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On the width of a ray

2007; Acoustical Society of America; Volume: 122; Issue: 3 Linguagem: Inglês

10.1121/1.2764465

1520-9024

Irina I. Rypina, Michael G. Brown,

Microwave Imaging and Scattering Analysis

Consistent with earlier work by Kravtsov and Orlov, a simple general expression for the width of a Fresnel zone δrF in a smooth inhomogeneous environment is derived; this is the diffractive contribution to the width of a ray. In a stratified environment at long range, the general Fresnel zone width expression is shown to reduce approximately to one that is proportional to ∣α∣r(R−r)∕σ where α is the ray stability parameter, σ is the acoustic frequency, r is the range from the source to the field point of interest, and R is the source to receiver range. In a stratified environment on which a weak small-scale perturbation is superimposed, deterministic rays in the background environment that connect fixed end points break up into bundles of micromultipaths at moderate to long range and a second, scattering-induced, contribution δrs to the width of a ray must be considered. It is shown that δrs is proportional to ∣α∣r(R−r) and argued that in a micromultipathing environment the total effective width of a background ray is δrtot=δrF2+δrs2. Theoretical predictions are shown to agree well with travel-time sensitivity kernel calculations.