Acoustic backscatter measurements from littoral seabeds at shallow grazing angles at 4 and 8 kHz

Abstract

Direct measurement of acoustic scattering from the seabed at shallow grazing angles and low kilohertz frequencies presents a considerable challenge in littoral waters. Specifically, returns from the air-water interface typically contaminate the signals of interest. To address this issue, DRDC Atlantic has developed a sea-going research system for measuring acoustic scatter from the seabed in shallow-water environs. The system, known as the wideband sonar (WBS), consists of a parametric array transmitter and a superdirective receiver. In this paper, backscatter measurements obtained with the WBS at two sandy, shallow-water sites off North America's Atlantic coast are presented. Data were collected at 4 and 8 kHz at grazing angles from 3 degrees-15 degrees. The backscattering strength is similar at both sites and, below about 8 degrees, it appears to be independent of frequency within the statistical accuracy of the data. The measurements show reasonable agreement with model estimates of backscatter from sandy sediments. A small data set was collected at one of the sites to examine the feasibility of using the WBS to measure the azimuthal variability of acoustic scatter. The data set--although limited--indicates that the parametric array's narrow beamwidth makes the system well-suited to this task.

50 kHz bottom backscattering measurements from two types of artificially roughened sandy bottoms

“…7 as a default in the absence of bottom roughness measurement, have been widely used in model predictions of bottom backscattering due to the difficulty in obtaining these measurements. 14,24) The goal of this study was to investigate the dependence of backscattering strength on sediment interface roughness. Measurements of bottom backscattering strengths using 50 kHz continuous waves were made on a 0.5-m-thick sandy bottom in a water tank (dimension: 5 × 5 × 5 m 3 ) located at Hanyang University, Ansan, Korea.…”

Acoustic scattering modeling and sound field characteristics of rough seafloor in shallow sea

“…进入 21世纪以来, 海底声散射测量及相关技术研发受 到很多国家的广泛重视. Pecknold等 [14] 观测了加 拿大盆地的海底散射现象, Yu等 [15] 测量了中国南 黄海宽带砂底的反向散射特征. 另外, 由于中低频 声呐在水声通信、水下探测等方面的广泛应用, 研 究者们将研究重点转向了10 kHz以下的海底声散 射的测量和研究 [12,[16][17][18] .…”

Calibration sphere for low-frequency parametric sonars

“…In some of the very few cases where it is addressed, measurements have been made of the difference-frequency source level, 4,5 and range and/or angular dependence of the transmit field. 11,27 These measurements have been made by a hydrophone, which itself requires calibration. At other ranges and angles where knowledge of the difference-frequency field is required, models may be exercised, for example, those of Moffett and Mellon 28 or by means of the Bergen Code.…”

“…Another, larger class of applications exploits the properties of parametric sonar in backscattering, hence over a two-way path. These include acoustic scattering by the sea surface, 6,7 water column, 8 bottom as in the determination of geoacoustic properties 6,[9][10][11] and seafloor characterization, [12][13][14] and seabed vegetation. 15 Some other backscattering applications include sub-bottom profiling, 16 detection of objects on and in the seabed, [17][18][19][20][21] and marine archaeology.…”