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| Title: | Acoustic propagation by bottom bounce mode to the north west of Australia |
| Report number: | DSTO-TR-0198 |
| AR number: | AR-009-325 |
| Classification: | UNCLASSIFIED |
| Report type: | Technical Report |
| Authors: | Lawrence, M.W.
Prenc, S. |
| Issue Date: | 1995-07 |
| Division: | Maritime Operations Division |
| Abbreviation: | MOD |
| Release authority: | Chief, Maritime Operations Division |
| Release limitations: | PUBLIC RELEASE |
| Announce limitations: | Public Announce |
| Task sponsor: | DSTO |
| Task number: | DST 88/232 |
| File number: | 510/207/0132 |
| Pages or format: | 117 |
| References: | 26 |
| DSTORL/DEFTEST terms: | Bottom bounce
Acoustic propagation
Sea floor
Bottom loss
Sonobuoys |
| Other descriptors: | Sonar effectiveness |
| Abstract: | Underwater acoustic propagation measurements have been made in deep water to the north west of Australia, in the Indian Ocean. The resulting sets have been analysed to provide acoustic bottom loss as function of frequency and grazing angle for the 23 sites investigated. The experiments and the analysis are described, together with the results. Good information is available on the geology of the sites of the propagation runs. A comparison is made of the data between the various sites. |
| Executive summary: | Understanding the effectiveness of sonar systems is essential for assessing their operation in pro- or anti- submarine warfare. Sonar performance varies from one
ocean environment to another, with large variations in detection range resulting from differences in acoustic propagation conditions. In most instances the factor which has the largest effect on long-range propagation is the sea floor. This factor also has the largest variability from one location to another. Understanding and prediction of the interaction of acoustic energy with the sea floor is complicated by the penetration of the energy into the sediments and rocks that make up the sea floor.
This report describes a series of measurements of the effect of the sea floor on acoustid propagation. These measurements have been performed to characterise the acoustic sea floor interaction as an acoustic bottom loss (that is the energy loss on a single interaction). The bottom loss (expressed in decibels) is measured for acoustic energy at each of a range of angles of incidence with the sea floor. Other properties of the sea floor at the measurement sites are also obtained, both by measurement and from published results. These other properties are useful in establishing relationships between the acoustic results and the nature of the sea floor.
This report covers measurements of acoustic bottom loss to the north-west of Australia, in the Indian Ocean. Earlier reports covered the regions to the east and
north-east of Australia.
Each set of acoustic propagation measurements reported here was made from a ship (HMAS Cook) which dropped a sonobuoy, and whilst steaming away, dropped
explosive charges at regular intervals. The acoustic signal received by the sonobuoy was recorded and relevant sections were analysed. Bottom loss values have been calculated from these measured acoustic signals.
The work reported here is the only existing published data set on bottom loss in deep water in this region. Unpublished results do exist but are limited in their range of
frequencies and grazing angles. In the work reported here, in conjunction with the acoustic results, there is also an accurate set of relevant environmental data at each site, which is useful for further analysis of the results. The sigruficant variability of bottom loss results, even for the same geoacoustic province, is once again demonstrated.
The purpose of the measurements of bottom loss reported here is to help characterise the effect of the sea floor on acoustic propagation in areas of direct military
interest to Australia. The sea floor frequently plays a very sigruficant role in determining the sonar effectiveness for pro- or anti-submarine warfare. Better characterisation of the sea floor allows improved sonar modelling and detection-range prediction. |
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