Airborne Anti-Submarine Warfare by Michael E. Glynn

Author:Michael E. Glynn
Language: eng
Format: epub
Tags: HISTORY / Military / Naval
Publisher: Frontline Books
Published: 2022-05-30T00:00:00+00:00

50%

1,200ft

22ft /sec

80%

1,800ft

33ft /sec

Source: ‘’Reference Publication 33’’

The SSP found in conditions that produce convergence zones generate refraction that tends to focus sound into reswept zones and raises the local SPL. However, as sound moves through the ocean, it still suffers TL. As a result, for aviators to exploit convergence zones, the target submarine must have radiated noise levels loud enough that even after TL is taken into account, there is still sufficiently high signal strength for detection to occur in the reswept zones.

ASW aircraft exploited convergence zones extensively during the Cold War. This was due in part to the high radiated noise levels of Soviet nuclear submarines. These searches often took place in deep water with sufficient depth and sound speed excess to support convergence zone formation. Improved quieting of nuclear submarines and the proliferation of quiet SSKs have lowered the radiated noise levels of nearly all modern submarines. Many smaller navies from developing nations operate in shallow waters, where convergence zone contact is not possible because of a lack of depth excess. As a result, convergence zone is still a possible arrival path for aviators to exploit. However, it much less prevalent in tactical scenarios today than it was several decades ago for the reasons listed above.30

Reliable Acoustic Path

Acousticians refer to direct path contact between a shallow source and a deep sensor or a deep source and a shallow sensor as the Reliable Acoustic Path, or RAP. This arrival path is referred to as “reliable” because it is not susceptible to near-surface effects or subject to bottom losses.31 ASW forces take advantage of RAP in the intermediate ranges, beyond short-range direct path tracking but closer than convergence zone contact.

RAP has been the subject of renewed focus in the past two decades. As submarines became quieter in the 1980s and 1990s, convergence zone contact became less and less common and the ability of long-range cueing sensors to exploit the DSC decreased as well. This forced some ASW forces to shift from using small numbers of large fixed arrays for long-range detection and cueing and instead deploy networks of many small sensors deep in the ocean to exploit the RAP over intermediate ranges.32

Bathymetric Features

We have already alluded to the fact that the seafloor has a large effect on sound propagation. The ocean bottom reflects, scatters, and absorbs sound waves. It can channel and block acoustic energy. Let us examine the tactical implications of various bottom types and bathymetric features.

Close to the coast, the ocean bottom slopes gently away from the land, forming an area known as the Continental Shelf. This shelf may extend for only a short distance or for many dozens of miles. Eventually, the shelf drops away sharply from the surface, forming an area known as the Continental Slope. This sharp discontinuity from the Continental Shelf to the steep Continental Slope is known as the Shelf Break. Continental Shelves are generally relatively flat, although they may be interrupted in places by submarine canyons, ridges, and terraces.

The slope of the Continental

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