Publication Date:
2022-05-25
Description:
A study was carried out to quantify the level of numerical noise in numerical scattering
chamber (NSC) calculations and to compare these noise levels with signal levels of body
waves, interface waves and ambient noise. The amplitudes of signal and noise in snapshots
from the numerical scattering chamber were quantified at 50 and 65 periods for a few
reference models. Models with homogeneous subseafloor structure were studied to determine
the level of numerical noise; models with a wavenumber-correlation length product of one
were examined to determine signal levels. Models were run with both Higdon and telegraph
equation absorbing boundaries since the numerical noise within the grid depends on the
boundary formulation. Amplitudes were measured along data traces obtained at a grid depth
of 3.33 λw and at the seafloor. Forward traveling head waves had typical amplitudes of ±125
but may reached ±250 near the direct wave. Diffraction amplitudes were observed up to
±300. Stoneley wave amplitudes ranged from ±800 up to ±20,000. Numerical noise levels
were less than ±25 in most areas of the water and less than ±350 along most of the seafloor.
Regardless of the absorbing boundary type, however, there was a region of noise extending
up to 15 λw behind the first seafloor reflection at 3.33 λw in which noise levels range from
±100 up to ±600. In this region it is difficult to resolve signal from systematic numerical
noise.
Description:
This work was carried out under ONR Grant #N00014-90-J-1493
Keywords:
Underwater acoustics
;
Scattering
Repository Name:
Woods Hole Open Access Server
Type:
Working Paper
