| Autor: |
Burenkov, S. V., Gavrilov, A. N., Uporin, A. Y., Furduev, A. V. |
| Zdroj: |
Journal of the Acoustical Society of America; 1991, Vol. 90 Issue 4, p2330-2331, 2p |
| Abstrakt: |
On 26-31 January 1991, the ''Akademik Nikolai Andreev'' research vessel anchored at Krylov underwater mountain (17.5° north, 30° west) received the low-frequency signals at a distance of 12.5 thousands kilometers from the source disposed at Heard Island. All transmitted signals were received by two omnidirectional hydrophones at the SOFAR axis and 200-m depth, sampled, and collected on the cartridge tapes by the data acquisition system. All three types of signals-continuous wave 57 Hz, pentaline, and phase coded (M sequence)-have been primarily processed in the time and frequency domains. The purposes of data processing were to determine what the intensity of signals are, the signal/noise (S/N) ratio and temporal variation of the signal phase and magnitude, what is the time structure of the multimode signal, and how time stable is this structure. On most of the transmissions the S/N ratio was about 10-15 dB in 1-Hz band at the carrier frequency 57 Hz, and then it decreased to 0-5 dB on last transmissions. Both temporal variation of Doppler shift and phase fluctuation dominantly depended on the nonuniformity of ship's motion. GPS data of both ships were compared with the phase variance of some received signals. The distinction between GPS and phase estimations of distance variance is about 10-15 m on an average. The cross-correlation processing of the phase-coded signal enabled one to identify the periodical groups of pulse arrivals that follow with the period of transmitted M sequence. The time stability of multipath arrivals was 5 min and less. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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