutes-weeks, cm-km) and enhance the understanding of processes affecting biological phenomena. These capabilities will enable the development of new instrumentation to sample and observe biological processes and will aid in modeling coupled biophysical and biooptical phenomena in the coastal ocean and shallow water sediments.

The aims of the chemical oceanography program are to develop predictive capabilities for chemical distributions and speciation in marine environments, especially as they relate to optical and acoustical properties of seawater; to monitor and understand chemical reactions impacting environmental quality; and to develop new in situ chemical sensors for accurate and rapid detection of key chemical species at low concentrations. Specific research

projects include investigations on the occurrence and production of colored dissolved organic matter in the coastal ocean, air-sea gas exchange processes, aerosol chemical dynamics, chemistry of trace elements in the upper ocean, nutrient dynamics, and heavy metal speciation in sediments.

This research program seeks to develop accurate temporal and spatial quantitative models of ocean systems. Underlying fundamentals include ocean field estimation; scale and boundary interactions applied toward ground-truthing and forecast skills; subgrid-scale parameterization; and development of models incorporating oceanatmosphere, ocean-bottom coupling, and nested domains. The goal of enhanced predictability is achieved through research on better dynamic formulations, improved numerical methods, and optimal data assimilation through adaptive sampling. Basic and applied research are pursued jointly to improve strategic and tactical decisions using environmental information and to motivate new understanding by operational experience.

The Marine Geology and Geophysics Program, in line with changing naval operations, has increased its interest in nearshore studies and is undertaking substantive efforts in continental shelf research. One such effort is the Strata Formation on Margins (STRATAFORM) Program, which seeks to understand the creation of the continental shelf and slope stratigraphic record as a product of geological processes acting with spatial and temporal heterogeneity. This understanding will lead to the development of models capable of predicting stratigraphic patterns on a variety of continental margins. Overall, the program goal is to increase the understanding of mechanisms controlling the structure, history, and dynamics of geologic features, which in turn affect sound propagation, seafloor instability, bathymetry, and electromagnetic transmissions in the water column and ocean bottom.

The objective of this research program is to sponsor integrated basic, applied, and developmental research to improve the modeling and prediction of meteorological parameters critical to naval platform, sensor, and weapons performance. The program includes research and development leading to enhanced environmental support for operations, training, mission planning, and systems development. Specific research interests include investigations of:

• mesoscale coastal phenomena, including data assimilation protocols incorporating high-data rate, asynchronous sensors (radar, Light Detection and Ranging [LIDAR], etc.);

• global, mesoscale, and on-scene modeling that focuses on the marine atmosphere and coastal zone;

• simulations to visualize weather phenomena; marine boundary layer processes, including aerosols and clouds; and

• environmental effects on electromagnetic and electro-optic propagation, and tropical cyclone behavior, including the evolution of motion and structure.

The Mine Countermeasure Program Office is also in the OAS S&T Department. This office is the focus of the Navy's science and technology efforts with regard to MCM. There are currently two main initiatives in this program office: the Joint Countermine Advanced Concept Technology Demonstration (ACTD) and the emerging Enhanced Naval Capability Initiative in Very Shallow Water Organic Mine Countermeasures. The objective of these projects is to develop seamless sea-to-land amphibious MCM operations.