Executive Summary
Conclusions
Presentation given at the 2014 INMARTECH Meeting in Corvallis, Oregon in November, 2014.
Highlights:
Typical Sources of Acoustic Noise:
Why Acoustic Noise is Important:
Gates Acoustic Services was tasked by SCRIPPS Institute of Oceanography to investigate and quantify acoustic issues associated with operation of the USCGC HEALY (WAGBG20). An at-sea investigation was accomplished during ship operations in deep water out of Nome, Alaska on August 13-24, 2014.
Gates Acoustic Services was tasked by University of Alaska, Fairbanks, to investigate and quantify acoustic issues associated with operation of the R/V SIKULIAQ. An at-sea investigation was accomplished during ship operations in deep water out of San Juan, Puerto Rico on September 12-18, 2014.
KILO MOANA’s acoustic signature was higher than previous acoustical data due to electronic noise interference. The levels in the EM 122 sonar operational frequency of 12 kHz were also higher than historic data. A significant problem was noted with numerous elements of the EM 122 sonar array that is believed to be associated with electronic background noise. Electronic noise was determined to be the major deficiency during this acoustic trial.
KILO MOANA’s acoustic signature was comparable to previous acoustical data with one noted exception. The levels in the EM 122 sonar operational frequency of 12 kHz were similar to historic data. A new problem was discovered that was associated with engine and switching room air handler cooling systems. This problem created 4,000 Hz harmonics from the fundamental up through 80 kHz (the limit of onboard instrumentation). An additional problem was noted with numerous elements of the EM 122 sonar array that is believed to be associated with electronic background noise.
R/V MELVILLE acoustic signature was successfully measured during this acoustic test. The levels of the EM 122 were controlled by a combination of propeller and anti-roll tank transients.
The general acoustic levels of MELVILLE were good and should produce excellent bathymetric data results:
The acoustic signature of R/V ATLANTIS was successfully measured during this acoustic test. The levels of the EM 122 were controlled by a combination of flow noise and gondola cavitation. Higher sea state data was also influenced by bubble sweepdown effects.
The general acoustic levels of ATLANTIS with the new gondola mounted EM 122 sonar system were good and should produce excellent bathymetric data results:
R/V MARCUS G. LANGSETH’s acoustic signature was successfully measured during this acoustic test. The levels of the EM 122 were controlled by propeller cavitation. The quietest vessel condition/speed was when the controllable pitch propellers were set to 85 percent pitch with an engine speed of 600 RPM. This yielded a ship speed of 10 knots and a sonar level of 52 dB. The seismic system created high levels when it was operating.