2

WORKING GROUP SUMMARIES

Symposium working groups were set up to cover four geographic subdivisions of the littoral region:

  • Harbors and Approaches

  • Straits and Archipelagoes

  • Surf Zone

  • Continental Shelves

Each working group was asked to focus on the following questions, to stimulate and focus discussion.

  1. What environmental information is needed to support special operations mine warfare, antisubmarine warfare, and amphibious operations? What are the important technical issues?

  2. Why is the environmental information needed and how is it currently applied operationally? Is there additional environmental knowledge that can be applied, immediately or over the next three years?

  3. How is this environmental information currently acquired?

  4. What are the central environmental research issues?

    1. Database issues

    2. Collection methods and priority issues

    3. Modeling and simulation issues

    4. Applications issues



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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) 2 WORKING GROUP SUMMARIES Symposium working groups were set up to cover four geographic subdivisions of the littoral region: Harbors and Approaches Straits and Archipelagoes Surf Zone Continental Shelves Each working group was asked to focus on the following questions, to stimulate and focus discussion. What environmental information is needed to support special operations mine warfare, antisubmarine warfare, and amphibious operations? What are the important technical issues? Why is the environmental information needed and how is it currently applied operationally? Is there additional environmental knowledge that can be applied, immediately or over the next three years? How is this environmental information currently acquired? What are the central environmental research issues? Database issues Collection methods and priority issues Modeling and simulation issues Applications issues

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) What research and development is needed that will have direct impact on these problems? What are the environmental research issues and warfare issues? List novel, high-risk, “far-out” ideas that could be applied. Be creative, not critical.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Report of the Harbors and Approaches Working Group Dr. David Jay, University of Washington, Chair CAPT R.C. Mabry, SWG1/NSWG, Cochair LCDR Anthony Negron, SWG1/NSWG, Assistant CAPT Charles Mauck, USNR/FNOC, Assistant The operational aspects considered were counter-mine warfare (CMW), special forces (SF), amphibious operations (AO), and antisubmarine warfare (ASW), the first three being of greatest importance in the context of harbors and approaches. The Environment Harbors and approaches are almost always identifiable as estuaries. An estuary can be defined as “a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage ” (Cameron and Pritchard, 1963). Familiar North American examples include New York Harbor, a coastal plain estuary with several adjacent tidal straits; San Francisco Bay, a river-estuary attached to a fault-formed embayment; and Puget Sound/Strait of Juan de Fuca/Straits of Georgia, a complex of river deltas, straits, and fjords. We may usefully extend the definition quoted above to include (1) tidal rivers landward of salinity intrusion to the head of the tide (e.g., the Columbia River to Portland); (2) hypersaline negative estuaries, where evaporation exceeds the sum of precipitation and river inflow (e.g., Houston's harbor and Galveston Bay); and (3) the estuarine plume outflow area, usually into an open coastal environment, where buoyancy-driven flows and stratification have a major influence on circulation and sedimentation processes (e.g., the mouth of the Amazon). These additions reflect both operational needs and the research methodology of the estuarine oceanography community. There are undoubtedly some harbors (e.g., on arid islands) that meet the quoted definition only to the extent of being “semi-enclosed. ” As a practical matter, however, the conduct of littoral warfare in these exceptional harbors would require the same information concerning tides and currents as its conduct in more typical estuarine harbors and approaches. Moreover, the presence of even small sanitary and/or industrial sewer outfalls will raise the same issues concerning

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) pollution and acoustic and electrical properties of the water column and sediments that are pertinent in estuarine harbors and approaches. The estuaries that make up the numerous harbors and approaches of the world are characterized by a great diversity of physical conditions and processes. This is true not only because there are many types of estuaries (ranging from shallow, tropical lagoons to deep, ice-bound fjords), but also because conditions within individual estuaries are extremely variable in both time and space. Salinity in a fjord may vary, for example, from zero to oceanic values across the main halocline over a few meters in the vertical direction. Salinity variability of the same magnitude may occur over a tidal cycle at a single point in space as a result of tidal advection in a salt-wedge estuary. Turbidity in a river-estuary may vary over a few hours by a factor of more than 103 because of a storm or freshet. Thus, the circulation and the electrical and acoustic properties of the estuarine environment are more diverse than those of almost any other marine environment. Fortunately, much of this variability is concentrated at a few dominant frequencies. Circulation in river-estuaries, fjords, and many other systems is controlled by tides and/or fluvial input leading to dominant tidal daily, tidal monthly, and seasonal time scales. While the influence of river flow can be unpredictable in harbors with small tributary drainage basins, river flows in large drainage basins, and particularly in those having a substantial ratio of dam storage capacity to river flow, generally follow well-defined seasonal patterns. In contrast, the atmospheric forcing that dominates many large embayments (e.g., tropical lagoons and the Ob estuary in Russia) is predictable in a statistical sense only, e.g., storms are more frequent in some seasons. How should the oceanographic diversity of the strategically important harbors of the world be handled? It is clearly impossible to study all of them; they are too numerous, and most are within the coastal waters of nations that restrict research access. It is imperative, therefore, to make good use of available information concerning dominant time and space scales of forcing. Process-oriented studies must be carried out in representative and accessible systems that are analyzed in detail. These results must then be extrapolated in a conceptually sound manner to the many important, poorly known, and inaccessible systems of the world. Coordination with other programs that seek systems-level understanding of estuarine and coastal environments would also likely be productive. These include the Land Margin Ecosystem Research program funded by the National Science Foundation and the upcoming Land-Ocean Interactions in the Coastal Zone (LOICZ) initiative of the International Geosphere-Biosphere Program.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) The variability of estuarine physical environments is reflected in biological processes. Supplies of nutrients and/or organic matter in many estuarine systems are very large relative to open-ocean values, allowing high biological productivity, a factor that strongly influences acoustic properties of water and sediment. Furthermore, estuarine biological communities are commonly, though not universally, structured by physical forcing and geochemical constraints rather than by biological processes such as competition or predation. Thus, the ecosystems that have evolved in river-estuaries, for example, are made up largely of organisms that can survive in an advection-dominated environment where the residence time of an average parcel of water (typically a few days) is much less than the generation time of most invertebrates and salinity is variable. For example, the Chesapeake Bay's ecosystem has been forced to adjust within the past several hundred years to summer anoxia imposed by high nutrient loadings. Although certain opportunistic species may appear in infrequent and unpredictable blooms, most estuarine biological populations respond to the patterns of physical variability discussed in the previous paragraph. This again points to the importance of understanding certain representative systems in some detail. We should not, as a consequence of a pressing need to deal with the short time scales directly pertinent to naval operations, lose track of the place of estuaries in recent geological history. This context is necessary to understanding the structure and evolution of estuarine ecosystems, their sedimentology, and (to the extent that channel morphology controls circulation processes) even their physics. Most estuarine ecosystems are young and rapidly evolving, because they have existed in their present form only since stabilization of global sea level about 5,000-6,000 years ago. Sedimentation rates are typically much greater than those in open-ocean environments. Estuaries on tectonically active coasts may change morphology rapidly enough to render bathymetric and tidal information obsolete within a few decades. Large expanses of bare tidal flats may become vegetated within a few years. A food chain based on large amounts of detritus exported from marshes may disappear and be supplanted by one based on river-borne detritus, with important consequences for water clarity and acoustic properties. Finally, because much of the world's population lives adjacent to estuaries, anthropogenic change is extremely important in determining the features of interest to naval operations. Estuaries are the part of the marine environment that is most accessible and susceptible to human manipulation. The direct effect of harbor dredging and construction in the form of jetties, channels, and breakwaters on tidal properties is the most obvious type of alteration. Entering the Columbia River (once the “graveyard of the Pacific”) through the maintained 48-ft navigation channel is a very different problem, for example, from that of navigating the former shifting, natural channel that had a controlling depth of 20 ft in a good year. Less direct but equally potent alterations must also be considered. Construction of the

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Aswan Dam, for example, utterly changed circulation, acoustic properties, and the sedimentation and ecosystem structure in the Nile delta. Industrial and sewage pollution in an estuary may cause a system to have completely different acoustic properties from those of nearby, unimpacted systems that would, in the absence of human population, be quite similar. Moreover, these anthropogenic changes are rapid relative to most natural changes--except perhaps those induced by tectonics. The possible use of flow regulation as a defensive weapon cannot be ignored altogether. Nationalist forces in China used dike breaches and subsequent flooding to immobilize and drown the invading Japanese during World War II, though at great cost to the native population. Artificial floods could also be used to increase stratification, decrease water clarity, and bury mines. Numerous possibilities for offensive use exist. Working Group Discussion The charge to the working group consisted of two primary tasks. The first concerned environmental information: What information is needed for littoral warfare operations, how is it presently acquired, and how can this process be improved? For the Harbors and Approaches Working Group, this issue served as a means to focus further discussion on the second topic, identification of research and development (R &D) priorities for littoral operations. Discussion in the first topic area resulted in the development of a list of information types (see Table 1). Review of this table suggested that consideration of research and technological priorities should be organized into three unifying topic areas, as follows: Tides and currents Acoustic and electrical properties of the water and sediment Pollutant and other scalar transport. Bathymetric data serve as a good example of how a specific type of data fits into the overall topics listed above. Bathymetric data are needed for modeling of tides and currents in support of all four types of operations (ASW, AO, CMW, and SF). Such data would also play an important role in evaluating acoustic, electric, and pollutant properties of the water and sediment for CMW, ASW, and SF operations, whether this evaluation was carried out through numerical modeling or more qualitative methods. The most systematic and intensive need for these bathymetric data would, however, come from numerical circulation modeling programs. Thus, we associated bathymetric data acquisition and database storage with the first research area, tides and currents. Each of the other information types can similarly be assigned to one or more of the three topics listed above. The remainder of this report is organized, therefore, in subsections focused on these areas, followed by a section presenting our Summary and Conclusions.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Table 1. Oceanographic Parameters for Littoral Warfare: Harbors and Approaches Parameter Why and How Used Current Means of Acquisition Additional Information Available Currents Mission planning, operations, maneuvering Sailing directions, pilots Availability of barotropic models Tides (heights) Mission planning, operations GFMPL, tide data base   Pollution Mission planning, protective gear, effects on swimmers, clutter density Not available, intelligence   Turbidity and color of water MCM - visual identification, NSW-Submersible operations Transmissometers, laser prototypes Remote sensing, SeaWiFS, LANDSAT Bathymetry Navigation, planning, rehearsals Charts, surveys, notice to mariners Laser, LANDSAT, better resolution needed Bottom composition and transport Navigation, planning, mine burial In situ during operations surveys, charts NRL's Remote Survey Systems Acoustic Properties MCM Detection, sonar performance, NSW counter detection MCM Sonar Performance model, data acquired on site

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) River Flows Magnetic field specification Navigation, density effects Intelligence, Army Terrain Analysis Center, surveys   Ambient Noise SDV operations (Covert), MCM maximum ranges Not available   Bioluminescence, Biologics Covert swimmer operations, safety, sonar performance Not used NAVO equipping ships to collect bioluminescence   Waves Navigation, safety, covert, MCM operations “OA” Division Limited applicability, resolution Remote sensing (airborne) Meteorology Planning, parachute operations (winds critical), boat, ship navigation, safety “OA” Division NODDS Require higher resolution models Atmospheric Refractivity Planning, detection, counter detection “OA” Division, NODDS Range dependent IREPS needed Solar/Lunar Planning, detection, navigation, night vision equipment GFMPL, PC-based Tables   Ice Navigation, planning Satellite, intelligence   GFMPL = Geophysical Fleet Mission Program Library NSW = Naval Special Warfare SeaWiFS = Sea-Viewing Wide Field Sensor IREP = Interactive Refractivity Environmental Prediction System MCM = mine countermeasures NAVO = Naval Oceanographic Office NODDS = Naval Oceanographic Data Distribution System SDV = swimmer delivery vehicle

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) It is important to note the considerable overlap of the above three topics with the traditional research agenda of the estuarine oceanography community: there is both good and bad news here. The good news is that the present state of knowledge in estuarine oceanography will allow rapid improvement at low cost insome areas, particularly the prediction of barotropic tides and currents. The bad news is that certain problems in estuarine oceanography have not been resolved by several decades of research and are of considerable fundamental difficulty. Transport of pollutants, sediments, and other materials is in this category. Consider as an example the transport of suspended matter that determines the optical properties of the water column and, in many environments, the character of the seabed itself. Existing sediment transport models uniformly fail to consider the effects of horizontal gradients in suspended sediment concentration. The rheology of liquid mud (a non-Newtonian fluid), the erosion and deposition properties of cohesive sediments, and the kinetics of particle aggregation as a function of shear, biological activity, and stratification are all poorly understood. Clearly, a sustained research effort will be required if functional models of estuarine suspended sediment transport are to be developed. Tides and Currents Improvement of knowledge in the area of tides and currents was the subject most thoroughly treated by the Harbors and Approaches Working Group. Ideas for improved prediction of tides and currents were separated into four categories: planning, operations, research problems, and desirable technology. An important conclusion for both planning and operations was that substantial improvements could be made in the near future with a relatively low investment of funds, on the basis of the existing understanding of estuarine circulation and of present models of barotropic tides and currents. There are two primary needs on the planning level. First, an estuarine classification system based on hydrodynamics should be developed that would allow division of most of the harbors and approaches of the world into about a dozen categories (e.g., lagoons, river-estuaries, weakly stratified and partially mixed bays, tidally forced fjords, and weakly forced fjords). A small suite of parameters (e.g., ratio of semidiurnal to diurnal forcing, tidal range to depth, river flow to tidal velocity, and estuary length to tidal wavelength) would then be used to place estuaries in these categories and a slightly larger number of subcategories. Representative estuaries from around the world would be classified as to category and subtype. Additional systems could be added as they became operationally important for new or potential operations. This categorization could be used focus

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) research into types of estuaries deemed to be of strategic importance and would be useful for operational purposes. This classification system would be very useful in identifying the primary sources of variance in the velocity and surface elevation, and would (as discussed below) provide additional information concerning density structure and scalar transport processes. Following is an example of the practical utility of such a system. Suppose that the barotropic tidal models discussed in the following paragraphs have been run for a particular harbor of interest, but that the river-flow and bathymetric data used in the model were of poor quality, and therefore the predicted tides and currents were of dubious validity. How much effort should be put into improving these predictions? Improvement options might include processing of remote-sensing data, covert installation of pressure gauges (not possible now, but certainly feasible in the near future), and on-site intelligence operations. If, on the one hand, we know that the system is a macrotidal river-estuary, then further efforts might well be merited, because 60 to 90 percent of the total velocity variance in such systems is normally associated with tides and river currents. If, on the other hand, the system is categorized as a hypersaline, microtidal tropical lagoon, where typically 60 to 90 percent of the current variance is related to atmospheric forcing and density currents, then further refinement of a bathymetric tidal model would likely be pointless, but modeling of wind and density-driven circulation might be imperative. A considerable improvement in the tide and current predictions presently available for many estuaries could be made by systematic application of existing tidal models on various scales. The methodology has been well proven in systematic tests in the North Sea [see Waiters and Wemer (1991) for a review]. In practice, a large-scale, regional, barotropic tidal model would be run for an entire area of possible operations. Such a regional model would usually cover at a low resolution an area the size of the North Sea, or the coastal ocean from Northern California to the north end of Vancouver Island. This regional model would then be used to formulate the open boundary conditions for models of individual estuaries or related groups of them. Examples of river-estuary systems suitable for regional models would be the Rotterdam Waterway and the Puget Sound/Strait of Juan de Fuca/Straits of Georgia complex. The smaller-scale models may be either two- or three-dimensional, and adapted to the character of the particular estuary; such models might include, for example, wetting and drying of tidal flats, fluvial forcing, and sophisticated turbulence predictions, as appropriate. Given reasonable bathymetric data and proper boundary forcing, existing barotropic tidal models can predict tidal

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) elevations within a few percent and barotropic tidal currents within plus or minus 10 percent. For many harbors and approaches, barotropic currents account for the bulk of the total velocity variance. In other cases--for example, river-estuaries-nonlinearities related to time variations in the density field create internally forced modes that greatly modify the barotropic tide. These differences again emphasize the importance of a classification system: it would allow identification of systems for which existing barotropic models are, or are not, adequate for current prediction of currents. A rather different modeling approach is needed within an actual theater of operations. The analogy to oil-spill modeling is appropriate here. Model predictions must not only be accurate and timely, but the modeling system must be relatively easy to use and needs to be capable of being run with assimilation of observations in near real time. Experience with oil-spill cleanups suggests that if operational models do not have these characteristics, they will be ignored in favor of tide tables and seat-of-the-pants reasoning. Theater operational models should also be relatively small scale, and should run on microcomputers or work stations. They would be connected to large, regional planning models through a network. As data are acquired in the course of an operation, they should be incorporated into a geographic information system (or other similar) database and used to improve model predictions. Relevant data might include bathymetry, velocity profiles from shipboard Acoustic Doppler Current Profilers (ADCP), tidal elevation from moored pressure gauges, and information concerning sediment type and bottom roughness. These data should also be sent by network back to the regional planning center so that the larger regional model could also be modified as data were acquired. Prediction of tides and currents is straightforward for harbors and approaches only in the absence of strong interactions with other flow processes such as river flow, wind waves, and atmospherically-forced currents. If both tides and one or more of these factors are important in a system, the resulting interactions raise fundamental, unresolved questions in estuarine oceanography. Estuaries with both strong tides and strong river flow, for example, have time-varying stratification that drives substantial, nonlinear circulations that are poorly understood at present. Interactions of tidal currents with swell can substantially modify the tidal current and greatly increase wave amplitude. Prediction of these wave-current interactions is still an imprecise art. Better turbulence models that account correctly for mixing due to free-shear layer instabilities and internal wave interactions are essential to the construction of improved models of stratified tidal flows that could properly represent the nonlinear processes mentioned above. Analyses of time series of current and pressure observations need, furthermore, to be improved in light of recent advances related to nonstationary

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Oceanographic Tides -Effects of local wind stress Internal Waves * Currents Surface Subsurface Water temperature * Salinity/conductivity Freshwater run-off Sea state Wave height and direction Surf conditions * Optical properties (vertical and horizontal) * Absorption (dissolved and particulate organic matter) Turbidity Bottom pressure Ice conditions Bubbles Bathymetric and Topographic Bottom and beach slope Beach composition Bathymetric features Reefs Bottom obstructions Rivers and estuaries Harbors Coastal terrain Soil types Vegetation types Acoustic * Scattering and reverberation * Sound speed profile Ambient noise * Transmission loss Geophysical/Magnetic * Bottom roughness Bottom type Sediment property gradients Clutter (acoustic and magnetic) Sediment conductivity Sediment gases Geoacoustic properties * Bottom strength and stability Pressure wave transmission (Shock wave propagation) Ambient magnetic background * Ambient electrical background Anthropogenic * Pollution Noise Obstructions Bottom clutter

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Littoral Operations Requiring Environmental Data, Data Presently Available, and Additional Data Requirements Cross-Cutting Issues Cross-cutting issues affect all, or at least more than one, type of naval operations in the littoral zone. Environmental or data-gathering issues that are more specific to mine countermeasures, antisubmarine warfare, special operations, or amphibious warfare are discussed in separate sections below. Sufficient characterization of coastal regions is needed to permit advance operational planning. For example, the range of weather conditions, currents, water temperature and density, or bottom conditions that might be encountered could be provided, along with information on probabilities of encountering environmental conditions within that range. Such information should indicate correlations or cause-and-effect relationships among environmental variables. For example, a change in wind direction could lead to changes in sea surface currents and in temperature and salinity distributions. At present there is a limited understanding by naval personnel of nonacoustic environmental information and how it could be used in making tactical decisions. For example, the appropriate tactical response to information on the distribution of bioluminescence, suspended particulate matter, or zooplankton and nekton is not clear. Research to provide more and better environmental information is a vital first step, but this must be coupled to education of naval personnel in the use of the data. There is a general need for performance prediction and assessment for all sensors deployed in naval operations, but in particular for sonar and radar. The availability of information on the accuracy of sensors under any given set of environmental conditions is one key aspect. Also, important, of course, is the availability of the necessary environmental data. Another priority is the minimization of risk to naval personnel, which in general also means that an increased capability for assessment and prediction of environmental conditions is needed. In addition, new remote or robotic approaches to operations such as covert data gathering and mine detection and neutralization must be developed. One of the most difficult problems in environmental prediction and assessment is the conditions encountered by advance personnel such as special forces and amphibious forces. By their nature, these forces must enter areas that have not recently been accessible for study except by remote sensors. Workshop participants indicated a need, in general, for instruments that can measure key environmental properties during naval operations and provide useful

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) information in real time. Ideally these instruments would be small, rugged, and compatible with a variety of platforms, including helicopters, surface ships, submarines, and AUVs. Both passive and active sensors should be considered. Expendable or highly portable instruments would be especially valuable to advance forces. Because of the spatial and temporal variability of the littoral zone and because of rapidly increasing data-gathering efforts and capabilities, data handling, archiving, and dissemination will require new approaches. It simply will not be possible for the Navy to retain all the data that will become available. The high temporal and spatial variability of the continental shelf will require assimilation of different data sources, with different spatial and temporal resolution, into databases. Assimilation of data, with varying resolution, into models and “ nesting” of high-resolution littoral models into lower-resolution oceanic models also pose significant problems. Issues that must be addressed include these questions: (1) What kinds of data are needed, at what spatial or temporal resolution? (2) What quality-assurance and quality-control procedures should be implemented? (3) What is the required spatial and temporal resolution of models? (4) What is the required accuracy of model predictions? (5) How can data or model predictions be provided to naval personnel, rapidly and in the most useful form? Mine Countermeasures Mine burial prediction models, including the processes of burial due to impact, scour, migrating sand ridges, and deposition, require development or improvement. At present, impact models are the only type available, and they do not provide sufficiently accurate predictions. A better fundamental understanding of benthic boundary layer hydrodynamics and sediment transport is essential. Data needed to constrain such models is also lacking; new, high-area-coverage remote-sensing techniques to gather the required data are needed. Mine detection and classification, especially for buried mines, remains a challenge. Acoustic techniques have promise, but environmental information is essential for developing and predicting the performance of these sensors. Such information is needed on the following subjects, for example: spatial and temporal coherence of the medium; ambient noise from breaking waves, bubbles, organisms, or precipitation; volume scattering due to bubbles or suspended particles; and the shock wave propagation mechanism in sediments. For high-frequency mine classification, information on density, microstructure, and internal waves is needed. The potential of magnetic and electrical sensors needs further evaluation.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) For all mine detection, classification, and neutralization operations, there is need for a package of selected environmental sensors that can be deployed by various platforms and which will operate unattended for several days. This capability would provide information about the temporal variability of the selected parameters. The suite of sensors would need to include magnetic and acoustic sweeping gear and output detectors for determining whether the sweeping gear was operating up to specifications. The package should be deployable from iron surface ships, helicopters, submarines, and Sea, Air, and Land (SEAL) special warfare units, or installed on AUVs. Antisubmarine Warfare Both passive and active sonar performance prediction and assessment capabilities in shallow water are essential, even if extensive local databases are not available. For low-frequency detection, in the range 20 to 200 Hz, bottom loss and reverberation must be better understood to yield improved range predictions. Hydrophones on the bottom will respond to various interfacial waves that travel on or near the water-sediment boundary. Will this phenomenon provide useful information, or should the hydrophones be deployed above the bottom to reduce this signal? Shallow-water acoustic ducting, when it exists, is critically important to submarine detection and localization. There is a need for more historical and synoptic knowledge of when and where such ducting might occur. Ships or submarines may stimulate organisms to emit acoustic signals. Understanding of this phenomenon could lead to a new means of passive detection. For active sonars at medium frequencies, measurement and prediction of reverberation are important problems. If the sound speed profile is neither positive nor strongly negative, the sound field will depend on bottom reflection and scattering coefficients, which depend on bottom composition and roughness. These could be determined experimentally in selected areas. Another key environmental characteristic is the distribution of organisms in the water column. A means of covertly assessing volume scattering is needed, as well as predictive models. It is not known whether shallow-water acoustic field calculations using 2.5-dimensional models will be sufficiently accurate or whether three-dimensional models will be required. High-frequency volume attenuation in shallow water will limit or enhance certain acoustic detection techniques. There is need for more historical and synoptic knowledge of such attenuation values at frequencies of 25 to 300 kHz. Single acoustic probes should be evaluated for collecting essential data in remote areas. For example, can an approximate sound speed profile and bottom reflection and scattering coefficients be obtained from a single explosive charge

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) and receiver? Also, useful information might be obtained by means of active sonar devices, for example, expendable “pingers.” Passive or relatively undetectable atmospheric sensors for forward data collection would be useful. Sensors capable of measuring vertical temperature and humidity profiles along a path to a potential target have particular application to ASW, allowing prediction of evaporative duct height or submarine electronic sensor module capability and vulnerability. Such sensors could also allow range-dependent Radar/radar sensor module performance predictions. Aerosols impact the performance of infrared, visual, and laser systems. Vertical total wind profiles are needed to predict aerosol distributions. Sea surface roughness affects the performance of radar and optical sensors. A potential new approach to assessment is the use of over-the-horizon radars, modified from those now used for drug interdiction. Special Warfare and Amphibious Operations Assessment and prediction of subsurface currents is a particular need for the Naval Special Warfare Command, although they are also important to other aspects of littoral warfare. Hull-mounted or bottom-deployed (and upward-looking) ADCPs can provide extensive current data over depth profiles of up to about 300 m, although there are two practical limitations to widespread use, cost and data management, that must be overcome. Prediction, especially of high-frequency variations in currents, will require an improved fundamental understanding of shelf dynamics. Density fields and variations due to processes such as internal waves are important to special operations. These affect activities such as exit of divers from submarines. Assessment of density is straightforward, but, again, prediction of temporal and spatial variations will again require improved understanding of fundamental physical oceanographic processes. Marine life is much more abundant in the littoral zone than in the open ocean, and thus biological factors have more influence on littoral naval operations than those in the open ocean. However, present knowledge of several important biological phenomena is inadequate. For example, bioluminescence stimulated by turbulence can either be a useful tool for tracking hostile vessels or a dangerous “marker” of the Navy's assets. In either case, at present the distribution of bioluminescent organisms in space and time is unpredictable. There are no strategies available for avoiding or mitigating bioluminescence, or, on the other hand, for exploiting it. Other biological phenomena with potential operational significance include biological obstructions such as reefs and kelp beds, alteration of bottom-sediment physical properties and stability by benthic organisms,

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) biofouling of mines to avoid detection, and biofouling and resulting impaired performance of deployed sensors. Pollution is of concern to special forces and amphibious operations from several perspectives. For example, divers or amphibious personnel may be exposed to hazards due to poor water quality. Diseases such as cholera can be contracted by swimming in sewage-contaminated waters, and some coastal waters may be contaminated with highly toxic industrial wastes. On the other hand, negative impacts on public opinion can result if naval operations cause environmental damage. Research Needs Overview The environment of the littoral zone is distinct from that of the open ocean, and it presents many special challenges to naval operations. For example, radar, sonar, and other sensors developed for use in the open ocean are less effective in the coastal ocean. To adapt these to use in continental shelf regions, more and better information on the environmental factors that govern sensor performance is needed. Development of new sensors, or sensors newly applied to Navy problems, could be of great value. However, in some cases, research to characterize the environment is an absolute prerequisite to sensor development. Research to understand better the fundamental oceanographic processes responsible for key environmental variables must underpin research targeted on specific problems such as sensor performance in a particular region. More and better environmental data from littoral zones is needed, but it is even more important to place these data in a context of research that will lead to an understanding of the processes which yield and interrelate atmospheric, oceanic, and seafloor properties. Research effort should initially concentrate on the collection of data required for better understanding of shelf processes and for the development of modeling capabilities. Work can then proceed to the development and validation of coastal ocean prediction systems, which incorporate enhanced models with the capability to assimilate environmental data. Sufficient knowledge of the littoral environment to predict the usefulness of new or improved sensors must be obtained before substantial effort is expended on sensor development. Although many examples of this need could be given, the working group discussions focused on underwater electromagnetic field measurements and remote sensing of salinity.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Electromagnetic Field Measurement One of the more promising shallow-water surveillance and mine countermeasure technologies is based on the detection of the electromagnetic fields produced by ships and submarines. These fields are generated by corrosion-electric currents due to the dissimilar metals used in the hull and shaft/screw, and may be enhanced by passive and/or active anticorrosion efforts, for example, by the use of sacrificial anodes. The electromagnetic signatures of ships and submarines, which typically have characteristic frequencies in the 0.1-to-0.001-Hz range, have characteristic shapes that can yield direction information and are detectable at ranges of several kilometers on the shelf. In addition, the corrosion current dipole can be modulated by the rotating shaft to produce higher-frequency signals that can propagate even farther. Electromagnetic (EM) signals are enhanced in shallow water as compared to those in the deep ocean, and their attenuation with range is substantially weaker. The Navy is investing substantial sums in improving EM sensors and devising rapidly deployable systems utilizing these technologies. Signal processing schemes are also being devised. These efforts are being conducted in the virtual absence of basic information on the ambient EM environment. What are the natural sources of EM fields, what are their coherence scales, and what are their magnitudes? This information is essential for devising physics-based noise cancellation procedures and determining the level of sensor performance that is needed, compared with what is achievable. In the absence of basic information on the EM environment, there is a real danger of prematurely discrediting the EM method due to improper consideration of the physical problem. What is needed is a basic effort to characterize the sources of EM fields in typical shallow-water environments. The most important generating mechanism is hydrodynamic, that is, the Hall effect. The possible sources, such as surface waves and internal waves, are both numerous and spatially variable. A series of focused array experiments in diverse environments, utilizing EM sources together with measurements of variables related to the hydrodynamic sources, is essential. This will lead to a predictive capability that feeds back into sensor and system design and to quantitative prediction of performance. The Navy should not expend extensive efforts on improving sensor sensitivity in the absence of information on environmental noise. The capability of EM systems is not sensor-noise-limited, but rather environmental-noise-limited. Remote Sensing of Salinity New approaches to remote sensing of key environmental variables need to be explored. For example, salinity is much more variable spatially and temporally in the littoral zone than in the open ocean. Although it is readily measured from surface ships using conductivity sensors, there is no technique for remote

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) measurement from aircraft or satellites. However, there is a potential approach to remote sensing of salinity that involves measurement of the fluorescence or light absorbance of dissolved organic matter (DOM). This is possible because most rivers contain larger quantities of DOM than seawater does, and fluvial organic DOM absorption and fluorescence spectra differ from those in a marine environment. The fluvial DOM signature could also provide a remotely detectable tracer for surface-water circulation in the coastal zone. Some basic environmental data are needed to evaluate the potential of this technique. Correlations of salinity versus DOM concentration and absorbance/fluorescence spectra should be determined for a variety of rivers. Also, the sensitivity of the DOM signal to salinity variations needs to be established. Based on the optical properties of fluvial and marine DOM, sensors could be developed to optimize their discrimination. Important General Issues for Future Navy Operations in the Littoral Regime Fundamental Differences Between the Littoral and Oceanic Environments Must Be Recognized. In the past, large environmental databases and predictive models have served an important purpose in naval operations in deep-ocean basins. In contrast, in the dynamic shelf environment, the extent to which such approaches will be useful is not clear. The danger in using approaches suited to less dynamic, open-ocean systems is that such models could “invent” an average shelf environment which is far from reality at any particular time or place. An important, first-order task for mine countermeasures and antisubmarine warfare in shelf areas is to identify the environmental properties that can in principle be mapped or predicted and those that cannot. A refinement would be to assign accuracy estimates or confidence levels to predictions. Certainly, predictive capabilities can be increased with gathering of more or more accurate data and with improved models. However, in a dynamic area such as the shelf, the time and space scales of variability are such that many environmental characteristics will not be predictable in the long term, either by amassing a large, retrospective database or by modeling. A new paradigm is needed that recognizes the temporal and spatial variability of the shelf and leads to innovative scientific and engineering approaches to the support of naval operations. Oceanographic Processes of the Shelf Must Be Understood. Basic research is needed to improve predictive capabilities for shelf circulation features relevant to the Navy's littoral warfare mission. Effort should focus initially on existing dynamic modeling capabilities, used in conjunction with

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) existing data sets, with the ultimate goal of constructing a three-dimensional, time-dependent coastal ocean prediction system that can be applied in a series of verifying field experiments. Research must be designed with awareness of the high degree of spatial variability on the shelf. Relevant issues are as follows: Given limited measurements, how well can we model or predict oceanographic variables relevant to littoral warfare? At present, some predictive capability exists for tides, surface waves, and low-frequency alongshore velocity, but there is no corresponding predictive capability for cross-shore flow and the three-dimensional density structure over the continental shelf. Also, the existing understanding of mean flow, over time scales of days to weeks is more complete, than of higher-frequency variations such as those due to tides. Understanding of the basic temporal and spatial correlation scales as a function of shelf regime is required. c. Increased understanding of the behavior of the surface and bottom turbulent boundary layers on the shelf is needed. In particular, the bottom boundary layer is a key region because of resuspension of sediment and its effects on water clarity and mine burial. What is the best way to assimilate data obtained by air-deployed and/or covert underwater sensors into fully three-dimensional, time-dependent shelf circulation models? This is essential for construction of a coastal ocean prediction system that should eventually include biological and suspended-sediment submodels for addressing water clarity. It is essential to evaluate model systems and prediction with a sequence of field experiments on several types of continental shelves, perhaps most usefully in conjunction with Navy exercises. The Navy research effort should initially concentrate on important shelf circulation processes using existing modeling capabilities and data sets, then proceed to coastal ocean prediction systems that incorporate both models and observations. The recommended research will facilitate the transition of academic expertise to the applied and operational communities concerned with littoral warfare. Sensor performance is dependent on multiple processes occurring on different time and length scales. Is there a correlative relationship between larger-scale and small-scale patterns? The time and length correlation scales for a variety of frequencies need to be determined. A database approach may be successful for large-scale processes and low-frequency acoustics but is unlikely to be usable for mesoscale and small-scale processes and higher frequencies. To use medium-high and high-frequency sensors, a first-principle understanding of the link between

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) oceanographic processes and sensor performance is needed. For example, research is needed to determine how wave fields and sediment properties interact to produce bottom roughness, and how bottom roughness is related to sound reverberation and scattering. Multidisciplinary Field Experiments Should Be Conducted. One or more field experiments in U.S. waters are needed to assess the abilities and performance of existing and developing technologies to support littoral warfare in water depths from 40 to 1,000 meters. Both observations and modeling conducted in connection with such an experiment should include marine, atmospheric, and coastal land environments. An important goal of this experiment should be to transfer academic capabilities and expertise to the applied and operational communities supporting littoral warfare. This exercise could also be a test of the proposal to establish “regional oceanographic experts ” within the operational community. Another key goal should be to “calibrate” the ASW/MCM capability of tactical units and surveillance assets under a variety of well-characterized environmental conditions. These field experiments could also be used to test performance-prediction models for acoustic or nonacoustic sensors. Ideas for Collection and Use of Environmental Data for Operations in the Littoral Environment The working group assembled a list of ideas for naval operations, or environmental data collection or utilization in the littoral environment: Sensor Performance Assessment - Assess passive and active sonar performance in situ. Sensor Confusion - Confuse enemy acoustic sensors by deploying acoustic decoys--for example, devices that emit submarine or ship noises at a point distant from the actual location of the asset or that disguise active sonar as ambient noise. Environmental Assessment - Expand environmental data collection by naval and research vessels operating in the littoral zone, and assimilate that data into a littoral database; combine sidescan sonar with a chirp sensor in order to obtain information about bottom roughness and volume heterogeneity; use radar reflection as a means to obtain information about surface currents over large areas from ships; and measure bioluminescence and light transmission remotely using satellite or aircraft-borne sensors or an in situ (deployable) sensor.

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PROCEEDINGS OF SYMPOSIUM ON COASTAL OCEANOGRAPHY AND LITTORAL WARFARE: (Unclassified Summary) Assessment or Prediction of Hostile Activities - Use covert sensors to detect hostile mine-laying operations; locate mines or submarines via the fluorescence of synthetic organic chemical components; predict mining tactics--for example, “seeding” of currents with floating mines; and use a remotely-operated vehicles to survey activities off known submarine ports. Environmental Databases and Their Exploitation - Develop a process-oriented database that is verified by fleet and academic data collection; maintain a person knowledgeable about environmental conditions and effects aboard all fleet assets, and provide that person with appropriate data and training. Working group participants were struck by the contrast between the substantial naval expertise and data availability in meteorology and the much smaller utilization of oceanographic expertise and data. Summary and Conclusions The Continental Shelf Working Group identified the set of environmental factors of most importance to Navy operations in the littoral zone. The working group also identified a number of cross-cutting issues that are important for operations in more than one of the four littoral areas examined in the symposium. These issues included the need for sufficient characterization of coastal regions to permit advanced planning, a better understanding by naval personnel about how to use nonacoustic environmental information for making tactical decisions, information about the accuracy of sensors under any combination of environmental conditions, limiting risk to Navy personnel by using more remote methods and predictions, the need for real-time sensors of environmental properties, and new approaches for data handling, archiving, and dissemination. The working group also noted relevant problems in mine countermeasures, antisubmarine warfare, special warfare, and amphibious operations that could benefit from increased research effort. Finally, this working group listed a set of key research needs to improve operations in the littoral zone, highlighting the need to acquire basic environmental knowledge before sensor development is pursued. The discussions and recommendations of the Continental Shelf Working Group often reiterated the theme that the continental shelf is extremely dynamic, with a high degree of variability in space and time. New approaches, not just more data, are needed to characterize this environment. However, it should also be emphasized that the continental shelf is bounded by the open sea, and much of our present and developing understanding of the shelf region builds upon the research results and research techniques of basin oceanography.