The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
This paper introduces the Smart Electronic Interface for Web Enabled Ocean Sensor Systems of the NeXOS project as example how interoperable standards help, to facilitate the creation of an infrastructure for sharing oceanographic observation data and the integration of sensor into marine installations. A given kind of sensor may be deployed on various platforms such as floats, gliders or moorings,...
Sonar performance prediction and detection analysis rely on statistical models for noise, reverberation and signal. Often the central limit theorem is exploited to simplify the modeling. For example, noise and reverberation can be represented by a Gaussian distribution (i.e., Rayleigh-distributed envelope) when they arise from a multitude of sources. Signal models are often limited to the extremes...
Unlike conventional Pulsed Active Sonar (PAS), which listens for target echoes in between short-burst transmissions, High Duty Cycle (HDC) sonar attempts to detect echoes amidst the continual interference from source(s) transmitting with nearly 100% duty cycle. HDC sonar presents an additional processing parameter, not available with PAS, which is the processing interval. The processing interval is...
Continous Active Sonar (CAS) system are bi-static systems that transmit high duty cycle waveforms so as to constantly process target echoes and revisit the target scene more frequently than conventional Pulsed Active Sonar (PAS) systems. This paper presents novel pulse train waveforms and adaptive processing methods for CAS systems. The pulse trains are composed of Generalized Sinusoidal Frequency...
In this paper we present a technique for underwater acoustic beamforming based on soundfield recording that encodes both the temporal and spatial characteristics of a signal. Here, we introduce the basic theory behind soundfield recording and present a first-order beamformer that beamforms the encoded data in a specific direction (θ,φ) and with a variable polar pattern, p. The appeal of this beamformer...
Continuous active sonar (CAS) is a special case of active sonar where the ping duration approaches the ping repetition interval. Sub-band processing is a method of breaking up the long-duration CAS transmission to achieve faster processing update rates than pulsed active sonar (PAS). This paper compares experimental signal-to-reverberation ratio (SRR) measured for CAS and PAS echoes. The processing...
A real demand for underwater acoustic (UWA) communications exists in oceanography, ocean exploration and undersea navigation. A new Doppler resilient digital communication, based on quadratic frequency modulations (QFM) is presented. The binary information is transmitted using two orthogonal QFM chirps. This signal modulation is suitable for low-data-rate communication such as telemetry. The first...
Coherence under varied circumstances is compared for two classes of waveform: linear FM chirps (a conventional sonar waveform) and binary phase shift keyed messages (a conventional acoustic communications waveform). All but the waveforms' time domain structure is kept constant during the comparison. Both modeled results as well as data from a large undersea array of hydrophones are presented. Parameters...
Radiated underwater noise of a trawler has been measured with the purpose of investigating the characteristics of the radiated noise of fishing vessels in order to understand the relative large variations in catch rates of the vessels that are experienced. In addition to the standard analysis, the investigation includes studies of how the noise level varies with distance between vessel and hydrophone...
Compared with the well-established techniques for underwater acoustic communication, underwater wireless optical communication provides much higher transmission bandwidth and can be an interesting alternative in short range underwater applications. We experimentally investigated the feasibility of using a directly modulated semiconductor laser as the transmitter in an underwater wireless optical communication...
In this work we review Filtered Multitone modulation (FMT) for underwater communications. This multicarrier modulation splits the transmission across several sub-bands with high spectral containment, and may be thought of as a hybrid between the widely popular single-carrier and OFDM schemes. As in OFDM the receiver architecture is conceptually based on a bank of filters, but in our envisaged scenarios...
The relationship between synthetic aperture sonar (SAS) image resolution and target-detection performance is quantified. It is first demonstrated how a lower-resolution SAS system can be simulated in a principled manner by band-limiting the image wavenumber spectrum of a full-resolution SAS image. This insight enables a direct comparison of target-detection performance in imagery of different resolutions...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.