| Popis: |
Recent experimental and theoretical works in ultrasonics show that the Green’s function between transducers fastened to an aluminum sample can be measured from the correlation of thermal noise [R. L. Weaver and O. J. Lobkis, ‘‘Ultrasonics without a source. Thermal fluctuation correlations at MHz frequencies,’’ Phys. Rev. Lett. 87, 134301 (2001)]. Similar results have been obtained in geophysics using seismic noise data [A. Paul and M. Campillo, ‘‘Extracting the Green’s function between two stations from coda waves,’’ Trans. Am. Geophys. Union 82–47, F842 (2001)]. Sources of noise in underwater acoustics range from ship noise at low frequency to surface noise and even thermal noise at very high frequencies. We theoretically demonstrate that at least an approximate Green’s function can be obtained from surface noise. This result is confirmed by noise data recorded on arrays of receivers during the NPAL98 experiment. [Work supported by ONR.] a)The NPAL group is composed of J. A. Colosi, B. D. Cornuelle, B. D. Dushaw, M. A. Dzieciuch, B. M. Howe, J. A. Mercer, R. C. Spindel, and P. F. Worcester. |
