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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...

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...

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.

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...

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.

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.

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.

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.

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.

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.

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.