| Spatial and Temporal Variability in Bottom Roughness: Implications to High Frequency Subcritical Penetration and Backscatter |
20 SEP 2002 |
9 pages |
| Authors:
Kevin L. Williams; Darrell R. Jackson; Eric I. Thorsos; Dajun Tang; Kevin B. Briggs; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS
|
 | Quantitative prediction of high frequency, low grazing angle penetration into, and scattering from, sand sediments requires knowledge of the roughness of the water/sand interface. Since the sediment roughness evolves due to hydrodynamic and biological processes, concurrent, co-located measurement of roughness and acoustic penetration/backscattering is essential for testing acoustic models or using such models to determine the likelihood of buried target detection. Here, we examine both roughness and acoustic measurements carried ... |
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| NRL-APL Grain Size Algorithm Upgrade |
28 JUN 2002 |
38 pages |
| Authors:
Kevin B. Briggs; Darrell R. Jackson; K. Y. Moravan; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
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| This upgrade was designed to improve upon older algorithms used to infer input geoacoustic parameters fro high-frequency acoustic models from sediment grain size. These older algorithms were based on limited data set and were developed by adjusting acoustic model-data fits rather than by statistical regression. The upgrade has two components. The regression analysis of sediment grain size and geoacoustic properties was performed by NRL and the determination of accuracy of ... |
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| Effects of Macrofauna on Acoustic Backscatter from the Seabed: Field Manipulations in West Sound, Orcas Island, WA, USA |
15 JUN 2001 |
26 pages |
| Authors:
Robert F. Self; Patrick A. Hearn; Peter A. Jumars; Darrell R. Jackson; Michael D. Richardson; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
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| Previous observations with a bottom-mounted, radially scanning sonar (BAMS) at 40 kHz suggested that macrofaunal activities influence low-angle, acoustic backscatter from seafloor sediments. In order to test that possibility experimentally, we measured and modeled time series of backscatter strength at both 40 and 300 kllz prior to manipulation and then introduced several macrofaunal species at Imown abundances to randomly selected locations within the ensonified area. We worked in West Sound, ... |
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| An Experiment in High-Frequency Sediment Acoustics: SAX99 |
APR 2001 |
11 pages |
| Authors:
Eric I. Thorsos; Kevin L. Williams; Darrell R. Jackson; Michael D. Richardson; Kevin B. Briggs; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A major high-frequency sediment acoustics experiment was conducted in shallow waters of the northeastern Gulf of Mexico. The experiment addressed high-frequency acoustic backscattering from the seafloor, acoustic penetration into the seafloor, and acoustic propagation within the seafloor. Extensive in situ measurements were made of the sediment geophysical properties and of the biological and hydrodynamic processes affecting the environment. An overview is given of the measurement program. Initial results from APL-UW ... |
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| Seasonal Temperature Gradients Within a Sandy Seafloor: Implications for Acoustic Propagation and Scattering |
10 NOV 2000 |
9 pages |
| Authors:
Darrell R. Jackson; Michael D. Richardson; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
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| Seafloor temperatures measured during the SAX99 experiment off Fort Walton Beach, Florida included sharp decreases in response to the passage of cold fronts. Sediment pore water temperatures exhibited an increasing temperature (3-40 deg C m(-1)) with depth in the sediment. By fitting a heat conduction model to the gradient data, the thermal diffusivity of the sediment was estimated to be 0.006 cm(2)s(-1). The effects of seasonal variations of sediment thermal ... |
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| High-Frequency Bistatic Scattering Model for Elastic Seafloors |
FEB 2000 |
45 pages |
| Authors:
Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A model for bistatic acoustic scattering at high frequencies (10-100 kHz) from elastic seafloors is developed by combining the elastic small-slope roughness scattering model of Yang and Broschat with the elastic volume scattering model of Ivakin. The combined model is applicable to a variety of seafloors, including clays, silts, sands, gravel, and rock. Although elastic effects are negligible in sands and finer sediments, they are ... |
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| Scattering of High-Frequency Acoustic Energy from Discrete Scatterers on the Seafloor: Glass Spheres and Shells |
1999 |
7 pages |
| Authors:
Michael E. Richardson; Kevin B. Briggs; Kevin L. Williams; Darrell R. Jackson; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
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| Shells and shell debris are common at the water/seafloor interface. Quantifying the scattering from shells is thus important for predicting high frequency backscattering from the seafloor. A backscattering experiment is described in which glass beads (radius equal to 1.75 cm) and shells (largest dimension tip to about 10 cm) were placed near a bottom-mounted sonar and backscattering examined as a function of the number of discrete scatterers Supported by Office ... |
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| Modeling of Subcritical Penetration into Sediments Due to Interface Roughness |
JUN 1997 |
8 pages |
| Authors:
Eric I. Thorsos; Darrell R. Jackson; John E. Moe; Kevin L. Williams; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| 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 water- sediment interface. Using perturbation theory, a numerically tractable three- dimensional model has been developed for simulating experiments. Data-model comparisons show that interface roughness is a viable hypothesis for the observed subcritical penetration. ... |
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| High-Resolution Benthic Acoustic Measurement System |
30 OCT 96 |
3 pages |
| Authors:
Darrell R. Jackson; Kevin L. Williams; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A new sonar system has been constructed and successfully fielded. The system, designated as the Accelerated Benthic Acoustic Measurement System (XBAMS), is an autonomous, bottom mounted, circularly scanning sonar that permits remote observation of benthic biological and physical processes over a large area (100 m diameter circle) and long times (weeks to months) in the littoral zone. |
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| High Resolution Benthic Acoustic Measurement System |
30 OCT 96 |
3 pages |
| Authors:
K. L. Williams; P. A. Jumars; Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| This is a one year project to improve methods of acoustic observation of benthic change by developing a bottom mounted, circularly scanning sonar that permits remote observation of benthic biological activity at sampling rates as high as 10 scans/hour. |
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| Effects of Shear Elasticity on Sea Bed Scattering: Numerical Examples |
16 AUG 96 |
37 pages |
| Authors:
Anatoliy N. Ivakin; Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| It is known that marine sediments can support both compressional and shear waves. However, published work on scattering from irregular elastic media has not examined the influence of shear on sea bed scattering in detail. A perturbation model previously developed by the authors for joint roughness volume scattering is used to study the effects of elasticity for three sea bed types: sedimentary rock, sand with high shear speed, and sand ... |
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| A Model for Bistatic Scattering into Ocean Sediments for Frequencies from 10 - 100 kHz |
JUN 96 |
41 pages |
| Authors:
Kevin L. Williams; Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A model is developed for bistatic scattering into ocean sediments by an acoustic source located in the water and a receiver buried in the bottom. The model is closely related to that developed by Jackson (1993) for a source and receiver that were both located in the water and parallels that effort in many regards. In particular, bottom scattering is treated as being due to interface roughness and volume inhomogeneity. ... |
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| Near Field Scattering Through and From 2-D Fluid-Fluid Rough Interface |
FEB 96 |
38 pages |
| Authors:
John E. Moe; Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| General analytical expressions for the time dependent field intensity scattered from or through (penetrating) a 2-D fluid-fluid rough surface due to a narrowband incident plane wave, and a narrowband point source area derived and expressed in terms of the bistatic scattering cross section per unit area of the rough surface. Even though the cross section is defined as a far field entity, this near field result is general and exact ... |
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| Measurement of High-Frequency Acoustic Scattering from Coastal Sediments |
96 |
8 pages |
| Authors:
Darrell R. Jackson; Kevin L. Williams; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| The focus of this work is measurement of monostatic and bistatic scattering from shallow water sediments. One objective is to use the scattering data to clarify mechanisms responsible for scattering. Another is to use the backscatter data to acoustically monitor physical and biological processes that affect the seafloor. During FY96, processing and interpretation of the Key West bistatic data was the major effort. In addition, backscatter model-data comparisons for ail ... |
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| The TEVA Experiment Cruise Report |
MAR 95 |
22 pages |
| Authors:
Peter H. Dahl; Darrell R. Jackson; Kevin L. Williams; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A team from APL-UW made monostatic reverberation and bistatic forward scattering measurements in a shallow water channel (depth 25.6 m) located within the Dry Tortugus collection of islands (24 deg 36.7'N 82 deg 50.7'W) during the period 9-17 February 1995. Accompanying the acoustic measurements were continuous measurements of wind speed and surface wave spectra, including wave directional information. The data will be used for sonar model development and model/data comparisons ... |
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| 100 Hz-10 kHz Bottom Backscattering Model: Generalized Treatment of Sediment Sound Propagation, Sediment Volume Scattering, and Interface-Roughness Scattering |
APR 94 |
35 pages |
| Authors:
Darrell R. Jackson; Paul D. Ingalis; Kou-Ying Moravan; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
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| A model for bottom backscattering strength in the frequency range 100 Hz to 10 kHz is presented. This model generalizes an earlier low-frequency model intended for the smaller frequency range 100-1000 Hz. The new model matches the predictions of an existing high-frequency model (10-100 kHz) but offers new insights into the effect of fine-scale layering. Scattering from both sediment volume inhomogeneity and interface roughness is included in the model. For ... |
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| Pencil Beam Array Development |
MAR 94 |
13 pages |
| Authors:
Terry E. Ewart; Eric I. Thorsos; Darrell R. Jackson; Leroy O. Olson; UNIV OF WASHINGTON SEATTLE COLL OF OCEAN AND FISHERY SCIENCES
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| During FY89 through FY94 we designed and partially constructed a transmit/receive array for imaging the ocean near-surface zone. During FY92-93, a proof-of-concept prototype with reduced numbers of transmit and receive elements was designed, fabricated and tested. Tests were conducted in local waters using a simple, fixed mooring. The final design of the array allowed for pan and tilt, and incorporated features for self-calibration and accurate position measurement. With this array ... |
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| Multi-Discipline Group Reverberation SRP FY89 Program |
13 APR 90 |
2 pages |
| Authors:
Terry E. Ewart; Eric I. Thorsos; Darrell R. Jackson; UNIV OF WASHINGTON SEATTLE
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| THE VALIDITY OF THE PERTURBATION APPROXIMATION FOR ROUGH SURFACE SCATTERING USING A GAUSSIAN ROUGHNESS SPECTRUM |
JUL 89 |
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| Authors:
Eric I. Thorsos; Darrell R. Jackson
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 | in this paper the validity of the perturbation approximation for rough surface scattering is examined (1) by comparison with exact results obtained by solving an integral equation and (2) through comparison of low-order perturbation predictions with higher-order predictions. (author/ntiac). |
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Reports by Author
