Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
Gray's Reef Expedition 2012
Mission Information
 

Sunday: May 20, 2012
Log Day 6

Kacey Johnson
BS Geology / College of Charleston

Kacey Johnson (l) and Samantha Martin (r) prepare to deploy the CTD unit

Kacey Johnson (l) and Samantha Martin (r) prepare to deploy the CTD unit.
(Photo: Debbie Meeks)

As a volunteer scientist aboard the NOAA Ship Nancy Foster my duty under the guidance of the Senior Survey Technician, Samantha Martin, is to watch the Reson 7125 multibeam sonar system from the ship's Dry Lab (computer lab) to make sure survey acquisition is running smoothly. Also, we deploy CTD casts at intervals of approximately every four hours. CTD stands for Conductivity, Temperature, and Depth (i.e., pressure) and is deployed off the side of the ship and down to within a few meters of the seafloor to capture an SVP (Sound Velocity Profile). The three parameters captured by the CTD cast of conductivity, temperature, and depth have a profound effect on the speed of sound throughout the water column.

Kacey Johnson (l) and Samantha Margin (r) connecting cable to 
         download the CTD data

Kacey Johnson (l) and Samantha Martin (r) connecting cable to download the CTD data
(Photo: Debbie Meeks)

After each survey line is run, I bring the raw multibeam data into Caris HIPS and SIPS to process the data and apply SVP, tide, and ship position offsets in order to produce an accurate representation of the seafloor. Additionally, I generate backscatter using Geocoder algorithms in Caris HIPS and SIPS to produce a map of varying sonar signal intensities.

Kacey Johnson in dry lab with bathymetry and backscatter images

Kacey Johnson in dry lab with bathymetry and backscatter images.
(Photo: Debbie Meeks)

Backscatter measures the intensity of sound waves reflected back to the sonar receiver after hitting the seafloor. For example, sand and mud absorbs sound waves so the intensity of sound reflected off of sand or mud would be quite weak compared to sound waves reflected off of denser rocks like limestone. Backscatter is important because scientists need to know what the geology of the seafloor is so they can determine what types of habitats can be found there.

Kacey Johnson in dry lab with survey acquisition computers

Kacey Johnson in dry lab with survey acquisition computers
(Photo: Debbie Meeks)

On this cruise, I am interested in finding hard bottom habitats because these habitats are important to spawning fish, coral, and other marine fauna. I would know where to advise scientists to consider diving to find hard or live bottom habitats by (1) examining backscatter maps for areas of high signal intensity, and (2) by looking at the bathymetry for areas of high relief. Then, divers can groudtruth these locations so these important marine habitats can be protected from overfishing, bottom trawling, and other harmful activities.

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