Open AccessTransmission loss for the Beaufort Lens and the critica frequency for mode propagation during ICEX-18
Author(s) -
Arthur B. Baggeroer,
Jon M. Collis
Publication year - 2022
Publication title -
the journal of the acoustical society of america/the journal of the acoustical society of america
Language(s) - English
Resource type - Journals
eISSN - 1520-8524
pISSN - 0001-4966
DOI - 10.1121/10.0010049
Subject(s) - submarine , transmission loss , geology , bay , duct (anatomy) , underwater , lens (geology) , oceanography , arctic , hydrophone , acoustics , seismology , physics , optics , marine engineering , engineering , paleontology , medicine , pathology
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 [Formula: see text] and an abrupt 10 dB decrease in TLs 244–280 Hz, both suggesting CFs. Modeling suggests CFs for modes 1 near [Formula: see text] and a higher CF when modes 3–6 “cascade” into the Lens starting near [Formula: see text]. There are also abrupt increases in TLs at other frequencies, which are explained by nulls in the product of the mode functions.