Effect of Hurricane Michael on the Underwater Acoustic Environment of the Scotian Shelf

Abstract

In October 2000 DRDC Atlantic carried out a detailed characterization of the shallow water environment in a 150 by 170 km area of the Scotian Shelf. The study area was centered at 44 deg. N, 61 deg. W and had an average water depth of 70 m. In addition to oceanographic moorings, two rapid environmental assessment surveys of water temperature profiles were made from Canadian maritime patrol aircraft which dropped 72 air-expendable baththermographs (AXBTs) in an 8 by 9 grid with 16 km nominal spacing. Between the AXBT surveys on Oct. 14 and 21, hurricane Michael passed over the study area. The AXBT surveys and satellite-derived sea surface temperature imagery show that passage of the hurricane cooled surface waters and changed the thickness of the mixed layer by up to 10 m. The effect of the environmental change on acoustical propagation in the 20 Hz to 10 kHz band was estimated by calculating broadband transmission loss with the PROLOS normal modes model using sound speed profiles measured before and after the hurricane and using climatological profiles.