Transmission loss for the Beaufort Lens and the critica frequency for mode propagation during ICEX-18
Abstract
Complexities of acoustic propagation in ducts have long been known, e.g., shallow water environments and deep waters off Gibraltar. The “Beaufort Lens” (Lens) is a duct north of Alaska with nominal depths between 60 and 200 m and is reachable by oceanographic instruments and underwater unmanned vehicles and submarines. Propagation within the ducts is governed by waveguide physics. The frequencies must be high enough to support the modes within them such that there is a “critical frequency” (CF) where modes start to “detach” from surface loss mechanisms. Therefore, transmission losses (TLs) can abruptly decrease once a mode “fits” within a duct. This paper describes an experimental part of Ice Exercise 2018 supported by the U.S. Navy's Arctic Submarine Laboratory. The signals were transmitted from Camp Sargo north of Prudhoe Bay to the submarines SSN Hartford, SSN Connecticut, and HMS Trenchant. The data indicate low TLs near 100 Hz and an abrupt 10 dB decrease in TLs 244–280 Hz, both suggesting CFs. Modeling suggests CFs for modes 1 near 100 Hz and a higher CF when modes 3–6 “cascade” into the Lens starting near 250 Hz. There are also abrupt increases in TLs at other frequencies, which are explained by nulls in the product of the mode functions.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2022
- Source ID
- 10.1121/10.0010049
Entities
People
- Arthur Bernard Baggeroer
- Jon M. Collis
Organizations
- Massachusetts Institute of Technology
- Office of Naval Research