First release: 2015
Revised: July 2017 (ver. 2.0)
Approximately 95 square kilometers of area was mapped with multibeam sonar. The survey expanded the extent of mapping data collected by Solmar Hydro Inc. in 2013 under a contract with WindFloat Pacific. When added to the Solmar Hydro data the total area mapped is approximately 140 square kilometers, lying in Federal waters on the shelf offshore of Coos Bay of interest for renewable energy (OCS-P lease blocks 6523, 6524, 6573, 6574, 6623, 6624, 6673, and 6674). Water depths range from 300 to 500 meters and are within the effective depth range of the Reson 7111. The seabed in his area is composed of sand and mud, with rocky outcrops on tectonically uplifted features. The survey was conducted using 12 hour day operations out of Charleston Harbor near Coos Bay, Oregon. The cruise plan consisted of 23 days on site split between sonar mapping and video ground truth surveying. Activities parsed out to nine days of sonar mapping, three days of video surveying, eight days of no operations due to weather, and three days mobilizing and demobilizing. Typically the Snavely would transit out to the survey area in an hour at a speed of 20 knots. Multibeam sonar operations were conducted on north or south oriented tracklines at a speed of 4 to 5 knots depending on sea state. The optimal heading for sonar operations is isobath parallel. Video operations were conducted by deploying up drift of a target and drifting over it at speeds of 1 knot or less. Mammal observations were made during multibeam operations. The USGS voluntarily staffs its seismic and sonar ships with a trained mammal observer for seismic and sonar operations in Federal waters. The observer monitored the survey area for 30 minutes prior to the start up of the sonar system to ensure that no marine mammals were in the area. The observer called for system shut downs when marine mammals entered the 160dB isopleth (safety zone). Whenever a marine mammal entered the safety zone the sound source was shut down until it was confirmed that the marine mammal had either left the safety zone, 15 minutes had passed after its last sighting, or the vessel transited to another trackline. The Reson 7111 multibeam sonar operates at a frequency of 213.5 kHz and has a peak source level of 213 db. The radius of the safety zone for the Reson 711 is 200 m. The second half of the cruise was devoted to ground truth video surveying. The video survey was designed after the sonar mapping to investigate sea floor features of interest. Features of interest include bathymetric features such as ridges and depressions, areas that represent the spectrum of backscatter intensity observed in the survey area, and areas that represent the spectrum of water depths surveyed. The camera sled has downward and adjustable oblique-forward facing HD video cameras. A fiber optic cable is used to allow real time on board viewing of both camera feeds. There is a forward scanning sonar for collision avoidance. Conductivity and temperature are continuously recorded using a SeaBird Seacat 37-SM. Depth and altitude are measured to aid operations but not recorded. There is a downward facing still camera for small invertebrate identification but lighting was insufficient on this new camera sled for usable still images. Observations of the major and minor substrate type are made as well as occasional comments about organisms, features, or objects of interest. There were 18 video transects; 11.6 hours of video were collected; the mean length of time per transect was 38 minutes. A CMECS habitat map will be published following analysis of the data.
