Christopher D. Jones

Underwater acoustic communication by passive-phase conjugation: theory and experimental results

A new method for coherent underwater acoustic communication called passive phase conjugation is evaluated. The method is so named because of conceptual similarities to active phase conjugation methods that have been demonstrated in the ocean. In contrast to active techniques, however, the array in passive phase conjugation needs only receive. The procedure begins with a source transmitting a single probe pulse. After waiting for the multipathed arrivals to clear, the source then transmits the data stream. At each element in the distant receiving array, the received probe is cross-correlated with the received data stream. This cross-correlation is done in parallel at each array element and the results are summed across the array to achieve the final communication signal suitable for demodulation. As the ocean changes, it becomes necessary to break up the data stream and insert new probe pulses. Results from an experiment conducted in Puget Sound near Seattle are reported. Measurements were made at multiple ranges and water depths in range-dependent environments.

Survey studies hydrothermal circulation on the Northern Juan de Fuca Ridge

The circulation of hydrothermal fluid within upper oceanic crust constrains the global composition of seawater and is also responsible for many of the dynamic chemical and biological processes that alter the underlying volcanic rocks that form the sea floor. The heat of crustal formation drives this fluid circulation, and the impact on the overlying ocean is most easily observed at mid-ocean ridge spreading centers. Previous efforts to quantify the heat associated with crustal formation have lacked information regarding the partitioning of thermal energy between discrete, high-temperature vent fields, ubiquitous low-temperature diffuse venting, and the pervasive conductive heat flux through the volcanic rocks.

Acoustic imaging, visualization, and quantification of buoyant hydrothermal plumes in the Ocean

We develop and apply visualization and quantification methods to reconstruct hydrothermal plumes in 3D from acoustic images and to make the first direct measurements from the reconstructions of scalar properties that describe the behavior of two buoyant plumes discharging from adjacent black smoker chimneys. The actual behavior is then compared to that predicted by a classic simple buoyant plume model. The images are reconstructed as isointensity surfaces of backscatter from particulate matter suspended in the plumes. The measurements pertinent to the role of the plumes as agents of dispersal of heat and mass into the ocean include change with height of diameter, particle distribution, dilution, centerline attitude, surface protrusions, and connectivity. The protrusions are the surface expression of eddies and appear to follow a bifurcating helical flow pattern that resemble simulation of the naturally forced flow of coherent vortex rings as the eddies rise with the buoyant plume. These direct measurements and the derived entrainment coefficient are generally consistent with behavior predicted by the simple buoyant plume model and support engulfment by vortex shedding as a primary mechanism for entrainment of surrounding seawater. Deviations from predicted buoyant plume behavior are diagnostic of particle dynamics.

Fine-scale sedimentary structure: implications for acoustic remote sensing

Abstract Detailed measurements of sediment properties and acoustic scattering were made at a carbonate sand–silt–clay site off Dry Tortugas in the Florida Keys. The sediment is characterized by varying scales of biologically controlled random roughness and heterogeneity as well as surficial stratification on centimeter scales. The interface roughness was determined from stereo photogrammetric digitization and parameterized by a power spectrum, whereas sediment volume heterogeneity was determined from core measurements and parameterized by first-order autoregressive models for sound speed and density fluctuations. In contrast to previous investigations, fine-scale sediment bulk density fluctuations were examined in sediment cores with computerized tomography in addition to the standard gravimetric technique. Furthermore, the strongly delineated sediment density and sound velocity transition layer was parameterized by piecewise linear fits. These characterizations of the random and deterministic properties were used in acoustic scattering models in an effort to determine the feasibility of remotely measuring fine-scale features of the seafloor. The result was negative: older, low-resolution models gave moderately good fits to the acoustic data, but the fit did not improve for newer, higher-resolution models. It is suggested that scattering due to shell fragments must be included to account for all features observed in the scattering data at this site.

Acoustics advances study of sea floor hydrothermal flow

Sub-sea floor hydrothermal convection systems discharge as plumes from point sources and as seepage from the ocean bottom. The plumes originate as clear, 150–400°C solutions that vent from mineralized chimneys; precipitate dissolved metals as particles to form black or white smokers as they turbulently mix with ambient seawater; and buoyantly rise hundreds of meters to a level of neutral density where they spread laterally. The seepage discharges from networks of fractures at the rock-water interface as clear, diffuse flow, with lower temperatures, metal contents, and buoyancy than the smokers. The diffuse flow may be entrained upward into plumes, or laterally by prevailing currents in discrete layers within tens of meters of the sea floor. The role of these flow regimes in dispersing heat, chemicals, and biological material into the ocean from sub-sea floor hydrothermal convection systems is being studied on a global scale.

Tracking beaked whales with a passive acoustic profiler float.

Acoustic methods are frequently used to monitor endangered marine mammal species. Advantages of acoustic methods over visual ones include the ability to detect submerged animals, to work at night, and to work in any weather conditions. A relatively inexpensive and easy-to-use acoustic float, the QUEphone, was developed by converting a commercially available profiler float to a mobile platform, adding acoustic capability, and installing the ERMA cetacean click detection algorithm of Klinck and Mellinger [(2011). J. Acoust. Soc. Am. 129(4), 1807-1812] running on a high-power DSP. The QUEphone was tested at detecting Blainvilles beaked whales at the Atlantic Undersea Test and Evaluation Center (AUTEC), a Navy acoustic test range in the Bahamas, in June 2010. Beaked whale were present at AUTEC, and the performance of the QUEphone was compared with the Navys Marine Mammal Monitoring on Navy Ranges (M3R) system. The field tests provided data useful to evaluate the QUEphones operational capability as a tool to detect beaked whales and report their presence in near-real time. The range tests demonstrated that the QUEphones beaked whale detections were comparable to that of M3Rs, and that the float is effective at detecting beaked whales.

Acoustic Observation of the Time Dependence of the Roughness of Sandy Seafloors

A statistical model for the time evolution of seafloor roughness due to biological activity is applied to photographic and acoustic data. In this model, the function describing small scale seafloor topography obeys a time-evolution equation with a random forcing term that creates roughness and a diffusion term that degrades roughness. When compared to acoustic data from the 1999 and 2004 Sediment Acoustics Experiments (SAX99 and SAX04), the model yields diffusivities in the range from 3.5 times 10-11 to 2.5 times 10-10 m2 s-1 (from 10 to 80 cm2 yr-1), with the larger values occurring at sites where bottom-feeding fish were active. While the experimental results lend support to the model, a more focused experimental and simulation effort is required to test several assumptions intrinsic to the model.

Underwater acoustic communication using passive phase conjugation

A new method for underwater acoustic communication called passive phase conjugation is evaluated. The method begins with a source transmitting a single probe pulse. After waiting for the multipathed arrivals to clear, the source then transmits the data stream. At each element in the distant receiving array, the received probe is cross-correlated with the received data stream. This cross-correlation is done in parallel at each array element and the results are summed across the array to achieve the final communication signal suitable for demodulation. The parallel processing makes the method computationally efficient and allows near real-time communication.

Water‐column measurements of hydrothermal vent flow and particulate concentration using multibeam sonar

High‐frequency multibeam systems enable water‐column studies of fluid flow from deep ocean hydrothermal vent systems. Backscatter from high‐temperature particulate‐laden vent fluid (black smokers) is used to obtain three‐dimensional images of the plume’s temporal and spatial structure. Backscattering intensity may provide a means to remotely estimate plume particulate concentration and turbulent micro‐structure created by temperature and density fluctuations in the plume fluid, providing denser sampling in space and time than conventional point measurements. Acoustic Doppler measurements can provide estimates of the entrainment and transport of water, particulate matter, and larvae by hydrothermal systems, which is of interest in physical, chemical, and biological oceanography. Toward the goal of providing an acoustic means of inverting for such oceanographic parameters with a multibeam system, several mechanisms and models of volume scattering from the water column will be discussed. The results from fie...

Overview: Civil-Military Relations in Central and Eastern Europe in Former Communist Societies

This article reviews studies on civil-military relations by David Betz (Russia), Daniel Nelson (Romania and Bulgaria), Natalie Mychajlysyn (Ukraine), Marybeth Ulrich (Czech Republic), and Mark Yaniszewski (Poland and Hungary). All note minimal progress in developing a cadre of civilian defense experts who can end the monopoly of ministries of defense on policymaking. Those states that are candidates for NATO membership have made much more drastic cuts in the size of paramilitary and internal security forces than have Russia and Ukraine. They have also moved toward postures and doctrines based on coalition security policies, which have all but ruled out the internal use of armed force on the model that Milosevic developed in the former Yugoslavia and Tudjman attempted to develop in Croatia. In Russia and Ukraine, the strong presidential systems have at their disposal large internal armed forces that could be available for targeting domestic political opponents or minority groups.