Previous Front Pages


Shipping noise is an important part of the ocean 'environment', and presents interesting modeling problems. The Philippines Sea is chosen as an example of a moderate sized ocean basin for the calculation of noise directionality. The upper left shows the elevation with the color bar giving negative elevations in meters. Green is also used for land. Shipping noise source level densities, at 50 Hz, are plotted in the upper right and are indicative of shipping lanes. The colors represent dB re: 1 microPa2 /Hz @ 1m/m2. A virtual receiving array is located in the center of the basin. The calculated noise directivity is plotted versus bearing and elevation angle for a hard (reflective) ocean bottom, and for a soft (absorptive) bottom. Energy from near surface sources, over slopes, is seen in a range of elevation angles, around zero degrees. Differences between the two cases clearly show the importance of the ocean bottom reflectivity.


ONR's BASSEX program is studying the acoustic shadows cast by seamounts. The example above shows the bathymetry, along with measured TL for a recent test near the Kermit-Roosevelt seamount in the North Pacific. The strong shadowing effects are clearly visible. Three-dimensional acoustic models (lower panels) are being validated using a benchmark problem with a conical seamount.


Crossword puzzle

Click on the above figure to complete the Ocean Acoustics crossword puzzle or click here to download a PDF of same. Happy Holidays!.


The wireless internet extends to the sea .... ONR's research in high-frequency acoustic propagation and acoustic communications is providing the underlying science that will enable flexible undersea networking. A prototype system shown above has been developed in the navy's SeaWEB program. The network is being used for real-time oceanographic observations in the FRONT program.


Possible applications of time-reversal acoustics are being studied by several groups. A transmitted signal is received on the vertical array on the right as a complicated waveform. However, when that received waveform is back-propagated, a focused signal is received back at the source.