Antoni Mànuel

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The S-transform is becoming popular for time-frequency analysis and data-adaptive filtering thanks to its simplicity. While this transform works well in the continuous domain, its discrete version may fail to achieve accurate results. This paper compares and contrasts this transform with the better known continuous wavelet transform, and defines a relation between both. This connection allows a better understanding of the S-transform, and makes it possible to employ the wavelet reconstruction formula as a new inverse S-transform and to propose several methods to solve some of the main limitations of the discrete S-transform, such as its restriction to linear frequency sampling.

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A suitable sampling technology to identify species and to estimate population dynamics based on individual counts at different temporal levels in relation to habitat variations is increasingly important for fishery management and biodiversity studies. In the past two decades, as interest in exploring the oceans for valuable resources and in protecting these resources from overexploitation have grown, the number of cabled (permanent) submarine multiparametric platforms with video stations has increased. Prior to the development of seafloor observatories, the majority of autonomous stations were battery powered and stored data locally. The recently installed low-cost, multiparametric, expandable, cabled coastal Seafloor Observatory (OBSEA), located 4 km off of Vilanova i la Gertrú, Barcelona, at a depth of 20 m, is directly connected to a ground station by a telecommunication cable; thus, it is not affected by the limitations associated with previous observation technologies. OBSEA is part of the European Multidisciplinary Seafloor Observatory (EMSO) infrastructure, and its activities are included among the Network of Excellence of the European Seas Observatory NETwork (ESONET). OBSEA enables remote, long-term, and continuous surveys of the local ecosystem by acquiring synchronous multiparametric habitat data and bio-data with the following sensors: Conductivity-Temperature-Depth (CTD) sensors for salinity, temperature, and pressure; Acoustic Doppler Current Profilers (ADCP) for current speed and direction, including a turbidity meter and a fluorometer (for the determination of chlorophyll concentration); a hydrophone; a seismometer; and finally, a video camera for automated image analysis in relation to species classification and tracking. Images can be monitored in real time, and all data can be stored for future studies. In this article, the various components of OBSEA are described, including its hardware (the sensors and the network of marine and land nodes), software (data acquisition, transmission, processing, and storage), and multiparametric measurement (habitat and bio-data time series) capabilities. A one-month multiparametric survey of habitat parameters was conducted during 2009 and 2010 to demonstrate these functions. An automated video image analysis protocol was also developed for fish counting in the water column, a method that can be used with cabled coastal observatories working with still images. Finally, bio-data time series were coupled with data from other oceanographic sensors to demonstrate the utility of OBSEA in studies of ecosystem dynamics.

-Transform From a Wavelet Point of View

The aim of this paper is to present a study on the potential and limits of the -transform and its inverses. The S-transform is an extension of the short-time Fourier transform with characteristics of the wavelet transform. It is mostly used for time-frequency analyses. Two different inverse S-transforms have been presented in the literature. We explain why the most recent one is an approximation but a very good one. The level of approximation is calculated in this paper. We then discuss the relative merits of both inverses. A careful study enables us to show that, although both inverses are nearly exact in the infinite continuous domain, this is not true anymore in the practical finite discrete domain. Side effects are quantified, and typical examples are given. Time-frequency filtering is one of the main applications of the S-transform. We evaluate the effects that occur when using the S-transform and its inverses for filtering.

The new seafloor observatory (OBSEA) for remote and long-term coastal ecosystem monitoring

Radio frequency identification (RFID) devices are currently used to quantify several traits of animal behaviour with potential applications for the study of marine organisms. To date, behavioural studies with marine organisms are rare because of the technical difficulty of propagating radio waves within the saltwater medium. We present a novel RFID tracking system to study the burrowing behaviour of a valuable fishery resource, the Norway lobster (Nephrops norvegicus L.). The system consists of a network of six controllers, each handling a group of seven antennas. That network was placed below a microcosm tank that recreated important features typical of Nephrops’ grounds, such as the presence of multiple burrows. The animals carried a passive transponder attached to their telson, operating at 13.56 MHz. The tracking system was implemented to concurrently report the behaviour of up to three individuals, in terms of their travelled distances in a specified unit of time and their preferential positioning within the antenna network. To do so, the controllers worked in parallel to send the antenna data to a computer via a USB connection. The tracking accuracy of the system was evaluated by concurrently recording the animals’ behaviour with automated video imaging. During the two experiments, each lasting approximately one week, two different groups of three animals each showed a variable burrow occupancy and a nocturnal displacement under a standard photoperiod regime (12 h light:12 h dark), measured using the RFID method. Similar results were obtained with the video imaging. Our implemented RFID system was therefore capable of efficiently tracking the tested organisms and has a good potential for use on a wide variety of other marine organisms of commercial, aquaculture, and ecological interest.

The S -Transform and Its Inverses: Side Effects of Discretizing and Filtering

The utility and cost-effectiveness of instrument networks are enhanced by instrument interoperability. Todays oceanographic instruments are characterized by very diverse non-standard software protocols and data formats. This diversity of protocols poses serious challenges to integration of large-scale sensor networks. Standard instrument protocols are now being developed to address these challenges. Some of these standards apply at the IP-network level and enable integration of existing “lower level” proprietary instrument protocols and software components. Other approaches are intended to be implemented by the instrument device itself. These native instrument protocol standards offer the possibility of more uniform and simpler system architectures. We compare these various approaches, describe how they can be combined with one another, and describe some prototypes that implement them.

A New Laboratory Radio Frequency Identification (RFID) System for Behavioural Tracking of Marine Organisms

This paper discusses the use of the IEEE 1588 standard in ocean observatories. The performance result of prototype implementations of this standard in an Ethernet Marine Sensor Network (MSN) is presented. The performance tests emulate an underwater-cabled observatory with a Master Clock synchronized with GPS, located in an on-shore station, and with underwater instruments requiring high-precision PPS (pulse s−1) signals for synchronization purposes. These signals will be provided to the underwater station by an IEEE 1588 GPS Emulator connected to the observatorys Local Area Network (LAN). The experimental setup emulates the underwater-cabled observatory OBSEA where this technology will be installed due to synchronization requirements of marine instruments such as ocean bottom seismometers.

Instrument interface standards for interoperable ocean sensor networks

The jitter test of waveform recorders and analog-to-digital converters (ADCs) is traditionally carried out using one of the methods recommended in the IEEE standard for digitizing waveform recorders, i.e., IEEE Standard 1057. Here, we study the uncertainty of one of those methods, point out the bias inherent to the estimator recommended for measuring the ADC jitter, and suggest an alternate estimator. Expressions are also presented for the determination of the precision of a given estimate from the number of samples used, the standard deviation of the additive noise present in the test setup, the jitter standard deviation, and the stimulus signal parameters. In addition, an expression for the computation of the minimum number of samples required to guarantee a given bound on the estimation uncertainty is presented, which is useful in optimizing the duration of the test.

Precision timing in ocean sensor systems

The Ocean Bottom Seismometer (OBS) is a key instrument for the geophysical study of sea sub-bottom layers. At present, more reliable autonomous instruments capable of recording underwater for long periods of time and therefore handling large data storage are needed. This paper presents a new Ocean Bottom Seismometer designed to be used in long duration seismic surveys. Power consumption and noise level of the acquisition system are the key points to optimize the autonomy and the data quality. To achieve our goals, a new low power data logger with high resolution and Signal–to-Noise Ratio (SNR) based on Compact Flash memory card is designed to enable continuous data acquisition. The equipment represents the achievement of joint work from different scientific and technological disciplines as electronics, mechanics, acoustics, communications, information technology, marine geophysics, etc. This easy to handle and sophisticated equipment allows the recording of useful controlled source and passive seismic data, as well as other time varying data, with multiple applications in marine environment research. We have been working on a series of prototypes for ten years to improve many of the aspects that make the equipment easy to handle and useful to work in deep-water areas. Ocean Bottom Seismometers (OBS) have received growing attention from the geoscience community during the last forty years. OBS sensors recording motion of the ocean floor hold key information in order to study offshore seismicity and to explore the Earth’s crust. In a seismic survey, a series of OBSs are placed on the seabed of the area under study, where they record either natural seismic activity or acoustic signals generated by compressed air-guns on the ocean surface. The resulting data sets are subsequently used to model both the earthquake locations and the crustal structure.

IEEE 1057 Jitter Test of Waveform Recorders

The implementation of a FPGA based fuzzy controller for DC/DC converters is described in this paper. The fuzzy control developed is evaluated with experimental measurements of the closed loop performance of a buck DC/DC converter in respect of the line and load regulation.

Ocean Bottom Seismometer: Design and Test of a Measurement System for Marine Seismology

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