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.
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...
Active sonar system performance in the presence of strong direct blast, or reverberations from the projected waveform, is considered. The presence of these reverberations may severely limit target detection performance and the applicability of the continuous active sonar (CAS) paradigm. Signal processing approaches to detect objects of interest and estimate relevant target parameters are described...
HF radar current measurements systems are in widespread use around the world providing very useful data sets for many applications. Data quality is generally good although sometimes the data are noisy especially at the edges of the spatial coverage. New approaches to the quality control of these measurements to remove noisy results or replace them with more reliable estimates, for both direction-finding...
This paper deals with underwater acoustic communication, and especially details an innovative approach for off the shelves existing modems performances evaluation. The originality is to be able to predict the operational performances of existing acoustic modems in a real complex situation, without sea trials.
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...
The Oceanographic Systems Laboratory at Woods Hole Oceanographic Institution has developed a low-power multi-frequency sonar board capable of operating at a wide range of frequencies from 200 KHz to 2 MHz and suitable for a wide range of applications. Its features include a transmitter, a receiver with gain control, a 24 MHz analog-to-digital converter, a programmable down converter capable of demodulating...
Orthogonal frequency division multiplexing (OFDM) implicitly assumes that the channel used for signal transmission is linear and time-invariant for the length of each OFDM symbol. This is necessary for the channel matrix to be diagonalizable via the DFT, under cyclic prefix. The underwater acoustic channel is highly time-variant due to platform motion and environmental fluctuations. As a result, the...
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...
In the last years a lot of interest has grown concerning the exploitation of data acquired by multiple sensors belonging to multistatic or Multiple Input Multiple Output systems. Indeed increased information and/or better performance can be retrieved using a network of cooperating sensors. In this paper, data acquired by a pair of Inverse Synthetic Aperture Radar sensors is exploited to estimate both...
The intersymbol interference (ISI) caused by multipath propagation becomes the major challenge for designing efficient equalization methods for underwater acoustic communications. Even at moderate bit-rates, the computational complexity of adaptive equalizers is high enough to challenge their realtime implementation. Hence, reducing their complexity by either low-complexity algorithms or efficient...
In this paper, a channel model used to develop a high-speed underwater acoustic MIMO communication link is described. A low-complexity stochastic model is controlled to fully characterize a doubly spread behaviour with extreme variations and over a long period interval. Key parameters of the stochastic channel model are extracted from seaport measurements taken in the Bedford Basin in Halifax. Using...
This paper reports the results of the sea experiments and the performance verification of the navigation method for wide area survey of seafloor using multiple autonomous underwater vehicles (AUVs). It has been difficult for conventional navigation methods such as dead reckoning or inertial navigation to achieve wide area survey with high positioning accuracy by only AUVs. In the method, as the AUVs...
The knowledge of the impulse response of the propagation channel is required for many underwater applications as communication, sonar detection and localization, marine mammals monitoring, etc. In the context of target classification, this impulse response informs about the relative motion between the source/receiver and the target through the Doppler effect. Knowing the emitted signal, the Doppler...
Based on the joint information of space-time-frequency, a novel scheme is proposed for localizing the low-frequency tone noise sources of an underwater moving vehicle by using a small aperture circular array. First, the Doppler signals formed when the noise sources pass through the closest point of approach (CPA), are separated in time domain with superdirectivity beamforming. Thereafter, processing...
The paper focuses on similarities and difference between adaptive threshold and sub-look processing in ship detection by Synthetic Aperture Radar (SAR). The main goal is to formalize the cascade application of both methods to achieve an overall reduction of the false alarm rate. The methods are tested on TerraSAR-X stripmap SAR data collected over the Gulf of Naples, Italy. Input parameters are set...
Pulse-to-pulse coherent Doppler sonar has been used to provide accurate velocity information, but the occurrence of “range-velocity” ambiguity seriously limits more general applications. Although multi-frequency and dual-time-interval methods have been used to enlarge the range of ambiguity velocity, it remains limited. Therefore, a combined method of conventional and coherent Doppler sonar using...
This paper dresses the implementation of an orthogonal frequency division multiplexing (OFDM) based multicarrier UWA communication system adopting a novel transform called T-transform. It combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthogonal unitary transform which increases channel diversity order without sacrificing any throughput. The...
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.