Direct measurement of sediment sound speed in Shallow Water '06

Abstract

Knowledge of sediment sound speed is crucial for predicting sound propagation. During the Shallow Water '06 experiment, in situ sediment sound speed was measured using the Sediment Acoustic-speed Measurement System (SAMS). SAMS consists of ten fixed sources and one receiver that can reach a maximal sediment depth of 3m. Measurements were made in the frequency range 2–35kHz. Signal arrival times and propagation distances were recorded, from which sediment sound speed was determined. Preliminary results from three deployments show that SAMS was capable of determining sediment sound speed with uncertainties less than 1.6%. Little dispersion in sediment sound speed was observed.

Observations of the R reflector and sediment interface reflection at the Shallow Water ’06 Central Site

“…However, the estimates of −20 log 10 ͉R 13 ͉ are very consistent with the presence of a thin, 20-cm layer overlying a half-space speed of 1630 m / s. Two direct (ground truth) measurements of sound speed were made within a 50 m radius of station 12 [see Fig. 1(b)], 8 using a 2 -11-kHz low-frequency (LF) and 10-21-kHz mid-frequency (MF) probe pulse in each case averaging to a depth of 1.6 m into seafloor. In one case the LF and MF speeds were estimated as 1615 and 1622 m / s, respectively, and in the other the LF and MF speeds were estimated as 1598 and 1599 m / s, respectively, with an uncertainty of approximately ±10 m / s applying to all estimates.…”

“…6 At this SW06 site, seafloor sand is confined to a thin ͑ϳ20 cm͒ winnowed layer 5,7 rather than to a thicker, O͑1͒ m, sand sheet typical of sand ridge sites. 5,6 For these reasons, the initial comparison of our results is limited to the direct in situ measurements of sound speed made within the same 0.3 km radius 8 during SW06. Interpretation and forward modeling of our results are guided by the stratigraphic constraints provided by closely spaced ͑50 m͒ chirp seismic reflection profiles that provide pseudo three-dimensional coverage of the SW06 central site.…”

Short range travel time geoacoustic inversion with vertical line array

“…Many geoacoustic inversion studies have been done on the New Jersey Shelf previously. Due to the variability of the seabed properties from location to location, 8 we only compare our estimates with most recent relevant works [8][9][10] near MPL-VLA1. Overall, the sound speed estimates are consistent with in situ sound speed measurements 9 made about 250 m from MPL-VLA1 ͑1615± 9 m / s and 1598± 11 m / s) in the frequency band 2 -11 kHz.…”

Modelling acoustic scattering, sound speed, and attenuation in gassy soft marine sediments

“…There is a broad range of reported values covering a variety of marine sediments [22][23][24][25][26][27][28][29][30][31][32][33] although the reported values of p are not consistent between experiments, most probably because of the different sediment types and frequency ranges considered. The value of p is frequently reported as representing a linear model of attenuation (e.g.…”