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August 11, 2002 (day 223), 5:36 UT
A signal from a RAFOS sonic beacon, sweeping from 259 Hz to 261 Hz in 80 seconds. This signal was broadcast at exactly 5:30 UT. The propagation delay is used by drifting instrumentation packages to determine their position. (See NPS pages for details.) (The lines going clear across the spectrogram are electronic artifacts, not ocean sounds.) |