Hydroacoustic Propagation and Reflection Loss Using Explosions Found in the Indian Ocean
Abstract
We investigate propagation and reflection loss using hydroacoustic waves from explosion sources in the Indian Ocean recorded at the International Monitoring System's (IMS) hydrophone stations. We developed a discovery procedure that searches the automatic processing results from the International Data Centre (IDC) for signals that match explosive characteristics. Potential candidate explosions are confirmed by examination of the raw waveform data. Using this procedure, we have identified hundreds of explosions throughout the Indian Ocean Basin. The instigators of the explosions are not known, but the locations and characteristics of the explosions lend themselves to likely candidates. These include military exercises, construction, geophysical exploration, and local fishing practices. We examined hydroacoustic data covering a 6-year period and identified 305 separate explosions. Of these, 25 were recorded at three hydrophone triads - Cape Leeuwin, Australia (H01W), Crozet Island (H04N) and Diego Garcia (H08S) - 79 were recorded at two triads - H04N and H08S - and 201 were recorded at a single triad. In addition, we have observed many airgun surveys, but they are not of interest here due to their local nature. We are able to locate explosions observed at three or two triads using direct arrivals. In some cases, we can locate explosions recorded at a single triad using observed reflections. Absolute arrival times can be estimated to less than 2 seconds, and relative times for closely spaced explosions can often be estimated to within a few samples (4 to 12 milliseconds). Backazimuth uncertainty estimates range from a few tenths of a degree to several degrees depending on the frequency content of the signal and noise conditions at the triad. The explosions are distributed in three general locations: the Arabian Sea off northwestern India, the Bay of Bengal, and along the islands of western Indonesia.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA519370
Entities
People
- Colin L. Reasoner
- J. R. Bowman
- Jeffrey A. Hanson
Organizations
- Leidos