Showing papers presented at "OCEANS Conference in 2012"

DESERT Underwater: An NS-Miracle-based framework to design, simulate, emulate and realize test-beds for underwater network protocols

Abstract: DESERT Underwater (short for DEsign, Simulate, Emulate and Realize Test-beds for Underwater network protocols) is a complete set of public C/C++ libraries to support the design and implementation of underwater network protocols. Its creation stems from the will to push the studies on underwater networking beyond simulations. Implementing research solutions on actual devices, in fact, is of key importance to realize a communication and networking architecture that allows heterogeneous nodes to communicate reliably in the underwater environment. In this paper, we first discuss the rationale behind this work, and, then we list and briefly describe all the DESERT Underwater libraries currently implemented. In line with the current trends in underwater networking, our approach makes it possible to reuse the same code prepared for simulations in order to realize underwater network prototypes. We also present some preliminary tests that confirm the feasibility of the proposed solution for the design and evaluation of underwater network protocols. In this perspective, we believe that DESERT Underwater is a useful tool to profitably develop and test real world applications.

Underwater wireless sensor networks

Abstract: Terrestrial wireless sensor networks (TWSNs) are subject to extensive research and development. Numerous applications take advantage of low-cost, small-sized, easily configurable and scalable TWSN nodes to monitor, detect, and track various environmental phenomena and events. The recent advancement in electronics and sensor miniaturization and low-power technologies enabled TWSNs to extend their reach to underwater applications. Underwater wireless sensor networks (UWSNs) can be used in many new applications. Yet, UWSNs development is dependent on a number of technological challenges that need to be overcome. In this paper, we present an overview of UWSNs, their applications, and their challenges. We also present a survey of various UWSN architectures currently used in deployed UWSN systems.

Channel-aware routing for underwater wireless networks

Abstract: This paper presents a new cross layer routing protocol for underwater wireless sensor networks. The solution, termed CARP for Channel-aware Routing Protocol, exploits link quality information for cross layer relay determination. Nodes are selected as relays if they have a (recent) history of successful transmissions to their neighbors. CARP combines link quality with simple topology information (hop count), thus being able to route around connectivity voids and shadow zones. The protocol is also designed to take advantage of power control for selecting robust links. The performance of CARP has been evaluated through ns2-based simulations, and compared to the performance of two previously proposed routing protocols, namely, FBR and DBR. Our results show that CARP robust relay selection mechanism enables it to achieve throughput efficiency that is up to twice the throughput of FBR and almost three times that of DBR. CARP also obtains remarkable performance improvements over FBR and DBR with respect to end-to-end packet latency and energy consumption.

Field experiments for Dynamic Source Routing: S2C EvoLogics modems run the SUN protocol using the DESERT Underwater libraries

Abstract: In this paper we present a performance evaluation and feasibility test of SUN, a routing protocol for underwater networks inspired to Dynamic Source Routing (DSR), to which it adds several features that improve its behavior in underwater environments The evaluation has been performed with real devices, and has been made possible through a collaboration between the Department of Information Engineering (DEI) of the University of Padova, Italy and EvoLogics GmbH, Germany In detail, the idea put in practice in this work is to command real hardware, ie, the S2C acoustic modems of EvoLogics, by means of the ns2/NS-Miracle engine developed and extensively used primarily by research institutions This approach favors code reuse and speeds up the realization of flexible and easily modifiable network prototypes Our results show that SUN can deal with typical network issues such as the disconnection of a node and the appearance of additional nodes, and that it copes well with dynamic topology changes

Autonomous landing of an Unmanned Aerial Vehicle on an autonomous marine vehicle

Abstract: In the recent past, there has been a lot of interest in developing UAVs (Unmanned Aerial Vehicles) to perform a variety of challenging tasks ranging from military defense, surveillance, environmental sensing, etc. This research is one that focuses on quadrotor UAVs deployed for environmental sensing in the oceans. We have developed an algorithm to autonomously control a quadrotor to track and land on the landing pad on a marine vehicle, an autonomous kayak. The algorithm takes up the challenge of tough landing conditions prevalent in the oceans due to winds and currents (causing the target to rock and drift). It has currently been developed for the commercially available AR Drone quadrotor. Landing pad sensing was achieved through image processing techniques using MATLAB. Testing has been carried out both indoors, and outdoors over open water, with a success rate of over 75%. This autonomous control algorithm for the quadrotor would enhance its operating region, preventing the need for it to fly back to the base station and thereby saving valuable flight time in far-off ocean deployments.

The UNET-2 modem — An extensible tool for underwater networking research

Abstract: Several decades of research in underwater communication and networking has resulted in novel and innovative solutions to combat challenges such as long delay spread, rapid channel variation, significant Doppler, high levels of non-Gaussian noise, limited bandwidth and long propagation delays. Many of the physical layer solutions can be tested by transmitting carefully designed signals, recording them after passing through the underwater channel, and then processing them offline using appropriate algorithms. However some solutions requiring online feedback to the transmitter cannot be tested without real-time processing capability in the field. Protocols and algorithms for underwater networking also require real-time communication capability for experimental testing. Although many modems are commercially available, they provide limited flexibility in physical layer signaling and sensing. They also provide limited control over the exact timing of transmission and reception, which can be critical for efficient implementation of some networking protocols with strict time constraints. To aid in our physical and higher layer research, we developed the UNET-2 software-defined modem with flexibility and extensibility as primary design objectives. We present the hardware and software architecture of the modem, focusing on the flexibility and adaptability that it provides researchers with. We describe the network stack that the modem uses, and show how it can also be used as a powerful tool for underwater network simulation. We illustrate the flexibility provided by the modem through a number of practical examples and experiments.

Acoustic communications and navigation under Arctic ice

Abstract: Initial results of experiments performed under Arctic ice have shown that acoustic communications and navigation can be performed on scales of 10–100 km using relatively inexpensive and compact hardware. Measurements of the impulse response at ranges of 10 and 75 km reveal extensive scatter and both resolvable and unresolvable rays. Phase coherent communication using adaptive equalization was successful up to ranges of 70–90 km at data rates of 5–10 b/s. As the SNR drops to levels too low for phase coherent communication, short FM sweeps (5–10 s), are shown to provide sufficient gain to provide lower rate communications and also support navigation.

Wave Energy Development Roadmap: Design to commercialization

Abstract: In order to promote and support development of the wave energy industry, Sandia National Laboratories (SNL) has developed a Wave Energy Development Roadmap. The Wave Energy Development Roadmap outlines the pathway from initial design to commercialization for Wave Energy Converter (WEC) technologies. Commercialization of a wave energy technology is embodied in the deployment of an array of WEC's, a WEC Farm. The development process is related to the commonly used metric of Technology Readiness Levels (TRLs). The roadmap incorporates modeling and experimental expectations at corresponding TRLs which provide a guide for the industry to pursue successful design optimizations, prototype deployments, and utility scale commercialization. The roadmap serves the additional purpose of pinpointing research gaps in the development process.

Measurement of micro-bathymetry with a GOPRO underwater stereo camera pair

Abstract: A GO-PRO underwater stereo camera kit has been used to measure the 3D topography (bathymetry) of a patch of seafloor producing a point cloud with a spatial data density of 15 measurements per 3 mm grid square and an standard deviation of less than 1 cm A GO-PRO camera is a fixed focus, 11 megapixel, still-frame (or 1080p high-definition video) camera, whose small form-factor and water-proof housing has made it popular with sports enthusiasts. A stereo camera kit is available providing a waterproof housing (to 61 m / 200 ft) for a pair of cameras. Measures of seafloor micro-bathymetry capable of resolving seafloor features less than 1 cm in amplitude were possible from the stereo reconstruction. Bathymetric measurements of this scale provide important ground-truth data and boundary condition information for modeling of larger scale processes whose details depend on small-scale variations. Examples include modeling of turbulent water layers, seafloor sediment transfer and acoustic backscatter from bathymetric echo sounders.

Impact of real modem characteristics on practical underwater MAC design

Abstract: The grand challenges posed by the adverse acoustic channels have been extensively studied in medium access control (MAC) design for underwater acoustic networks (UWANs). In recent years a bunch of MAC protocols have been proposed and analyzed to address the long propagation delay and constraint power supply problems. However, the challenges from the real acoustic modem characteristics are still neglected in the current research. Based on our experiments and sea trial tests with different modems — Teledyne Benthos modem, WHOI MicroModem and high speed UConn OFDM modem, we discover two important real system issues and discuss their significant effect on MAC design in UWANs. Experiment and simulation results reveal that the long preamble sequence feature of acoustic modems harm most existing MAC protocols with short packets, such as acknowledgment, notification, reservation used control packets. Other than reservation based methods are vulnerable to the long transmission time and busy terminal problem, the random access based protocols can benefit from them. As a result, Aloha based protocols yield encouraging throughput performance in UWANs and are reconsidered as viable solution for underwater MAC. Based on the analysis, simulation and experiment results, we also provide discussion on the direction of future MAC designs.

Object detection and tracking for autonomous underwater robots using weighted template matching

Abstract: Underwater environment has a noisy medium and limited light source, so underwater vision has disadvantages of the limited detection range and the poor visibility. However it is still attractive in close range detections, especially for navigation. Thus, in this paper, vision-based object detection (template matching) and tracking (mean shift tracking) techniques for underwater robots using artificial objects have been studied. Also, we propose a novel weighted correlation coefficient using the feature-based and color-based approaches to enhance the performance of template matching in various illumination conditions. The average color information is incorporated into template matching using original and texturized images to robustly calculate correlation coefficients. And the objects are recognized using multiple template-based selection approach. Finally, the experiments in a test pool have been conducted to demonstrate the performance of the proposed techniques using an underwater robot platform yShark made by KORDI.

Model predictive control of an autonomous underwater vehicle in an in situ estimated water current profile

Abstract: Autonomous underwater vehicle control actuation is attained through the use of various methods, including propellors, jets and control surfaces. In order for a vehicle to achieve a desired trajectory and fulfil the mission goals successfully, the input of commands to the control subsystem is needed. Model predictive control (MPC) [2] relies on having a function which determines the future vehicle poses to a horizon given the present vehicle pose, and control actions during this time, and then minimising a cost function, such as the squared distance from the predicted to desired vehicle path. The advantage of MPC over other control methods like PID, Linear Quadratic Regulator (LQR) and its derivatives, is that very little hand tuning is required [10]. The method outlined in [9] allows simultaenous estimates of the vehicle pose and the water current profile in the direction of the Acoustic Doppler Current Profiler (ADCP) beams, including small scale gradients in situ. The position, velocity, attitude and water current estimates from this localisation filter could be used to arrive at control commands in real-time to achieve the desired vehicle trajectory given the predicted water current acting on the vehicle and the vehicle pose for future states. Results in this paper show that even with large delays due to the MPC optimisation stage to arrive at control actions, the controller can accurately track the desired trajectory in the mean estimates from the localisation. The trajectory following accuracy is shown to be limited by the localisation error.

Simulation of non-White and non-Gaussian underwater ambient noise

Abstract: Noise in the ocean is the result of many contributions. Sources emitting sound in open sea as well as in a coastal area can be placed both in the sea surface and underwater. Excluding the self-noise, the noise impinging a sonar system is called ambient noise and usually is split in two groups: anthropic and natural. In this paper we focus in modeling noise produced by ship transit, which falls in the anthropic category, and noise due to sea surface agitation, that is classified as a natural source. In particular we aspire to simulate the acoustic noise radiated by the machinery of a vessel once the rotational speed of the propeller induces the cavitation effect. Further, we take account of the wind speed action in the sea state and its contribution to the actual underwater ambient noise. An algorithm based on a non-Gaussian approach allows to generate sequence of samples representative of a noise realization having specified kurtosis level and to reproduce the desired source spectrum. The results of the simulation suggest that the surface ship transit can be thought as a major factor in limiting the performance of a underwater acoustic communications systems operating in a coastal shallow waters scenario.

Data upload from a static Underwater network to an AUV: Polling or random access?

Abstract: In this paper, we consider data uploading from a network of fixed sensors to a mobile Autonomous Underwater Vehicle (AUV). We approach the problem using both random and controlled access: in particular, we propose UW-Polling, a data retrieval protocol based on controlled access, and evaluate it against channel access protocols based on random access. We compare the performance of these protocols in terms of throughput, Packet Delivery Ratio and energy consumption, discussing the impact of the source power level on these metrics. Our results show that our polling-based protocol outperforms the other protocols in several cases, and thereby confirm that polling is an effective approach to enable AUVs to retrieve data from a network of fixed sensors.

Design and test of a robust docking system for hovering AUVs

Abstract: This paper presents the conceptual idea and a developed prototype of a docking system for a hovering AUV (Autonomous Underwater Vehicle). The presented docking system passively assists the vehicle's docking procedure by guiding it into a defined position, where it is mechanically locked in place by one of the station's actuators. In its final position the docking system provides an electrical power supply and a broadband data link to the AUV. The developed concept additionally enables differently shaped AUVs to use the same docking station.

On feature extraction and region matching for forward scan sonar imaging

Abstract: Automated processing of sonar video imagery enables valuable capabilities for a wide variety of underwater applications in turbid environments. Some key examples comprise the detection, localization and tracking of distinct scene targets, building feature maps, as well as improving positioning accuracy of unmanned submarines by means of image registration and 3D motion estimation to augment traditional positioning devices. This work offers a novel technique for the registration of 2D forward-look sonar images, by optimization over the sonar 3D motion parameters. It incorporates landmark detection through an adaptive clustering scheme with Gaussian map to represent key features at each frame. Improved performance is demonstrated in experiments with real data, both in terms of computation time and accuracy, relative to the state of the art, where the registration utilizes a simplified 2D image transformation model. Among many potentials, the method can improve precision in AUV navigation and environmental modeling.

Underwater acoustic sensor network for early warning generation

Abstract: There is an ever felt need to create an efficient comprehensive system to tackle natural hazards such as Tsunamis, earthquakes, landslides and floods by providing a timely early warning. Underwater wireless sensor network (UWSN) seems to be one promising solution. The success of mobile wireless communication in terms of power efficiency and reliability needs to be repeated with the UWSN for fighting the havoc of nature. An integrated system for early warning generation which would provide information globally is proposed. This paper highlights the physical layer challenges in establishing a reliable, low power consuming and long life UWSN system for early warning generation.

Automated optimal processing of phase differencing side-scan sonar data using the Most-Probable Angle Algorithm

Abstract: Phase-differencing side-scan sonar systems produce co-located bathymetry in addition to each side-scan amplitude measurement. Bathymetric soundings are calculated from the range to each measurement (derived from the two-way travel time) and the receive angle of the incoming signal. Because phase-differencing systems produce a seafloor sounding with each individual measurement, they are often characterized as noisy when compared to multi-beam sonar systems, whose seafloor estimates, whether by amplitude-weighted mean or sub-aperture phase difference detection, are the product of averaging several measurements. In addition, every effort is made to increase the resolution of side-scan data by increasing the bandwidth and sampling rate of the transmitted signal, often producing more than 10,000 data points per ping. This volume of outlier-prone, relatively noisy data is difficult for operators to interpret and software to process. A series of methods has been developed for the automated processing of phase-differencing side-scan sonar data producing seafloor estimates and related uncertainties optimized for the survey application. The “Most-Probable Angle Algorithm” (MPAA) has been developed for the filtering of outliers in range-angle measurements. With outliers removed, the uncertainty of the filtered measurements are estimated. Angle estimates are then calculated as an uncertainty-weighted mean where the number of measurements contributing to each estimate is determined from that required to achieve a desired depth uncertainty. The resulting swath of depth measurements contains irregularly spaced soundings, typically obtaining full spatial resolution of the side-scan data from 20–50 degrees from nadir, and combining several measurements to reduce the uncertainty elsewhere. In this way, given a survey requirement, an optimal amount of information can be extracted from the sonar data in varying conditions.

Bio-inspired pressure sensing for active yaw control of underwater vehicles

Abstract: A towed underwater vehicle equipped with a bio-inspired artificial lateral line (ALL) was constructed and tested with the goal of active detection and correction of the vehicle's angle of attack. Preliminary experiments demonstrate that a low number of sensors are sufficient to enable the discrimination between different orientations, and that a basic proportional controller is capable of keeping the vehicle aligned with the direction of flow. We propose that a model based controller could be developed to improve system response. Toward this, we derive a vehicle model based on a first-order 3D Rankine Source Panel Method, which is shown to be competent in estimating the pressure field in the region of interest during motion at constant angles of attack, and during execution of dynamic maneuvers. To solve the inverse problem of estimating the vehicle orientation given specific pressure measurements, an Unscented Kalman Filter is developed around the model. It is shown to provide a close estimation of the vehicle state using experimentally collected pressure measurements. This demonstrates that an artificial lateral line is a promising technology for dynamically mediating the angle of a body relative to the oncoming flow.

Impact of a wave farm on its local grid: Voltage limits, flicker level and power fluctuations

Abstract: Significant electrical power fluctuations in the range of seconds may be generated by most oscillating wave energy converters without significant amounts of energy storage capacity. Because of these fluctuations, a wave farm may have a negative impact on the power quality of the local grid to which it is connected. Hence, the impact of these devices on both distribution and transmission networks needs to be well understood, before large scale wave farms can be allowed to connect to the grid. This paper details a case study on the impact of a wave farm on the distribution grid around the national wave test site of Ireland with respect to voltage and power fluctuations, as well as regarding flicker levels. The electrical power output of the oscillating water column (OWC) wave energy converters was derived from experimental time series produced in the context of the FP7 project “CORES”. The results presented in this paper are based on a typical time series. Simulations were performed using DIgSILENT simulation tool “PowerFactory”.

ROVs and AUVs in support of marine renewable technologies

Abstract: This paper presents a discussion of the challenges involved in the support of offshore marine renewable technology installations and how recent developments in autonomous underwater vehicles (AUVs) and innovative remotely operated vehicles (ROVs) provide a unique technical solution to address those challenges. A description of Bluefin Robotics' AUVs is presented along with relevant data that show the effectiveness of the technology in these environments. Bluefin has recently partnered with Hawkes Ocean Technologies (HOT), and the paper provides a detailed description of the Hawkes Remotes line of low-footprint, high-speed ROVs that can similarly address the unique challenges of the offshore marine renewables market.

Spatial ontologies for detecting abnormal maritime behaviour

Abstract: The upsurge in piracy and the impact of recent environmental disasters have highlighted the need to improve maritime surveillance. Governmental and private initiatives have developed monitoring systems with improved acquisition and analysis capabilities. These systems rely on one major component, namely the detection of abnormal ship behaviour. This implies a detailed formalisation of expert knowledge. However, the quantity of data, the complexity of situations, the failure to take into account their spatial characteristics and the potential for the same scenario to be interpreted in different ways have proved to be significant problems. We therefore propose a new prototype for the analysis of abnormal ship behaviour. The system is based on a spatial ontology associated with a geographical inference engine. It automatically identifies suspicious vessels and associates them with probable behaviours defined by operational staff.

Advancements in high-performance timing for long term underwater experiments: A comparison of chip scale atomic clocks to traditional microprocessor-compensated crystal oscillators

Abstract: We discuss the merits and performance of two commercially available time bases — a microprocessor-compensated crystal oscillator designed and manufactured by Seascan, Inc. of Falmouth, MA, and a chip-scale atomic clock (CSAC), designed and manufactured by Symmetricom, Inc. of San Jose, CA — for use in autonomous underwater instrumentation. Over the last ∼10 years, the WHOI Ocean Bottom Seismology group has used the Seascan time base in its fleet of ∼100 Ocean-Bottom Seismographs (OBS), and has acquired a record of Seascan performance amounting to over 183 cumulative seafloor years and over 25 years of cumulative test time in a temperature-chamber across 120 clocks. These data show that the Seascan clocks perform within their quoted specification in almost all cases, and if carefully selected can provide performance significantly exceeding their specifications, all at a very modest 5 mW of power consumption. Our testing has also shown some unexpected effects in certain units that may undermine timing quality if not understood and controlled. Within the last year or so, chip-scale atomic clocks have become available, and we have installed these time bases in 15 OBS. These CSACs offer two orders of magnitude improvement in precision, at the cost of significantly greater power consumption (∼120 mW). We have deployed thirteen instruments on the ocean floor for a 6-month experiment using CSACs as the time base. In addition we have tested 4 more units in the lab. Based on the performance that we have seen in the field and in the lab, both time bases are worthy of consideration in new ocean instrumentation. As expected, the CSACs show better stability, lower aging, and better temperature response, at the expense of higher power consumption. This paper will present a detailed comparison of both clocks, showing the tradeoffs that need to be considered when selecting a time base. We will also look at techniques available to improve the aggregate performance of the Seascan time bases to well above their nominal specifications.

Asynchronous multiuser reception for OFDM in underwater acoustic communications

Abstract: Recently significant progress has been made on point-to-point underwater acoustic communications, and the interest has grown on the application of those techniques in multiuser communication settings, where the asynchronous nature of multiuser communication poses a grand challenge. This paper develops a time-asynchronous multiuser reception approach for orthogonal frequency division multiplexing (OFDM) transmissions in underwater acoustic channels. The received data burst is segmented and apportioned to multiple processing units in an overlapped fashion, where the length of the processing unit depends on the maximum asynchronism among users on the OFDM block level. Interference cancellation is adopted to reduce the interblock interference between overlapped processing units. Within each processing unit, the residual inter-block interference from multiple users is aggregated as one external interference which can be parameterized. Multiuser channel estimation, data detection, and interference mitigation are then carried out in an iterative fashion. With asynchronous multiuser transmissions, simulation and experimental results clearly demonstrate the impact of the maximum relative delay among users on the receiver performance.

Online speed optimization for sailing yachts using extremum seeking

Abstract: This paper briefly presents the main points on the development and testing of an extremum seeking controller used to maximize the longitudinal velocity of surface sailing vehicles by changing the angle of the sail. The algorithm is suitable for sailing purposes since it requires only the measurements of the vehicle's velocity and the sail angle. As an illustration, we present a few simulation results on our previously-obtained sailing yacht simulator, which was developed based on a 4 DOF nonlinear dynamic model for surface sailing vehicles, showing that the proposed extremum seeking controller is capable of maximizing the sailing yacht's speed performance through online sail tuning. Furthermore, the proposed sail optimization algorithm is tested at sea on an experimental platform, i.e. a small scale autonomous sailboat, illustrating the potential of the controller.

New insights into the physical drivers of wave runup from a continuously operating terrestrial laser scanner

Abstract: A dune-mounted terrestrial laser scanner was used to investigate the physical drivers of runup on an intermediate beach under a variety of wave conditions. Specifically, the laser is automated to collect hourly, simultaneous observations of beach morphology and hydrodynamics in the swash and inner surf-zone. A strong tidal signal in de-tided runup statistics is observed such that the 2% exceedence runup elevation and mean swash elevation is higher at high tide than at low tide for the same given wave conditions. This is similar to the significant incident band wave height (Hs in ) at the base of the foreshore, which also showed a similar strong tidal dependence. In fact, our results suggest that mean swash elevation and incident band swash scale well with Hs in , though correlations are slightly improved when beach foreshore slope is included in predictions of incident band swash (r2 = 0.73 vs 0.69). In contrast, the Stockdon et al., 2006 relationship, which is based on beach foreshore slope, offshore wave height, and wavelength, only explained 53% of the variance in our data even when beach slope was known. Similar to Stockdon et al., we found infragravity band swash was dependent on deep water wave height and wave length. These data suggest that increased or decreased breaking over the sandbar at low and high tides, respectively, may filter the amount of energy left in the incident band to be transferred to runup at the shoreline. The implications of this sandbar filtering are that up-to-date bathymetry or a quantification of dissipation across the surfzone is necessary to produce accurate real-time runup predictions.

Conceptual design of ocean compressed air energy storage system

Abstract: In this paper, an ocean compressed air energy storage (OCAES) system is introduced as a utility scale energy storage option for electricity generated by wind, ocean currents, tides, and waves off the coast of North Carolina. Geographically, a location from 40km to 70km off the coast of Cape Hatteras is shown to be a good location for an OCAES system. Based on existing compressed air energy storage (CAES) system designs, a conceptual design of an OCAES system with thermal energy storage (TES) is presented. A simple thermodynamic analysis is presented for an adiabatic CAES system which shows that the overall efficiency is 65.9%. In addition, finite element simulations are presented which show the flow induced loads which will be experienced by OCAES air containers on the ocean floor. We discuss the fact that the combination of the buoyancy force and the flow induced lift forces (due to ocean currents) generates a periodic loading on the storage container and seabed, and how this presents engineering challenges related to the development of adequate anchoring systems. We also present a system, based on hydrolysis, which can be used for storing energy (in the form of oxygen and hydrogen gas) in containers on the ocean floor.

Non-recurrent wideband continuous active sonar

Abstract: This paper presents a continuous active sonar (CAS) waveform which enables high revisit rates and wideband processing gains to be achieved with suppression of range-ambiguous returns. Non-recurrent wideband linear FM signals with circular Costas frequency-staggering across chirp repetition intervals is shown to provide ambiguity functions with good Doppler and range resolution, controllable Doppler and range ambiguities, and a high revisit rate. These slow-time Costas or “SLO-CO” CAS waveforms allow for the possibility of updating range-velocity estimates every pulse repetition interval while achieving the clutter suppression associated with the use of conventional wideband LFM signals.

Development and field testing of laser-induced breakdown spectroscopy for in situ multi-element analysis at sea

Abstract: The application of laser-induced plasmas has been investigated as a mechanism to perform in situ, multi-element chemical analysis of liquids and immersed solids at sea during marine surveys. Analytically useful spectra have been observed from plasmas generated by irradiation of a high power pulsed laser in both bulk liquids and immersed solids using a single pulse at hydrostatic pressures of up to 30MPa. Experiments were performed at sea using the in situ laser-induced breakdown spectroscopy (LIBS) device I-SEA (In situ Seafloor Element Analyser) mounted on-board the remotely operated vehicle (ROV) Hyper-Dolphin of the Japan Agency for Marine Science and Technology (JAMSTEC). During the sea trials real-time, multielement analysis was successfully achieved for the first time for both liquids and immersed solids at a depth of 200 m.

High frequency RF based non-contact underwater communication

Abstract: Although electromagnetic wave, especially high frequency electromagnetic wave suffers great attenuation in sea water, it has advantages of high reliability and high speed in short distance and non-contact communication situations, such as AUV (Autonomous Underwater Vehicle) docking systems and wet-mate connectors. This paper discusses the propagation characteristic of high frequency RF in sea water. Computational and experimental results of an underwater high frequency RF system are presented. The findings offer intuitive insights for the design of a non-contact communication system which transfers data in high speed and high reliability in sea water. Specifically, this paper begins with theoretical calculation of the propagation path. Then, the communication system is modeled in the finite analysis software ANSOFT HFSS to study the characteristic of the electromagnetic field and to evaluate the influence of insulation. The simulation model has been experimentally validated by comparing the computed available range against the measured data based on the water tank test.