Dr. John Jones, FIET

Abstract
Accurate in-situ studies of the oceans requires an efficient, fast and reliable method of transmitting information to and from dedicated scientific payloads. The current generation of underwater telemetry systems tend to use proven, low data rate, `discrete-component' designs. Although these systems perform well in static environments, their performance rapidly degenerates when the environment becomes more dynamic. The next generation of underwater telemetry systems must be able to… Show more

Abstract
Accurate in-situ studies of the oceans requires an efficient, fast and reliable method of transmitting information to and from dedicated scientific payloads. The current generation of underwater telemetry systems tend to use proven, low data rate, `discrete-component' designs. Although these systems perform well in static environments, their performance rapidly degenerates when the environment becomes more dynamic. The next generation of underwater telemetry systems must be able to adapt automatically to the changing environment and counteract time-varying effects by means of flexible signal processing techniques and detection algorithms. This goal is hard, if not impossible, to realise using conventional `discrete component' designs. This paper presents a vertical communication system that uses an `Analogue Devices' digital signal processor (DSP) at its heart. This DSP controls the transmission of data and operative commands to and from a seafloor unit, using multi-phase, 2, 4 or 8, differential phase shift keying (DPSK). This system is considered to be the first step towards a completely autonomous, adaptive communications system Show less

Abstract
VERTLINK is an acoustic telemetry link designed for oceanographic data collection in water depths up to 1km. It uses digital signal processor (DSP)-based underwater communications systems. It doesn't yet implement detection algorithms, but it is the first step in the development of an autonomous adaptive communication system.

Oceans form 2/3 of the surface area of our planet. Our understanding of this environment even after several decades of research is best described as rudimentary. The watery abyss is home to the world's largest and most diverse biological ecosystems. Monitoring of these ecosystems and study of the physical and biological evolution of the oceans is of paramount importance to increased comprehension and understanding of the oceans. Efficient monitoring relies on the collection of data over long… Show more

Oceans form 2/3 of the surface area of our planet. Our understanding of this environment even after several decades of research is best described as rudimentary. The watery abyss is home to the world's largest and most diverse biological ecosystems. Monitoring of these ecosystems and study of the physical and biological evolution of the oceans is of paramount importance to increased comprehension and understanding of the oceans. Efficient monitoring relies on the collection of data over long periods of time and in diverse sea conditions. Stationary or moving sonar systems have proven invaluable for this task. However, most systems are fixed in their mode of operation, possessing little or no flexibility. Thus, when the environment changes data retrieval becomes difficult or impossible. Changing the characteristics of the monitoring device to match the local sea conditions is a possible solution to this problem. In this paper the hardware and software implementation of a system that realises this function is presented together with some preliminary transmission tests in the Mediterranean Sea. The system, VERTLINK is designed to collect, store and transmit physical and bio-acoustical data to an end-user. The system, a half-duplex underwater communication link, comprises two units-a sea-bed unit and a surface unit. The sea-bed unit, under the control of the surface unit, records oceanographic data and then transmits it to the sea-surface unit. The latter is linked to a computer station on-board a survey vessel via a physical cable or to shore station by means of a radio link. Using this system the end-user is able to change the way the sea-floor unit acquires and transmits data. The modulation rate/technique can be changed from 2-DPSK to 8-DPSK, allowing data retrieval to be changed according to sea noise conditions. The power level can be varied from 20% to 100%, to achieve more efficient use of power resources and the sea-floor unit can be told to release. Show less

Abstract:
For the last thirty years ocean bottom seismometers (OBSs) have been used to survey the oceans. However, the quality of the data they produce is often degraded due to poor coupling or high levels of ambient noise. In contrast, sensors placed beneath the seafloor avoid many of these problems. For the last two decades burials have relied on Ocean Drilling Program (ODP) boreholes. This approach is expensive and demands numerous human resources. In addition, the locations of these… Show more

Abstract:
For the last thirty years ocean bottom seismometers (OBSs) have been used to survey the oceans. However, the quality of the data they produce is often degraded due to poor coupling or high levels of ambient noise. In contrast, sensors placed beneath the seafloor avoid many of these problems. For the last two decades burials have relied on Ocean Drilling Program (ODP) boreholes. This approach is expensive and demands numerous human resources. In addition, the locations of these boreholes, determined by the ODP, are rarely desirable for monitoring seismic activity. In this paper a sub-bottom seismic acquisition system is presented that uses free-fall devices, or deep ocean seismic penetrators (DOSP), to place sensors several tens of metres beneath the seafloor. The DOSPs weigh approximately 1800 kg, achieve terminal velocities between 30-50 m/s and penetrate to depths of 20-30 metres in soft sea sediments. Once buried, they record seismic activity and transmit data back to the surface using a frequency shift keyed (FSK) modulation technique. The results of an experiment conducted in the Mediterranean using this system are presented. These confirm the predicted dynamic and kinematic behaviour of the DOSP and allow an assessment of the ambient seismic noise level at a depth of 30 metres beneath the seafloor. In conclusion this paper discusses the potential use of free-fall devices to increase our understanding of processes in the deep oceans, with particular emphasis on their applicability to future deep ocean seismology Show less

Abstract: In this paper the combined finite element-boundary element method is applied to the analysis of the sound-structure interaction around a multi-layered anechoic baffle. The baffle is made of three layers: an aluminium backing supports a second layer of highly butyl rubber. The third layer, loaded polyurethane, presents a regular grid of steep shaped cones with a fluid-matching function. The viscoelastic materials are fully modelled into the finite element method using linear integral… Show more

Abstract: In this paper the combined finite element-boundary element method is applied to the analysis of the sound-structure interaction around a multi-layered anechoic baffle. The baffle is made of three layers: an aluminium backing supports a second layer of highly butyl rubber. The third layer, loaded polyurethane, presents a regular grid of steep shaped cones with a fluid-matching function. The viscoelastic materials are fully modelled into the finite element method using linear integral constitutive relationships. The combined FE-BE algorithm is based on a partial application of the Burton and Miller Helmholtz gradient formulation to overcome non-uniqueness problems. Examples of analysis of acoustic scattering in a range of frequencies typical of underwater communications are given together with a practical application of the structure Show less

Abstract: Underwater the only effective means of transmitting signals is acoustically. This century man has exploited this principle and developed a wide range of sonar systems for tasks such as underwater communication, sea bottom profiling and target detection. However, these systems when compared to the sonar systems of dolphins are rudimentary. The primary sensory system of a dolphin is acoustic and can be likened to the function of the human eye, in that a dolphin will use an acoustic… Show more

Abstract: Underwater the only effective means of transmitting signals is acoustically. This century man has exploited this principle and developed a wide range of sonar systems for tasks such as underwater communication, sea bottom profiling and target detection. However, these systems when compared to the sonar systems of dolphins are rudimentary. The primary sensory system of a dolphin is acoustic and can be likened to the function of the human eye, in that a dolphin will use an acoustic signal to visualise its environment. The exact nature and purpose of most of the acoustic vocalisations of dolphins are poorly understood. It is known that dolphins can distinguish between objects of different shape, density and wall thickness using echolocation clicks. However, little is known about their wide repertoire of other acoustical signals. In this paper a DSP system that allows a real time analysis of the frequency composition of dolphin vocalisations is presented. The system, designed and built around ADSP 21020, digitises dolphin vocalisations at a rate of 44100 Hz, generates a N-point FFT and displays the results as a rolling spectrogram. Using this system enhanced interpretation and greater insight into the structure of cetacean vocalisations has been possible and has enabled the identification of what is thought by the authors to be new dolphin vocalisation. This vocalisation is of the correct time duration and frequency composition to suggest that it is a Doppler sensitive pulse used by dolphins to track and follow their prey Show less

Abstract: The current generation of underwater telemetry systems tend to use proven low data rate `discrete-component' designs. These systems perform well under static conditions, but their performance rapidly degenerates when the environment in which they are used becomes more dynamic. The next generation of underwater telemetry systems will be adaptive and combat dynamic effects by processing signals using complex detection algorithms. The next step in the evolution of underwater… Show more

Abstract: The current generation of underwater telemetry systems tend to use proven low data rate `discrete-component' designs. These systems perform well under static conditions, but their performance rapidly degenerates when the environment in which they are used becomes more dynamic. The next generation of underwater telemetry systems will be adaptive and combat dynamic effects by processing signals using complex detection algorithms. The next step in the evolution of underwater communication systems is the development of systems that adapt automatically to changes in the environment and execute algorithms in real time which will encode, detect and decode transmitted signals more efficiently. This paper presents a DSP-based underwater communication system that uses four `Analogue Devices' digital signal processors to control the transmission, modulation and demodulation of data from a sea-bottom unit to a surface receiver. The system uses multiphase 2, 4 or 8 differential phase shift keying (DPSK) and can be viewed as the first stage in the development of an adaptive underwater system that will more effectively combat the effects of the dynamic underwater environment Show less