ALBERT

Description: This report describes the design and capabilities of a new ocean bottom hydrophone instrument. The instrument is microprocessor controlled and records digitally on a commercially available cartridge tape recorder with a formatted capacity of 16.7 megabytes. It can operate at sampling intervals between 80 and 8500 Hz and has a dynamic range of 120dB. Both the hardware and software are designed to provide the maximum flexibility in operation allowing either preprogrammed or event detect operation for either short deployment high sampling rate experiments or extended deployment low data rate applications. The microprocessor and recording electronics are capable of handling four data channels and thus the existing recording package is suitable for the ocean bottom seismometer application (or similar} with little or no modification.

Description: Prepared for the Office of Naval Research under Contract N00014-82-C-0019; NR 083-004.

Description: This report describes the development of a facility for recording time-varying computer graphics on video tape. The primary purpose of the facility is to produce animation sequences of ocean and seafloor acoustic wave fields from output of the synthetic seismogram numerical model FINDIF, and to record them on convenient portable VHS video tapes. The facility utilizes a suite of computer programs called AFRAME, and an Abekas model A60 digital video disk which is connected to the modeling computer and to broadcast quality video recording equipment.

Description: This work was carried out under ONR Grant #N00014-90-J-1493

Description: A study was carried out to quantify the level of numerical noise in numerical scattering chamber (NSC) calculations and to compare these noise levels with signal levels of body waves, interface waves and ambient noise. The amplitudes of signal and noise in snapshots from the numerical scattering chamber were quantified at 50 and 65 periods for a few reference models. Models with homogeneous subseafloor structure were studied to determine the level of numerical noise; models with a wavenumber-correlation length product of one were examined to determine signal levels. Models were run with both Higdon and telegraph equation absorbing boundaries since the numerical noise within the grid depends on the boundary formulation. Amplitudes were measured along data traces obtained at a grid depth of 3.33 λw and at the seafloor. Forward traveling head waves had typical amplitudes of ±125 but may reached ±250 near the direct wave. Diffraction amplitudes were observed up to ±300. Stoneley wave amplitudes ranged from ±800 up to ±20,000. Numerical noise levels were less than ±25 in most areas of the water and less than ±350 along most of the seafloor. Regardless of the absorbing boundary type, however, there was a region of noise extending up to 15 λw behind the first seafloor reflection at 3.33 λw in which noise levels range from ±100 up to ±600. In this region it is difficult to resolve signal from systematic numerical noise.

Description: This work was carried out under ONR Grant #N00014-90-J-1493

Description: The Ocean Bottom Seismometer Augmentation in the North Pacific Experiment (OBSANP, June-July, 2013, R/V Melville) addresses the coherence and depth dependence of deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we observed "deep seafloor arrivals" (DSFA) that were dominant on the seafloor Ocean Bottom Seismometer (OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line Array (DVLA) (above 4250m depth). At least a subset of these arrivals correspond to bottomdiffracted surface-reflected (BDSR) paths from an out-of-plane seamount. BDSR arrivals are present throughout the water column, but at depths above the conjugate depth are obscured by ambient noise and PE predicted arrivals. On the 2004 NPAL/LOAPEX experiment BDSR paths yielded the largest amplitude seafloor arrivals for ranges from 500 to 3200km. The OBSANP experiment tests the hypothesis that BDSR paths contribute to the arrival structure on the deep seafloor even at short ranges (from near zero to 4-1/2CZ). The OBSANP cruise had three major research goals: a) identification and analysis of DSFA and BDSR arrivals occurring at short (1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03 to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths. On OBSANP we deployed a 32 element VLA from 12 to 1000m above the seafloor, eight short-period OBSs and four long-period OBSs and carried out a 15day transmission program using a J15-3 acoustic source.

Description: Funding was provided by the Office of Naval Research under contract #'s N00014-10-1-0987 and N00014-10-1-0510

Description: A sequence of nine nighttime, broadband volume scattering strength measurements obtained in 1973 over a period of approximately one hour was used to study the short-term variability of scattering strength in 100 Hz bands over frequencies ranging from 100 Hz to 24 kHz and depths ranging from 400 meters to 1000 meters. The variability was found to be independent of depth and was least in the frequency range three kHz to eight kHz where the standard deviation was approximately four dB less than the mean level, Outside this frequency range the standard deviation was somewhat greater than the mean level.

Description: This work was funded by the Naval Underwater Systems Center, Commercial Acquisition Dept., Building 11, Code 09, Newport, Rhode Island 02841-5047 under contract number N00140-85-C-JA45.

Description: This is the final report of Contract N00014-84-C-0185 between the Woods Hole Oceanographic Institution and the Office of Naval Research for the contract period 1 January, 1984, to 28 February, 1985. This contract supported an experiment that was conducted in the Norwegian Sea during May and June of 1984 to assess the possibilities of using ocean acoustic tomography as a measuring tool in the Arctic. The object of the experiment was to identify and determine the temporal stability (coherence), and resolvability, of Arctic acoustic paths. Identification refers to the ability to match a pulse arrival with a particular ray path, primarily through computer modelling. Resolvable rays are those that arrive sufficiently far apart in time so as to be distinct and separable. In order to use tomography, rays must be identified, resolved and stable. Unlike the deep temperate ocean, where there are many wholly refracted paths, the upward refracting Arctic sound speed profile causes ray paths to reflect off the ice-covered surface of the permanent pack and the mixed ice-covered and ice-free surface of the marginal ice zones. The reflection process is time-varying and hence leads to resolvability, identification and stability questions that do not arise in the case of entirely refracted paths. A 224 Hz acoustic source was moored in an ice-free region. It transmitted phase coded, frequency stable signals to receivers fixed on the bottom and receivers drifting with the icepack at ranges of approximately 150 km. The received signals are to be analyzed with respect to identification, resolvability and stability issues. This contract covered the costs associated with installation and retrieval of the source and preliminary data reduction from the drifting and fixed hydrophones. Detailed data analysis costs are to be covered elsewhere. Nevertheless, preliminary analysis indicates that the received signals, particularly those from paths that interact with the ice-free surface, appear to have sufficient stability for tomographic purposes.

Description: Funding was provided by the Office of Naval Research under Contract N00014-84-C-0185.

Description: The work sponsored by ARPA at Woods Hole Oceanographic Institution is having an impact on efforts by those not directly involved in the projects both within and without the Institution. The navigation system being developed for submersible/mother ship has been recognized as a very useful system by members of the Geology/Geophysics Department and the Department of Physical Oceanography. Each department is now developing their own system based on the work already completed by the Ocean Engineering Department under the ARPA contact. Through the ARPA contract ComPhibLant (specifically ComPhibRonTen) was shown some of the advantages of doing something new about small boat and heavy object handling at sea and this program is expected to have some direct effect upon methods they will use in the future. Although the project concerned with developing biological equipment for deep sea work has not continued as part of the ARPA program, the seed was succssfully sown and several items are being developed at the Institution under separate funding. All the projects continued at a fair pace but not without some problems. The Deep Sea Rock Drill had some minor setbacks during operations with ALVIN, and the Air-Sea System (Long Range Ech-Ranging) project was hampered by a faulty engine aboard the air craft. Summaries of progress are given immediately below and more detail is available in the individual reports further on.

Description: Prepared for the Office of Naval Research under Contract N00014-71-C00284; NR 293-008.

Description: High frequency acoustic backscattering systems are being used in monostatic modes to evaluate the use of acoustic techniques to detect and study a variety of fluid processes in the oceanic environment. A short outline of those research programs actively evaluating and using acoustic techniques is presented, followed by a detailed review of this investigator's program. This program uses a multifrequency high frequency acoustic system to study a variety of processes including turbulent mixing, air-sea interactions, internal waves, interleaving water masses, natural particulate dispersion and distribution, the dispersion of particulates associated with deep ocean disposal of industrial chemical waste, and biological response to a variety of stimulae including fluid motion, predators, and oceanographic instrumentation. Graphic acoustic data records of several of the above phenomena are described.

Description: Prepared for the Office of Naval Research under Contract N00014-77-C-0196; NR 083-004, for the National Oceanic & Atmospheric Administration under Grants NA79AA-D-00030 (Ocean Dumping Program) and NA79AA-D-00102 (Office of Sea Grant) and for the National Science Foundation under Grant OCE 77-08682.

Description: Originally issued as Reference No. 66-10, series later renamed WHOI-

Description: It is suggested in this report that the intensity of midwater sound-scattering in the ocean varies from point to point as the abundance of marine life varies. Several charts depicting variations in the abundance of marine life are given, from which estimates of the intensity of sound-scattering can be made.

Description: Submitted to the Offiae of Naval Researah under Contraat Nonr-4029(00JNR 260-101.

Description: Also published as: Journal of the Acoustical Society of America 68 (1980): 1750-1767

Description: Acoustical signals at 270 Hz from SOFAR floats drifting in the region southeast of the Gulf Stream were recorded during most of 1975 from a near axis sound channel hydrophone near Bermuda. The amplitude levels received exhibit a large increase (12–18 dB) commencing about 24 July, following a long period (March to July) of relatively lower peak level amplitudes. A major part of the increase can be attributed to the influence of a large cyclonic eddy (Gulf Stream ring) that passed slowly between the SOFAR floats and Bermuda. Such an eddy produces a large sound speed anomaly that extends to depths below the axis of the sound channel. On 24 July, two SOFAR floats were known to have approximately the same sound transmission path through the edge of the large eddy. The sound transmission peaks occur when no ocean eddy is between the SOFAR floats and the receiver. Their spacing shows they occur at regular refraction caustics in the sound channel. When the sound transmission path passes through an eddy, these transmission focal distances are shifted to greater range and the signal level may be greatly enhanced. The decrease of caustic peak intensities with range is 5 dB per double distance, and this agrees with theory. Several different levels of peak acoustic intensity occur and these result from two float depths and oceanic thermocline oscillations.

Description: Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004·.

Description: Also published as: Journal of the Acoustical Society of America 69 (1981): 982-988

Description: A phase-coded signal with 64-ms resolution was transmitted at 10-min intervals for a 19-day period over two ~300-km ranges. The acoustic source was moored at 2000-m depth northwest of Bermuda. One receiver was moored at 2000-m depth to the northeast of the source and the other receiver was bottom mounted at ~1000- m depth near Bermuda. The large (~0.6 s) travel time change at the Bermuda receiver is probably due in large part to motion of the source mooring in the presence of currents. The multipath arrival pattern at the moored receiver undergoes significant modification due to the presence of a southern meander of the Gulf Stream which intersects this transmission path.

Description: Prepared for the Office of Naval Research under Contract N00014-77-C-0196 and NORDA contract N00014-79-C-0071.

Description: The system described provides wide operational flexibility at any operating frequency from 5 kHz to over 800 kHz (except for a small band around 455 kHz) limited mainly by the availability of transducers. Variable pulse width, variable receiver bandwidth, low receiver noise, various time variable gain functions and wide system dynamic range characterized the system. Built-in time-sharing controls maximize flexibility of graphics display on either dry-paper or fibre-optic CRT recorders.

Description: Prepared for the NORDA under Contract N00014-77-C-0196; and for the National Oceanic and Atmospheric Administration under Grant 04-8-MO1-43.

Description: Also published as Journal of Geophysical Research, Vol. 83, No. C8, 1978, pp. 4062-4068

Description: Acoustic data, transmissometer data, and calculations are presented which indicate that high-frequency acoustic backscattering systems can become a valuable tool in the remote monitoring of suspended particle distributions and active resuspension areas. Data are also presented which show that acoustic backscattering systems can be used to remotely detect slope/shelf water frontal zones. Towed acoustic systems should be able to map the extent of the frontal zone and add significantly to the understanding of frontal zone processes.

Description: Prepared for the Naval Oceanic Research and Development Activity under Contract N00014-77-C-0196.

Description: Also published as: Journal of Geophysical Research 85 (1980): 3759-3777

Description: A detailed seismic refraction experiment was carried out across the Kane Fracture Zone near 24°N, 44°W using explosive and air gun sound sources and eight ocean bottom hydrophone receivers. The shooting lines and receive rs formed a 'T' configuration across the fracture zone, with two receivers located about SO km apart in the fracture zone trough and the remaining six receivers positioned 25-30 km apart on either side of the fracture zone. The crustal thicknesses and velocities observed at the receivers located north and south of the Kane Fracture Zone fall within the range of those typically observed for normal oceanic crust. There is no convincing evidence for signficantly different crustal thicknesses or upper mantle velocities on either side of the fracture zone despite a 10-m.y. age difference. Anomalously thin crust is present beneath the Kane Fracture Zone trough with total crustal thicknesses of only 2-3 km, about half the thickness of normal oceanic crust. This crust is also characterized seismically by low compressional wave velocities (~4.0 km/s) at shallow depths and the absence of a normal layer 3 refractor. This anomalous crust extends over a width of a t least 10 km. Dense, high-velocity mantle type material may also exist at shallow depths beneath the adjacent Kane Fracture Zone ridge. Results from other geological and geophysical studies of fracture zones suggest that this type of crustal structure may by typical of many Atlantic fracture zones. We propose that the anomalously thin crust found within these fracture zones is a primary feature caused by the accretion of a thinner volcanic and plutonic layer within the fracture zone. This anomalous crust, which probably is restricted to a zone no wider than a typical transform fault valley (~10 km) in most cases, is inferred to consist of a few hundred meters of extrusive basalts and dikes overlying about 2 km of gabbro and metagabbro, possibly interbedded with ultramafics. This anomalously thin crustal section may be extensively fractured and brecciated at shallow levels by faulting in the active transform domain. A relatively narrow zone of thin crust within fracture zones can ex plain a number of geological and geophysical characteristics of fracture zones including the depth of the transform fault valley and the exposure of deep crustal and upper mantle rocks in the walls of fracture zones.

Description: Prepared for the Office of Naval Research under Contract N00014-74-C0262 NR083-004.

Description: During July and August of 1980 near surface water velocities of Lake Huron were measured by tracking drogues, equipped with sonobuoys, using an acoustic travel time technique. Prior to these experiments difficulties associated with acoustic ray bending in the shallow, highly stratified environment were anticipated. Simple models were developed to predict the errors in drogue position and velocity determination resulting from ray bending. During the experiments round trip travel times of acoustic pulses transmitted between three bottom transponders and a transducer (lowered from a ship) were recorded. These combined with ray diagrams strongly suggested that, for a separation between the transducer and a bottom transponder of about 1.2 km, pulses which were detected first traveled by two paths, that of an inflected ray and that of a ray trapped beneath the thermocline. The error in position and velocity determination associated with these paths was 1 to 2%. Evidence also indicated that increased thermocline depth resulted in decreased tracking range.

Description: Prepared for the Department of Energy under Contract DE-AC02-79EV10005 and for NOAA under Contract 03-5-022-26.

Description: Also published as: Journal of the Acoustical Society of America 68 (1980): 1376-1390

Description: Seventeen piston cores up to 13 m long were recovered from representative acoustic and lithologic environments of the Hatteras and Nares Abyssal Plains in the western North Atlantic. Compressional-wave velocities (corrected to in situ conditions) and bulk physical properties measured on the cores are used to characterize the acoustic framework of these areas. For correlation with conventional seismic data, wholecore averages of properties are a better index to the acoustic nature of abyssal plain sediments than properties of the upper few centimeters of the seafloor because (I) strong changes in lithofacies (and acoustic properties) occur over depth scales of tens of centimeters to meters in the sediment column, and (2) conventional seismic frequencies of 3.5 kHz or less sample these variations to subbottom depths of tens of meters and more. Wholecore properties are a function of the thickness and distribution of high-velocity silt and sand layers in the core; they vary in a complex fashion with proximity to the source of turbidity currents, distance from axial paths of turbidity-current flows, local and regional basin geometry, and seafloor slope. Thus strongly reflective seabed regions with numerous high-velocity layers are not restricted simply to near-source areas nor are weakly reflective seabed regions (clay sediments only) limited to "distal" areas. Whole-core properties show a good qualitative correlation to variations in 3.5-kHz reflection profiles, and 3.5-kHz echo character therefore provides a useful means of mapping general acoustic properties over large regions of abyssal plains.

Description: Prepared for the Office of Naval Research under Contracts N00014-75-C-0210 and N00014-79-C-0071; NR 083-004.

Description: Also published in: Proceedings of the 8th International Colloquium on Ocean Hydrodynamics

Description: The techniques of flow measurement which have been successful in laboratory studies of boundary layer turbulence are difficult to use in the ocean; and the current meters penerally used in the ocean are not suited to measuring bottom boundary layer flow . A suitable sensor for bottom turbulence measurements should measure vector components, respond linearly to these components, maintain an accurate zero point, disturb the flow negligibly or in a well predicted way, and sense a small enough volume to represent the important scales of the flow. We have constructed an acoustic travel time sensor in a configuration that will allow vector components of the flow to be measured with sufficient accuracy to compute Reynolds stress at a point 50 cm above the bottom. This sensor responds linearly to horizontal and vertical flows in flume tests. When the flow is neither horizontal nor vertical, the wake from one acoustic transducer may interfere with the measurement along one sensing path but there is sufficient redundancy in the determination to reject this path and still resolve the vector velocity. An instrument· using four of these sensors is being designed to measure Reynolds stress in the lower six meters of the ocean.

Description: Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004.

Description: Formulas for curve fitting and ray computation using compound models made up of several different layers are presented. Examples of computation by pocket programmable calculator on two Sargasso Sea profiles, one from the center of a cold ring eddy are given. Necessary tables of the incomplete beta-function and calculator programs are included in a supplement.

Description: Prepared for the Office of Naval Research under Contract N00014-77-C-0196.

Description: The Mid-Ocean Dynamics Experiment (MODE) under the Office of the International Decade of Oceanography, National Science Foundation, included plans for the deployment of long-range SOFAR floats in a two degree square area approximately 400 miles Southwest of Bermuda. The floats are located by AFETR, MILS system hydrophones at Bermuda, Eleuthera and Puerto Rico. An additional station at Grand Turk Island, British West Indies, was requested to provide an expanded and more reliable location. In addition a spare installation was to be provided which could be installed within relatively short notice at Eleuthera or Puerto Rico if required. The design, logistical considerations and installation of the Grand Turk Island station are documented in this report.

Description: Prepared for the National Science Foundation under Grant GX-32571.

Description: This is the final report of Contract N00014-77-C-0196 between the Woods Hole Oceanographic Institution and the Office of Naval Research for the contract period l January 1977 to 28 February 1983. This contract supported a broad program of research and development in underwater acoustics related to present and future Navy systems and requirements. The bulk of this contract research was conducted from 1977 to 1981, during which time the categories outlined below were all areas of active research. (Between 1981 and 1983 the contract remained in effect, although only in the area of bottom acoustics and at a reduced level.) The primary contract products are the published technical reports and papers listed below. These reports give detailed descriptions of the research work and the specialized techniques, methods, and instrumentation developed to support this research program. The final report contains a brief review of the program highlights and a bibliography of associated reports.

Description: Funding was provided by the Office of Naval Research under Contract N00014-77-C-0196.