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In June, 2004 and February, 2007, in field tracer studies were conducted on the Hollywood and South Central outfalls, using sulfur hexafluoride (SF6) as a tracer. The objective of these studies was to determine if the tracer could be detected in the farfield at significant distance, and if so, could this data be used to construct a model of the farfield plume. Prior models for farfield plume movement do not appear to comport well with the conditions in southeast Florida. Extensive research was conducted in southeast Florida on 4 outfalls, which led to the development of nearfield dilution equations for same. However farfield modeling of outfall plumes was difficult to accomplish because the tracers used are not detectable for significant distances. The SF6 resolved that problem and as a result the Hollywood outfall was used to construct a model. Two methods were investigated for modeling the plume, 1) the Eureqa formulation method and 2) the Gamma-Curve method. The concentrations in the x-y plane were first found by using the Eureqa formulation to calculate the concentration at each grid point given its depth and the concentration of the centerline at the same latitude. The plume models were generated using MATLAB that matched with the results actually seen in the field.

Pathways and dilution of a point source ocean discharge in the farfield (approximately to 10-66 km) were measured using the deliberate tracer sulfur hexafluoride (SF6). The injection of SF6 was performed by bubbling the gas over a period of 6 days into an ocean outfall pipe discharging into the southeast Florida coastal ocean. The surface SF6 concentrations show that the discharged water flowed northward parallel to the coast with a broadening of the width of the plume to about 3 km at the farthest point sampled, 66 km from the outfall. The discharge was fully mixed throughout the water column within 13 km of the outfall terminus. In the first 20 km from the outfall, SF6 surface concentrations were highly variable, while beyond this the SF6 concentrations decreased monotonically going northward. The currents were measured during the study with a bottom-mounted acoustic Doppler current profiler (ADCP) located 5.5 km from the outfall. Velocities were variable in magnitude and direction but showed a net northward flow during the 6-day study. Maximum concentrations decreased by about 200-fold per kilometer from the outfall to the northern end of the study area. The study shows that SF6 is an effective method to trace point source releases far from their origin.

Initial dilution of submerged, single, round, buoyancy-dominated jets in a current is considered. Two simple semiempirical equations, one for centerline dilution and the other for minimum surface dilution, are presented. These equations are derived based on the continuity equation for the buoyant jet flow with a hypothesis that shear entrainment and forced entrainment can be added. Available laboratory and field data are used to determine the constants in the equations. Unlike asymptotic equations which apply for the limiting flow regimes, the proposed equations span all flow regimes, from the buoyancy-dominated near field (BDNF), to the transition, and to the buoyancy-dominated far field (BDFF), providing continuous predictions for dilutions.

Measurements of the underwater sound produced by rain were made at three U.S. coastal sites in a study to determine the feasibility and limitations of the acoustic detection and classification of rainfall over water. In the analysis of the rain sound spectra, concurrent radar reflectivity observations were used to identify convective and stratiform regions of the precipitating clouds overhead. It was found that acoustic classifications of rainfall as to type, based on information in the 4–30-kHz frequency band, were in general agreement with radar-derived classifications. The classification technique is based on use of an acoustic discriminant, DR, defined as the difference in average spectral levels between the 10–30- and 4–10-kHz bands. A high correlation was found between sound spectrum levels (in decibels) in the 4–10-kHz frequency band and radar reflectivity, dBZ, suggesting the possible use of the 4–10-kHz band sound spectral level as a classification tool using spatially distributed hydrop...

A methodology for ocean outfall mixing zone analysis is presented. It is based on a combination of four deterministic models for predicting hydrodynamic mixing behaviors of the discharged effluent, a continuous time domain simulation method, and an exceedance probability field concept. The approach provides a framework for evaluating mixing zones in compliance with receiving water criteria that are set in statistical terms. The approach was applied to the Hollywood outfall located off the east coast of South Florida. An exceedance probability field for effluent at a specified relative concentration of 0.021 was created. This field was applicable for determining the exceedance probability-based concentrations of any conservative pollutant at the regulatory mixing zone edge. A comparison of the probabilistic approach with the worst-case approach was made. The use of the worst-case approach was found to be too conservative for the subject outfall.

Automatic rain gauge systems are required to collect rainfall data at remote locations, especially oceanic sites where logistics prevent regular visits. Rainfall data from six different types of automatic rain gauge systems have been collected for a set of summertime subtropical rain events and for a set of wintertime rain events at Miami, Florida. The rain gauge systems include three types of collection gauges: weighing, capacitance, and tipping bucket; two gauges that inherently measure rainfall rate: optical scintillation and underwater acoustical inversion; and one gauge that detects individual raindrops: the disdrometer. All of these measurement techniques perform well; that is, they produce rainfall estimates that are highly correlated to one another. However, each method has limitations. The collection gauges are affected by flow irregularities between the catchment basin and the measurement chambers. This affects the accuracy of rainfall-rate measurements from these instruments, especiall...

Bottom surges generated from dredged material discharges in the open ocean have been observed using high frequency acoustic concentration profilers in several field studies during the past five years. the locations, water depths, bottom slopes, oceanographic conditions, and dredged material composition differed from study to study. Observed surges at three dredged material disposal sites may develop more than one surge peak for a single discharge. for water depths of the order of 10 m, surge height of the leading peak was estimated to be about one quarter of the water depth. for water of greater depth, of the order of 100 m, surge height reached 70 m, about 70% of the water depth. Surge height is established instantaneously when dredged material hits the bottom, and remains relatively constant as the surge advances horizontally. Total surge length reached 150 m for water depths of 10 m when measured from the impact point to the leading edge. for water depths of more than 100 m, the surge length r...

In February, 2007, a tracer study was conducted on the Boynton Inlet, Florida, using sulfur hexafluoride (SF 6 ) tracer. The objectives of this study were to determine if the data collected from the tracer study could be used to develop a farfield model of the plume exiting the Boynton Inlet using limited data to develop a useful predictive result. There are few studies of the farfield movement of inlet plumes in the coastal ocean. The plume was successfully modeled with a Gaussian plume model that appears to mimic the response. It was noted that the tracer concentrated in a series of boluses that migrated north of the inlet. Because the project injected the tracer for only 4 hours during the outgoing time, a long-term result that would hide the boluses was developed. The results showed velocities lower than predicted by the measured current data. The belief is that this is partially a result of tidal influences that affect outflow from the inlet.

Initial dilutions of four ocean outfalls (the Miami‐Central, Miami‐North, Hollywood, and Broward outfalls) on the east coast of South Florida were determined from dye and salinity studies. In the dye studies, continuous injections of the red dye Rhodamine‐WT into effluent were conducted; dye concentrations were measured using a deck‐mounted fluorometer with a ship‐towed sampler and from grab water samples. In the salinity studies, temperature and conductivity were measured using a towed conductivity‐temperature‐depth device (CTD); salinity deficit was taken as a tracer to determine initial dilution. Results show that initial dilutions determined from both methods are consistent. Data for initial dilution and for environmental and effluent parameters are interpreted using the dimensional analysis method. A comparison is made between the present data and data from previous studies. Data for Hollywood and Broward outfalls (single‐port discharges) are consistent with previous data. Data for Miami‐Central and ...

A field data collection project was undertaken to investigate the short-term fate of dredged material discharged in the designated Miami Ocean Dredged Material Disposal Site (ODMDS) before dredging of the Miami River and the Miami Harbor Turning Basin begins. the designated ODMDS is located in relatively deep water for discharge sites with a typical bottom depth of 150 metres and is also located in the western boundary region of the Gulf Stream current off Miami. Acoustical backscattering, current, particulate, temperature and salinity data were gathered over a three day period from April 24, 1990 through April 26, 1990. the major generic features of shallow-water discharge plumes were observed to be present: (a) the presence of a rapid convective descending plume portion; (b) impact of that plume portion with the ocean bottom and concomitant generation of a bottom surge; (c) rapid horizontal width growth of the descending plume through entrainment; and (d) retention of a residual plume portion w...

A study, called SEFLOE, of the dispersion characteristics of several wastewater outfalls was conducted off of the coast of Southeast Florida (USA). in this study, the feasibility of utilizing high frequency (20kHz and 200kHz) acoustic echoes to characterize the dilution characteristics of the effluent wastewater was examined. It is hypothesized that the background corrected acoustic backscattered intensity may be used to guide chemical/biological sampling, and that one or more plume subfields may be revealed by the scattering strength field. Data from SEAFLOE have indicated that the wastewater plume field is divided into regions of higher concentration spatially separated by regions of lower concentration; we call these regions of higher concentration “boluses”. When the water column is density stratified, subsurface plumes may peel off of the main rising plume and remain at equilibrium on a density gradient.

Pathways and dilution of a point source ocean discharge in the farfield (approximately to 10-66 km) were measured using the deliberate tracer sulfur hexafluoride (SF6). The injection of SF6 was performed by bubbling the gas over a period of 6 days into an ocean outfall pipe discharging into the southeast Florida coastal ocean. The surface SF6 concentrations show that the discharged water flowed northward parallel to the coast with a broadening of the width of the plume to about 3 km at the farthest point sampled, 66 km from the outfall. The discharge was fully mixed throughout the water column within 13 km of the outfall terminus. In the first 20 km from the outfall, SF6 surface concentrations were highly variable, while beyond this the SF6 concentrations decreased monotonically going northward. The currents were measured during the study with a bottom-mounted acoustic Doppler current profiler (ADCP) located 5.5 km from the outfall. Velocities were variable in magnitude and direction but showed a net northward flow during the 6-day study. Maximum concentrations decreased by about 200-fold per kilometer from the outfall to the northern end of the study area. The study shows that SF6 is an effective method to trace point source releases far from their origin.

To be protective of living marine resources the ocean disposal of dredged materials must be managed such that these activities do not significantly disrupt the natural environment upon which marine animal and plant communities depend. Two important controlling factors affecting the diversity, abundance and general health of hermatypic (stony) corals comprising reef communities in tropical and subtropical environments are sedimentation and the availability of sunlight for photosynthesis. Disposal activities result in residual sediment plumes which, when occurring near coral communities, can expose corals to increased suspended sediment levels and sedimentation rates and reduced light intensity. In order to avoid adverse impacts to corals, dredged material disposal guidelines should ensure that disposal activities do not add significantly to sedimentation and light attenuation caused by naturally occurring oceanographic and meteorological processes. The development of disposal guidelines requires an understanding of these processes and their influence on sedimentation and light availability. Studies of these processes are currently underway at the Miami, Florida Ocean Dredged material Disposal Site (ODMDS). Initial results of eight months of acoustical backscatter data collected from October 1998 to October 1999 suggest a marked seasonal difference in average natural background suspended sediment concentrations at reef locations inshore of the ODMDS. Fall seasonal averages were higher due in part to several hurricanes and tropical storms that caused high elevations of suspended sediments on reef communities for two to four day periods. Suspended sediment guidelines for dredged material disposal will depend on the importance of these major oceanographic and meteorological events as determining factors for coral reef structure and function.

Design of both real‐time studies of oceanic discharges of potential pollutants such as sewage effluent, and long‐term monitoring of same, are complicated by a number of factors. These factors include lack of knowledge of the space and time distribution of the discharge plume, proper placement sites for sample gathering, and lack of knowledge of the space‐time distribution of ‘‘interfering’’ plumes (plumes from sources other than the discharge plume under study). Progress has been made in the development of ‘‘integrated sensor suites’’ which produce data with substantial synergistic benefits. Ocean acoustics plays a key role in integrated sensor suite data unification. In a recent study in the coastal waters off San Juan, Puerto Rico, the ability of acoustics systems to view essentially the complete oceanic water enabled a connection to be made between salinity, temperature, and turbidity measurements gathered in the upper 5 m in the water column to a specific port of a sewage effluent diffuser. Having established the ‘‘connectivity’’ of the distal field measurement to a specific port, a dilution value at the distal point could confidently be calculated. This example is but one of many of the synergies available from utilization of multiple sensor suites unified through acoustics.

Natural systems such as lakes, rivers, and oceans can be described by dissolved and particulate components. Particulate sources in coastal oceanic environments include natural materials from seaward riverine and estuarine flows and anthropogenic sources such as ocean dumping and outfalls. Plumes of suspended particulate matter (SPM) can be natural (lithogenic and biogenic), anthropogenic, and any mixture of these. Because SPM can range from environmentally neutral (i.e., lithogenic and biogenic) to hazardous (heavy metals, bacteria,...), detecting, tracking, sampling, and sourcing SPM plumes can be beneficial for the environment and human health. Acoustic methods have proven successful in detecting and mapping oceanic SPM over large spatial areas but are limited in resolving internal fine structure, estimating relative contributions of merged plumes from various sources (e.g., river outflow versus dumping), and differentiating between introduced and in situ SPM. To complement acoustics, CTD/optical/water ...

Acoustical methods such as backscatter and Doppler current measurements are gaining substantial acceptance in both point source and nonpoint source oceanic pollution studies. Using acoustical backscattered energy, chemical and biological samplers are guided to oceanic water column regions of higher contaminant concentration. In typical discharge operations, e.g., dredged material, sewage effluents, oil‐well blowouts, after‐discharge backscatter levels are initially at least three to four orders of magnitude above normal background backscatter levels and are available for tracking of plumes and guidance of sampling operations. Additionally, acoustical backscatter may also be used to map naturally occurring surfaces within the oceanic water column along which both discharged material and naturally recurring particulates may accumulate. Thus nonacoustical sampling may continue to be guided indirectly far beyond the time or distance at which plume concentration levels may be considered to have diminished to a...

Outstanding features of the coastal ocean influencing the acoustical study of internal waves and turbulence include the large quantities of suspended particulates present therein and the regularity, both in characteristics and occurrence, of internal wave groups. The coastal ocean is often occupied by internal wave groups possessing a well‐known and consistent structure, namely, a set of amplitude‐ordered solitons followed by a sequence of quasilinear waves. Acoustical observations made using backscattered 20‐kHz pulses, of two events conjectured to be internal wave group‐generated mixing and resuspension events, will be presented. The first event occurs at the interface separating Hudson‐Raritan water from continental shelf water; the second event occurs in the ocean bottom boundary layer. A third event generated by an oceanic discharge of material event wherein simultaneous generation of internal waves, turbulence, and a midwater column “turbidity” particulate surge will also be presented. Some implicat...

Experimental data and theoretical calculations on the scattering of high-frequency acoustic signals from oceanic internal waves are presented. Acoustic data on internal waves are compared with simultaneous temperature (towed thermistor) data. The comparisons have shown a high degree of correspondence between the temperature and the acoustic data. Theoretical calculations for the acoustic scattering cross section σ are made by assuming that temperature fluctuations give rise to the acoustic scattering. An enhanced cross section for scattering from layered temperature fluctuations is to be expected, in agreement with the 1973 calculations of W. H. Munk and C. Garrett.

Surface manifestations of oceanic internal waves have been studied in Landsat-1 and -2 data since 1972. The internal waves appear as periodic, intermittent variations in the surface optical reflectivity and are visible from spacecraft, aircraft, and surface vehicles under certain circumstances. The Landsat data suggest that the source of the waves is semidiurnal and diurnal tidal action at the edge of the continental shelf. A study of the wave characteristics yields considerable insight into the physics of their excitation, propagation, and dissipation. Packets have been observed from the Gulf of Maine to Cape Hatteras and in images taken off the U.S. and African east and west coasts, the Gulf of Mexico and the Caribbean, The Gulf of California, the Sulu Sea, and the Baltic. The internal wave groups show an orderly variation in wavelength from front to rear of the packet, due to a combination of frequency dispersion and nonlinear amplitude effects. An oceanographic cruise was carried out in synchronism with two 18-day Landsat-1 cycles, and data were taken on temperature, density variations, acoustic echoes, and surface slicks accompanying the internal waves. The data were satisfactorily correlated with spacecraft and U-2 imagery taken simultaneously.

Acoustic observations of a low-density sediment flow originating from a dredge operating in the main Miami shipping channel have been made. The flow proceeded seaward along layered thermal gradients at the top of the shallow thermocline and at greater depths. Acoustic, thermal, salinity, chemical, and transmissivity measurements were made during summer and winter in 1974.

A method is derived for extracting oceanic dynamic height anomaly from collinear (exact repeat mission) GEOSAT short (∼ 1,000 km long) orbit segments. The procedure requires at least 1 year of simultaneous in situ observations and involves: (1) computing with respect to the ellipsoid, a mean sea surface height (SSH) profile solely from altimetry, (2) linear least‐squares removal of tilt and bias from individual SSH profiles with respect to the mean profile, (3) determining an independent mean dynamic height anomaly profile from hydrographic data along the orbit segment, (4) demeaning the tilt‐and‐bias removed individual SSH profiles and addition of the mean in situ dynamic height anomaly, and (5) correcting for concurrently observed dynamic height anomaly at two or more suborbital points during satellite transit. Analysis of the concept suggests root sum squared errors of ±5 cm, which can be reduced by smoothing and longer term measurements along the same orbit segment. A 1‐year comparison betwee...

Internal waves on the continental shelf off New York have been observed from ship and the ERTS-1 spacecraft, and positive correlations made between surface and subsurface measurements of temperature, acoustic volume reflectivity, and surface slicks. The spacecraft imagery senses the quasi-periodic variations in surface optical reflectivity induced by the internal waves. The waves appear to be tidally generated at the shelf edge and occur intermittently in packets, which propagate shoreward and disappear in water near 50-m depth.

An acoustic (3 MHz) backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer. Laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well-sorted fine to coarse quartz sands typical of those found in marine sediments. Departure of the calibration curves from their expected values is thought to be due to the non-spherical shape of the quartz grains. Field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles (taken at 1 Hz) during erosion events are characterized by highly variable concentrations. Surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25-100 cm above bottom. Averaging produces smooth profiles which fit well log-normal distributions predicted by steady flow suspended load theories.

Low density plasma-double gridded antenna system for ion and electron signal propagation studies, observing multiple reflections of acoustic and ballistic pulses and bulk phenomenon

Previous work on determining the acoustic cross section of sand grains [Geophys. Res. Lett. 9(2), 175–178 (1982)] identified a problem with the application of the simple compressible sphere model for the cross section. Use of the complete elastic sphere model [J. Acoust. Soc. Am. 34, 1582–1592 (1962)] failed to remove the conflict with observation. Application of the bistatic cross‐section theorem to the angle averaged cross section shows that the appropriate cross section is the total absorption cross section, not the backscatter cross section. The total absorption cross section for the fluid sphere model is found to be in semiquantitative agreement with scattering data for sand grains.

CLOUDS of suspended particulate matter in the ocean have been observed by satellite1, sensed by nephelometers2, and sampled by water bottles. We present here evidence that it may be possible to observe oceanic suspended particulate matter acoustically. The particulate matter discussed is thought to have arisen from a dredging operation. It is also thought that the suspended matter is present at lower concentrations than any in any other case recorded acoustically3. Certain questions, as yet unresolved, regarding acoustic scattering strengths are also discussed.

Spires or humps of particulate material extending from the bottom of the oceanic mixed layer to near the ocean's surface have been observed in the Florida Current and in the regions of other current systems, using an ultrasensitive, 20-kHz acoustical echo sounding system. These spires may be the result of oceanic circulation rather than a purely biological phenomenon.

Knowledge of the rate of dispersion of particulate matter dumped in the upper ocean and of the processes governing that dispersion is fundamental to an understanding of the effects of dumping on the ocean environment. Accurate chemical dilution rates of dumped material cannot be determined without a knowledge of the spacial distribution of ocean dumped material and the way in which that distribution changes with time. Acoustical methods offer one approach to studying ocean dispersion of dumped material. Acoustical results presented herein show some of the complicated effects which gradients in oceanic parameters, such as temperature and density, produce in the dispersion of particulate matter dumped in the ocean.

The possibility of extracting useful bottom information from reflected pulse waveforms at customary echo-sounding frequencies has been demonstrated experimentally. The one-dimensional nature of the sediment property continuum should also enable the use of remotely measured acoustical sedimentary properties to predict navigationally important mechanical characteristics.

The definition of 'Ocean Bottom' for charting and other purposes depends strongly on the nature of the system used to measure depth. The dominance of acoustic echo sounding suggests a definition directly in terms of acoustic echos. NOAA has undertaken a research program to improve echo sounder performance and to add remote sediment characterization capability. Details and results of this work are presented. A possible 'Standard Acoustic Bottom' based on this work is outlined.

With a modified 200-kilohertz acoustic echo sounder, it has been possible to detect and map sewage dumped into the ocean over several hours. The three-dimensional distribution of suspended material and its rate of diffusion are indicated after digital processing of the data.

Acoustical methods play an important role in the in the study of nutrient sources for coral reef ecosystems in the south Florida coastal ocean. Many nutrients released into the coastal ocean are released in distinct water masses such as inlet discharge plumes, wastewater outfall discharge plumes, and hurricane‐induced re‐suspensions. Using water column acoustic backscatter profiles, obtained via either ship‐borne instrumentation or in‐situ instrumentation, multidimensional images of nutrient bearing water masses are derived. Said images are of assistance in the design of chemical and biological sampling efforts. Examples of water mass imaging will be presented as well as the use of such images in the design of water quality sampling programs. Using a combination of acoustic backscatter, Doppler current profilers, nutrient (nitrate, nitrite, silica, phosphate, ammonia) samples and microbiological (fecal, protozoa, viruses) samples, flux estimates of said quantities may be made for inlet discharges. Results...

PULSED high frequency acoustics has been shown to have unique applications in the detection and measurement of oceanic phenomena such as internal waves1–3 and dispersion of ocean-dumped sewage sludge4,5 or dredge material6. With moderate to high pulse repetition rates, a virtually continuous record of water column scattering strength is available to depths of the order of 500 m from a ship travelling at speeds of 4 or 5 knots. We used this feature to detect acoustically the interfaces associated with an intrusion of cold New England shelf water into the warmer slope water during a 9-d period in June 1976.

Narrow beam echo sounders were used to characterize the spatial distribution of wastewater plume material from six ocean outfalls in the South Florida area. Volume scattering strengths were computed and plotted as a function of depth and horizontal distance for 200‐kHz echoes. Reduction in peak scattering strength with increased range from the outfall locations correlated well with reduction in concentration of Rhodamine‐WT dye introduced into the undiluted wastewater at a concentration of 1 ppm. Sound power reflection coefficients ranging from 10−5 to 10−9 were observed for these wastewater plumes. The data presented demonstrate the degree to which the sound power reflection coefficient for a distribution of scatterers is dependent upon the concentration of those scatterers, and show the utility of the acoustical method in water‐mass characterization.

A bottom‐mounted 200‐kHz narrow beam coherent acoustic Doppler system was used to observe profiles of vertical water velocity in Chesapeake Bay (17‐m water depth) near the mouth of the Patuxent river in August 1982. Internal wave induced vertical water motion was up to 2 m as shown by observation of biological scattering layers. Coherent Doppler measurements gave vertical water velocities of several centimeters per second. The scattering layer motion and the velocity were in phase quadrature and the amplitudes were consistent with propagating internal waves. Of several types of internal waves seen, the most common were simple interfacial waves on the pycnocline, but some instances of higher mode waves were observed: Soliton wave packets were also seen. Problems of signal processing and of removing the aliasing resulting from the use of pulse‐to‐pulse coherent Doppler processing are also discussed. Fairly simple modifications to standard scientific echo sounders make it possible to extract vertical velocit...

The possibility of using a dynamical‐model‐based equatorial ocean data assimilation technique as the basis for tomographic inversion is explored. In the equatorial Pacific relatively few ray paths come near the surface causing difficulty for most inversion techniques. A data assimilation technique being developed at the Physical Oceanography Division of AOML/NOAA [Thacker and Long, in preparation] uses a dynamical approach that can provide coupling between the deep conditions that are directly sensed by the acoustics, and the near surface events that are of direct climatic significance. The model decomposes temperature variability into dynamical modes identifiable with Kelvin and Rossby waves; the sensitivity of individual ray‐path travel times to the modes is used as the basis for the inversion. The acoustic data is assimilated with other ocean measurements by using a LaGrange multiplier approach constrained by the dynamics. Ray tracing results using equatorial Pacific temperature data are presented whic...

Landsat imagery taken over the Sulu Sea, Philippines, reveals the existence of very long, soliton‐like internal wave pockets of semi‐diurnal periods. An experiment was conducted in May 1980 to test the hypothesis of tidal generation, and to parameterize these soliton waves by obtaining additional measurements using acoustic remote sensing techniques as well as conventional methods. In this paper, we compare wave characteristics from various measurements, and present different wave forms due to ship speed change with respect to the wave velocity. Effects of deep scattering layer on the acoustic measurements are discussed, using computer‐digitized backscattering intensity contour.

The question of accurate measurements of chemical or toxicant dilution rates in the ocean continues to be of fundamental interest to both the research and coastal management communities in the U.S. Results will be presented on the use of acoustical data to guide chemical sampling and reinforce chemical data on dilution rate estimates. Acoustical data will be presented which indicates the basic spatial variability scales of concentration of material dumped in the ocean for certain sites; the attendant implications for the statistical reliability of associated chemical data will be discussed.

Acoustic bottom echoes at frequencies from 10 to 380 kHz were recorded for a variety of bottom types in southern Chesapeake Bay. Short pulse lengths and direct digital recording allowed temporal resolution of 100μs to be achieved. Supporting measurements of sediment characteristics and bottom roughness allowed comparison of the measurements with theory. The field observations were in good agreement with the theory after corrections for the interaction of transducer beam patterns with bottom roughness were made.

Studies have been carried out on the oceanic bottom boundary layer using 20 kHz and 3 MHz sound systems. Data will be presented on the generation of a suspended layer of sediment, essentially confined within the bottom boundary layer, by nonlinear internal wave groups on the N.Y. Continental shelf in 120 m of water. Data will also be presented on the existence of a large underwater “cloud” of material found on the continental slope (water depth typically (600‐300 m) which has been observed consistently over the last several years and which is highly acoustically reflective. Some data from a high resolution (≃ 1 cm) 3 mHz‐acoustical system on particulate concentration estimation will be presented.

An approach to monitor drilling fluid discharge from an oil rig and to map its plume distribution by high‐frequency acoustics was proposed. Experiments were conducted at two nearby rigs of the East Flower Garden Bank in the Gulf of Mexico, and data were used to provide vertical plume structure and two‐dimensional distribution maps at fixed depth. The ability to monitor the discharged plume continuously in time and space makes the acoustic technique more convenient and cost effective than other conventional methods.