Documents in the NTIS Technical Reports collection are the results of federally funded research. They are directly submitted to or collected by NTIS from Federal agencies for permanent accessibility to industry, academia and the public.  Before purchasing from NTIS, you may want to check for free access from (1) the issuing organization's website; (2) the U.S. Government Printing Office's Federal Digital System website http://www.gpo.gov/fdsys; (3) the federal government Internet portal USA.gov; or (4) a web search conducted using a commercial search engine such as http://www.google.com.
Accession Number ADA574833
Title Normal Mode Properties and Signal Coherence in Shallow Water Propagation.
Publication Date Sep 2012
Media Count 4p
Personal Author H. A. DeFerrari
Abstract For many years, the 6.1 basic research communities have focused on the effects of internal waves on temporal coherence; whereas, Navy applied programs are more concerned with the randomizing effect of the combination of bottom bathymetry variations and platform motion on array (spatial) coherence. We find that it is not possible to isolate these two causes in the shallow ocean. In the deep ocean and for propagation by refracted paths, one need only consider the effects of internal waves to understand coherence. But in shallow oceans, propagation is generally by reflected paths and bottom variability can and does affect coherence and often is more randomizing that internal waves. We have found that for very low frequencies the bottom bathymetry variation are a small fraction of the acoustic wavelength and the bottom appears flat and internal waves alone determine coherence. At very high frequencies the bottom variations are a large fraction of the wavelength and so even the slightest sound speed variations randomize and de-correlate the signal even without internal waves. But for the practical mid-frequency range, (400Hz to 3kHz), the effects of each cause are interwoven and generally inseparable. For many years, the 6.1 basic research communities have focused on the effects of internal waves on temporal coherence; whereas, Navy applied programs are more concerned with the randomizing effect of the combination of bottom bathymetry variations and platform motion on array (spatial) coherence. We find that it is not possible to isolate these two causes in the shallow ocean. In the deep ocean and for propagation by refracted paths, one need only consider the effects of internal waves to understand coherence. But in shallow oceans, propagation is generally by reflected paths and bottom variability can and does affect coherence and often is more randomizing that internal waves.
Keywords Acoustic signals
Approximation(Mathematics)
Bathymetry
Coherence
Ray theory
Shallow water

 
Source Agency Non Paid ADAS
NTIS Subject Category 48G - Hydrology & Limnology
46A - Acoustics
Corporate Author Miami Univ., FL. Inst. of Marine and Atmospheric Sciences.
Document Type Technical report
Title Note Annual rept.
NTIS Issue Number 1318
Contract Number N/A

Science and Technology Highlights

See a sampling of the latest scientific, technical and engineering information from NTIS in the NTIS Technical Reports Newsletter

Acrobat Reader Mobile    Acrobat Reader