Reprints: Recent submissions
Now showing items 321-340 of 548
-
Statistical evaluation of 80 kHz shallow-water seafloor reverberation
(NATO. SACLANTCEN, 1997)In this work a comparison is presented between 80 kHz reverberation statistics obtained at shallow water sites around Sardinia and Sicily. The data include measurements from several distinct bottom provinces, including ... -
Shallow-water seafloor characterization for high-frequency multibeam echosounder: image segmentation using angular backscatter
(NATO. SACLANTCEN, 1997)Sonar images from multibeam echosounders are submitted to various degradations, partly due to the sensor itself: Signal artefacts and corresponding corrections are presented, both for signal processing and for array ... -
Measurement of the bubble population in coastal waters using combination frequencies of MHz order
(NATO. SACLANTCEN, 1997)This paper describes the use of a combinatron frequency technique to measure the size distribution of oceanic bubbles. Written between two sea trials, the paper describes how the apparatus cart be adapted to design tests ... -
Ray tracing on a mini-computer
(NATO. SACLANTCEN, 1972/05)It would appear that most people engaged in solving problems in ray- tracing, use programs written for large computers. These machines commonly have large memory si~es, fast cycle times and large word length . This paper ... -
Advances in cots side scan sonar for MCM applications
(NATO. SACLANTCEN, 1997)The Persian Gulf War has elevated the awareness to the problems of shallow water mine detection. Today's high technology shallow water anti-invasion mines, such as the Italian made "MANTA" and the Swedish manufactured ... -
Numerical modelling of acoustic scattering by smooth inclusions in a layered fluid-solid medium
(NATO. SACLANTCEN, 1997)A boundary integral equation (BIE) method as descnbed for computing the scattering of a monofrequent acoustic field by a smooth, rigid 30 object in a layered range-independent fluid-solid medium. The BIE is discretized ... -
Modeling range-dependent, high-frequency, shallow-water torpedo reverberation data
(NATO. SACLANTCEN, 1997)The high-frequency, forward bottom losses predicted by a lossy Rayleigh and a Biot poroelastic sediment model are substantially different. These differences will accumulate and become measurable in multiple bottom bounce ... -
Temporal fluctuation of backscattered field due to bioturbatioon in marine sediments
(NATO. SACLANTCEN, 1997)Biological activity in marine sediments creates a time-varying, randomly fluctuating medium. A bio-diffusive model is proposed for predicting the temporal and spatial spectrum of sediment density fluctuations. Perturbation ... -
Areal seabed classification using backscatter angular response at 95kHz
(NATO. SACLANTCEN, 1997)A sediment classification scheme is developed based on the angular response (AR) of the seabed backscatter strength. The AR is characterised based on its mean level and slope over predefined angular sectors, and the presence ... -
Relating in situ shear wave velocity to void ratio and grain size for unconsolidated marine sediments
(NATO. SACLANTCEN, 1997)Recent advances in field hardware have meant that it has become possible to measurein situ shear wave velocity in the upper few decimetres of sea floor sediment in a routine manner. It is known that shear wave velocity can ... -
Wavelet analysis of side scan sonar imagery for classification
(NATO. SACLANTCEN, 1997)Wavelet-based techniques are presented for compressing side scan sonar images communicated from UUV's through band limited communication channels. Testing with an automatrc classifier on reconstructed images demonstrates ... -
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 ... -
A noise directionality model including variable bathymetry
(NATO. SACLANTCEN, 1997)In this paper we investigate the noise directionality due to distributed surface sources m several envtronments with a uniformly sloping sea bed. Of particular interest are frequency dependence and the question of the ... -
Retrodirective array performance case studies and implications for mine countermeasures
(NATO. SACLANTCEN, 1997)The use of focused acoustic fields for the mechanical destruction of fluid-borne targets is applied zn. the medical field for the comminution of kidney stones by lithotripsy. Inhomogeneities in the propagation medzum are ... -
Source and receiver responses in boreholes
(NATO. SACLANTCEN, 1997)This report considers the acoustic interaction between the acoustic freld rn a borehole and the elastic field in the surrounding formation. The problem with acoustic-seismic radration of energy from a source in a fluid ... -
High frequency matched field processing
(NATO. SACLANTCEN, 1997)Results are discussed from a high frequency (0 9-5 7 kHz), very shallow water (<10 m) experiment exploring the feasibility of carrying out matched field processing in this frequency and water depth regime The data was ... -
Dynamic attenuation extraction of seafloor sediments from very high resolution acoustic data
(NATO. SACLANTCEN, 1997)An approach to acquire geophysical information of seabed sediments as derrved from acoustic attenuation rs described. Using thefrequencies corresponding to the signal power spectrum maximum and a point 3 dB below, signal ... -
Effect of waveform on synthetic aperture sonar performance
(NATO. SACLANTCEN, 1997)This paper describes the main properties of the synthetic aperture sidescan sonar and highlights performances and limitations related to sonar features for mine counter measures. Attention is focused on the theoretical ... -
Very-high (cm scale) resolution multichannel seismology
(NATO. SACLANTCEN, 1997)