Figure 3. An example pressure waveform for a typical bucket deployment and retrieval cycle

ERDC TN-DOER-E14

August 2001

As described, the six sound events are repeated on approximately a 1-min period with minor (e.g.,

10-15 sec) variations. Occasional interruptions in the cycles occurred to accommodate barge

maneuvering, dumping and washing activities, and equipment maintenance. Figure 3 illustrates a

complete cycle encompassing these events for the dredge Viking.

Figure 3. An example pressure waveform for a typical bucket deployment and retrieval cycle

Based upon the six-event sequence, initial data analyses focused only on these six distinct dredge

cycle sounds as captured in Viking recording sessions 3-9 and 11-15. Session 4 was excluded from

this analysis because a tug and barge not related to the dredging operations transited the listening

position during almost the entire recording session, thus masking dredge-induced sounds. Session 12

was also excluded from further analysis because no noises characterizing the Viking dredging

activity were audible at that range above the distant background noise created by barge washing

operations from the Crystal Gayle dredge operations near the listening positions. Session 13 was

conducted at an approximate distance of 7 km from the dredge. Only faint sounds associated with

bucket impact on the bottom were audible at this range. Because the remaining sound events of the

dredge cycle were indistinguishable at this distance, session 13 was excluded from further analysis.

As previously stated, during the recording sessions, field notes including distance to the dredge or

other sound sources were recorded simultaneously on the right channel of the DAT tape. At close

ranges the distance was obtained with a laser rangefinder and the distance recorded in meters. When

the distance was further than the maximum usable distance for the laser rangefinder (approximately

500 m), the radar unit aboard the Margaret M was used and estimated distances were recorded as

nautical miles. All distances recorded in nautical miles from the radar were converted to meters,

and the estimated distance to the dredge was then interpolated based on recording times, distance

notes, and times at known audible events.