Title

Arctic Sound Speed: A Desktop Study for Single Beam Echo Sounding

Abstract

The Seafloor Sounding in Polar and Remote Areas (SSPARR) buoy is an autonomous echo sounding buoy envisioned for deployment in polar waters, in which ice cover and inclement weather frequently prevent normal shipboard survey operations. The buoy includes an echo sounder, a GPS, and Iridium phone sub- systems, allowing system to periodically fix its position, sound for the local water depth and telemeter the data to shore. The measurement of an echo sounder is the two-way travel time of a transmitted pulse. In order to obtain the approximate depth, the one-way travel time is multiplied by the vertical harmonic mean sound speed depth. However, as the local sound speed profile is not measured by the buoy, a suitable profile must be derived from another source. An analysis of 19,795 conductivity-temperature-depth (CTD) vertical measurement profiles taken between 1972 and 2003 in the Arctic Ocean (above 65N Latitude) has been conducted to determine the variability of sound speed as a function of depth throughout the Arctic (World Ocean Database 2005, NODC). The temperature stability provided by the freezing point of water creates an environment such that a single canonical sound speed profile is sufficient for single beam echo sounding for the entire Arctic. Upper and lower sound speed values within each 1-meter depth interval are used to bound the likely error of depth soundings measured using the canonical profile. The method is compared to the traditional method of using historical tables (Carter's Tables) to correct echo sounders operating at a nominal (4800 ft/sec [~1463 m/s]) sound speed, and found to reduce sounding errors as much as 4%.

Publication Date

12-2008

Journal or Conference Title

American Geophysical Union (AGU)

Volume

89

Conference Date

Dec 15 - Dec 19, 2008

Publisher Place

San Francisco, CA, USA

Publisher

American Geophysical Union Publications

Document Type

Conference Proceeding

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