John R. Proni

On the use of high‐frequency acoustics for the study of internal waves and microstructure

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.

A study of oceanic internal waves using satellite imagery and ship data

Abstract 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 tracking of ocean-dumped sewage sludge.

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.

Farfield Tracing of a Point Source Discharge Plume in the Coastal Ocean Using Sulfur Hexafluoride

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.

On the use of acoustics for studying suspended oceanic sediment and for determining the onset of the shallow thermocline

Abstract 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.

DISPERSION OF PARTICULATES IN THE OCEAN STUDIED ACOUSTICALLY: THE IMPORTANCE OF GRADIENT SURFACES IN THE OCEAN

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.

Dredged Material Disposal at the Edge of the Florida Current

Abstract 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 simple model for the acoustic cross section of sand grains

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.

Acoustical observations of anthropogenic discharge plumes

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...

Acoustic methods for water mass delineation in coastal marine ecosystems

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...