Browsing Reprints by Issue Date
Now showing items 301-320 of 548
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Texture analysis of sidescan sonar imagery using statistical scattering models
(NATO. SACLANTCEN, 1997)It is shown that the generalised K-distribution provides a good fir to the amplrtude statisttcs of sonar imagery from several different types of seabed sediment. A number of possible explanations for the Ricean nature of ... -
Seabed survey by VHR multichannel seismics: GEOSIS project
(NATO. SACLANTCEN, 1997)Site surveys prior to the installation of offshore facilities are required to obtain shallow soil structural and geotechnical information. The French project GEOSIS was aimed at improving both geophysical and geotechnical ... -
Attenuation of shear waves in near-surface sediments
(NATO. SACLANTCEN, 1997)In situ measurement of compressional and shear speed and compressional attenuation in near-surface marine sediments is a well-developed technology but techniques required to measure shear attenuation have lagged behind. ... -
Autofocusing a synthetic aperture sonar using the temporal and spatial coherence of seafloor reverberation
(NATO. SACLANTCEN, 1997)An autofocusing algorithm for the compensation of translational motion errors of a sea floor rmaging synthetic aperture side scan sonar is presented. The algorithm does not depend on the presence or absence of dominant ... -
Analysis of broad-band echosounder data over a gassy seabed
(NATO. SACLANTCEN, 1997)Calibrated echosoundings from a well-characterized gassy seabed were examined. Acoustic reflection was significantly higher than expected. It is hypothesized that gas bubbles are responsible. Anomalously high levels of ... -
Wavefront curvature ranging as a passive synthetic aperture problem
(NATO. SACLANTCEN, 1997)A new method of wavefront curvature passive ranging is introduced that is based on a model-based approach. The signal and measurement systems are placed into state-space form, thereby allowing the unknown parameters of the ... -
Time domain finite difference methods for range dependent Biot media
(NATO. SACLANTCEN, 1997)The physics of sound propagation in saturated, porous (Biot) media differs from propagation in fluids and elastic/anelastic solids because of the existence of a second compressional wave, the "slow" wave. Many environments ... -
An experimental investigation of the contribution of sediment volume scattering to acoustic backscatter measured in the shallow waters of the Florida Strait
(NATO. SACLANTCEN, 1997)Experiments were conducted in the Florida Strait region of the United States in July 1995 for the purpose of investigating the contribution of sediment volume scattering to measured backscatter levels at frequencies between ... -
Estimation of chirp sonar signal attenuation for classification of marine sediments: improved spectral ratio method
(NATO. SACLANTCEN, 1997)Remote sediment classification through acoustic methods is of great interest for a few years. The attenuation coefficient of the transmitted wave is an important feature to characterize physical sediment layers properties. ... -
A novel method to enlarge the scanning region of a focused beamformer
(NATO. SACLANTCEN, 1997)Often focused beamforming systems use the Fresnel approximation to compute the required delays. Unfortunately, such an approximation has a validity region that is very narrow around the broadside direction. To investrgate ... -
Small scale volumetric inhomogeneities of shallow water sediments: measurements and discussion
(NATO. SACLANTCEN, 1997)There is a consensus that high-frequency acoustic scattering by the ocean bottom is partly due to sediment volumetric inhomogeneities, r e., random fluctuations in sediment sound speed and density. Understanding the spatial ... -
Measurement and interpretation of angular spreading from multiple boundary interactions in a shallow water channel
(NATO. SACLANTCEN, 1997)The problem of angular spreading of sound that has undergone multiple boundary scattering (both sea surface and sea bed) in a shallow water channel is discussed. Measurements made of the horizontal spatial coherence along ... -
A unified model for seabed volume and roughness scattering
(NATO. SACLANTCEN, 1997)Seabed scattering is considered taking into account perturbations of different type: volume inhomogeneities and roughness of the interfaces. A description is given in terms of plane waves. The first-order perturbation ... -
Bottom/subbottom surveying using a new, parametric, sidescan sonar
(NATO. SACLANTCEN, 1997)The Naval Research Laboratory (NRL) has developed a dual-frequency, towed, interferometric, sidescan sonar system known as the Subbottom Swath System, which is capable of detecting objects and structures buried below the ... -
Multipath field representation for seabed parameter extraction using backscatter data from shadow zones
(NATO. SACLANTCEN, 1997)Inversion strategies for bottom parameter estimation in shallow water impose stringent requirements on accuracy and speed of acoustic models. We highlight the importance of second order effects as first order determinants ... -
Modeling of subcritical penetration into sediments due to interface roughness
(NATO. SACLANTCEN, 1997)Recent experimental results reveal acoustic penetration into sandy sediments at grazing angles below the critical angle. We have been investigating a mechanism for subcritical penetration based on scattering at a rough ... -
Results from the use of broad-band, sub-bottom seismic data with statistically based sediment classification techniques
(NATO. SACLANTCEN, 1997)The QTC VIEW sediment classification system has been applied to shallow, high resolution seismic data recorded with the IKB-SEISTEC profiler from the navigable channel of the St. Lawrence estuary in Canada. A number of 10 ... -
High frequency acoustic propagation in coastal waters
(NATO. SACLANTCEN, 1997)High Frequency Acoustic Propagation experiments were performed with bottom-mounted sources and receivers at different coastal sites. A measurement technique has been developed and propagation loss data have been taken using ... -
Autonomous underwater vehicles for port protection
(NURC, 2006/07)NATO's present capability to deal with a terrorist threat to our ports is slow, dangerous, and inefficient. Ports are a challenging area within which to conduct MCM operations due to several factors: shipping movements, ... -
Adaptive normalization of active sonar data
(NURC, 2006/08)In active sonar detection the background interference is reduced through normalization prior to applying a detection threshold. From the two mainstream normalization algorithms, i.e. the sliding window and the split window, ...