Abstract
This paper presents single receiver geoacoustic inversion of two independent data sets recorded during the 2017 seabed characterization experiment on the New England Mud Patch. In the experimental area, the water depth is around 70 m, and the seabed is characterized by an upper layer of fine grained sediments with clay (i.e., mud). The first data set considered in this paper is a combustive sound source signal, and the second is a chirp emitted by a J15 source. These two data sets provide differing information on the geoacoustic properties of the seabed, as a result of their differing frequency content, and the dispersion properties of the environment. For both data sets, source/receiver range is about 7 km, and modal time-frequency dispersion curves are estimated using warping. Estimated dispersion curves are then used as input data for a Bayesian trans-dimensional inversion algorithm. Subbottom layering and geoacoustic parameters (sound speed and density) are thus inferred from the data. This paper highlights important properties of the mud, consistent with independent in situ measurements. It also demonstrates how information content differs for two data sets collected on reciprocal tracks, but with different acoustic sources and modal content.
Highlights
W HAT is mud? Any child would come with a quick and trivial answer: mud is a brown sticky thing, fun to play with
The two studies were conducted on different tracks, but they consistently indicate that the sound-speed ratio at the mud/water interface is slightly lower than 1, and that a positive strong gradient is required in the mud layer to fit the data
The present paper focuses on geoacoustic inversion of modal TF dispersion curves
Summary
W HAT is mud? Any child would come with a quick and trivial answer: mud is a brown sticky thing, fun to play with. The main objectives of SBCEX are first, to understand the physical mechanisms that control sound propagation in mud, second, to quantify uncertainties in estimated seabed model parameters, and third, to assess the resulting geoacoustic models and inversion methods. The second study [20] was performed at shorter range (r ∼ 5 km), and warping was used to resolve up to mode number 18 over the frequency band 20–440 Hz. The two studies were conducted on different tracks, but they consistently indicate that the sound-speed ratio at the mud/water interface is slightly lower than 1, and that a positive strong gradient is required in the mud layer to fit the data (this will be questioned later in this paper).
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