Underwater explosions detonated by the U.S. Navy to test the sturdiness of ships' hulls have provided seismologists with a test opportunity of their own: how much can we know about an underwater explosion from the seismic and acoustic data it generates?
In a study published in the Bulletin of the Seismological Society of America, a team of researchers led by Ross Heyburn of AWE Blacknest in the United Kingdom compared the "ground-truth" data available from the Navy on the location, size and depth of these detonations to estimates obtained from seismic stations and hydroacoustic sensors.
The explosions conducted off the Florida coast offer a chance to test the capabilities of the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty Organization, deployed to detect secret nuclear test explosions, say the authors.
"Underwater explosions of this size where ground-truth data are available are quite rare," said Heyburn. IMS stations "do record signals from many underwater events, both naturally occurring, like earthquakes, and man-made, like air-gun surveys. However, ground-truth data from the man-made sources are often not available, and usually any underwater explosions observed are much smaller in size than the Florida explosions."
The Navy explosion tests were conducted in 2001, 2008 and 2016 within the Navy's Mayport test area, located 120 kilometers off the coast of Jacksonville, Florida. The experiments tested the hull integrity of the near-shore combat ships the USS Jackson, the USS Milwaukee, the USS Winston Churchill and the USS Mesa Verde.
During the experiments, 10,000-pound chemical explosions were towed behind a vessel sailing alongside the combat ships, to test how the combat ship hulls responded to the shock waves produced by nearby detonations equivalent to a TNT charge weight of about 6759 kilograms.
The explosions aren't the size of a nuclear test explosion, but they are much larger than many of the other underwater explosions that are available to study, explained Heyburn.
"The explosions described in the paper are much smaller than a typical nuclear test explosion which is typically of the order of kilotons in TNT equivalent charge weight," he said.
"For comparison, naval mines and anti-submarine depth charges typically contain explosive charges with TNT equivalent charge weights of the order of hundreds of kilograms."
Heyburn and colleagues analyzed data from the explosions collected by IMS seismic stations around the globe and from a hydrophone station near Ascension Island in the South Atlantic Ocean for the tests in 2008 and 2016. The researchers used the location data provided by the Navy for several of the explosions as a way to improve the accuracy of calculations used to pinpoint the epicenter of explosions without available ground-truth data.
Previous research on detonations in the Dead Sea and other underwater test sites has shown that there is a relationship between the local magnitude of an explosion and its charge weight. After taking into account the salinity of the seawater near Florida, Heyburn and colleagues were able to modify the Dead Sea calculations to estimate the Navy charge weights from published estimates of local magnitude for the explosions.
Underwater explosions also produce unique seismic features that can be used to identify the source. One such notable feature is the bubble pulse, the underwater pulsing generated by the gas bubble created by the explosion as it expands and contracts in size. The researchers were able to identify the bubble pulse in the seismic records, confirming that the seismic signals were the result of an underwater explosion.
The bubble pulse was not observed as clearly at the Ascension Island hydrophone station, and Heyburn and colleagues suggest that the shallow waters off the Florida Coast may have distorted the hydroacoustic signals of the explosion. "This showed that both the seismic and hydroacoustic data can be important when analyzing signals from underwater explosions," said Heyburn.
Related Links
Seismological Society of America
Naval Warfare in the 21st Century
| Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.</span> |
||
| SpaceDaily Contributor $5 Billed Once credit card or paypal |
 |
SpaceDaily Monthly Supporter $5 Billed Monthly paypal only |
Navy awards $9B to HII, Bath Iron Works for 10 DDG 51-class destroyers
Washington (UPI) Oct 1, 2018
The U.S. Navy has tapped two companies, Huntington Ingalls Industries and Bath Iron Works, to build ten of it's Flight III Arleigh Burke-class destroyers over the next decade. The Navy awarded contracts to the two companies on Thursday worth about $9 billion - HII was awarded $5.1 billion for its six DDG 51-class vessels, with BIW's contract valued at $3.9 billion. The contracts cover engineering change proposals, design budgeting requirements and post-delivery availabilities for all te ... read more
from Military Space News, Nuclear Weapons, Missile Defense https://ift.tt/2ErqJmu
via space News
No comments: