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Zimmerman, R, D'Spain GL, Chadwell CD.  2005.  Decreasing the radiated acoustic and vibration noise of a mid-size AUV. Ieee Journal of Oceanic Engineering. 30:179-187.   10.1109/joe.2004.836996   AbstractWebsite

An Odyssey IIb autonomous underwater vehicle (AUV) made by Bluefin Robotics, Inc., was acquired by the Marine Physical Laboratory Scripps Institution of Oceanography, to conduct research in underwater acoustics as well as provide a platform for other scientific studies. The original Odyssey IIb tail cone was replaced with a ducted fan, vectored thrust system installed on vehicles currently sold by Bluefin. In initial sea tests with the new thrust system, the acoustic self noise levels of the vehicle while underway were 20 to 50 dB higher than typical ocean background noise levels, preventing the vehicle's use as a receiver of low level sounds. Controlled tests were performed to characterize the radiated and vibration noise of the AUV propulsion and actuators. Once this baseline was established, changes were made, mostly to the tail cone propulsion, to decrease the vehicle's self noise. The resulting self noise levels of the AUV from 10 Hz up to 10 kHz measured while underway by a hydrophone mounted on the AUV's inner shroud now are at or below typical shallow water background noise levels except in three bands; below 250 Hz, around 500 Hz, and from 0.9 to 2.0 kHz. The goal of this paper is to describe these changes and their effects in lowering vehicle noise levels.

Chadwell, D, Spiess F, Hildebrand J, Young L, Purcell, George J, Dragert H.  1998.  Deep-sea geodesy; monitoring the ocean floor. GPS World. 9:44-50,52-55., Eugene, OR, United States (USA): Aster Pub. Corp., Eugene, OR AbstractWebsite
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Osada, Y, Fujimoto H, Kanazawa T, Nakao S, Sakai S, Miura S, Hildebrand J, Chadwell CD.  2006.  Development of a GPS/acoustic seafloor positioning system for 6,000 m water depth and its trial experiments at sea. Journal of the geodetic Society of Japan. 52:171-182. Abstract
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Chadwell, CD, Bock Y.  2001.  Direct estimation of absolute precipitable water in oceanic regions by GPS tracking of a coastal buoy. Geophysical Research Letters. 28:3701-3704.   10.1029/2001gl013280   AbstractWebsite

A buoy-based CPS receiver and meteorological sensor are used to estimate directly the absolute precipitable water (PW) overlying a coastal ocean site 8 km from shore. During an 11-day experiment, one-second CPS data collected at the buoy and at a shore station are combined with 30-second data from four distant CPS stations to estimate the buoy position, zenith wet delay, phase biases, and receiver and satellite clocks using double-differenced phase processing with ambiguity resolution. GPS-derived PW at the buoy compared to radiosonde measurements (20) and to half-hourly GPS-PW values (384) from the nearby shore station show an rms agreement of +/-1.5 mm and +/-1.8 mm, respectively. Hourly means (170) of the GPS-measured vertical motion of the buoy show a +/- 24 mm rms agreement with a NOAA tide gauge, equivalent to about 4 mm of PW. GPS-derived PW from buoys may have the potential to improve weather forecasting, calibration of satellite-based sensors, and climate studies.