NOAA Teacher at Sea
Aboard NOAA Ship Okeanos Explorer
July 12 – 31, 2018
Mission: Mapping Deep-Water Areas Southeast of Bermuda in Support of the Galway Statement on Atlantic Ocean Cooperation
Geographic Area: Atlantic Ocean, south of Bermuda
Date: July 12, 2018
Weather Data from the Okeanos Explorer Bridge – July 12, 2018
Air Temperature: 26.2°C
Wind Speed: 10.7 knots
Depth: 693 meters
Science and Technology Log
According to the Oceanic Institute, the oceans cover 71% of the Earth’s surface. This is calculated to be 335,258,000 square kilometers! Recently, the Okeanos Explorer mapped over 1,000,000 square kilometers of the seafloor using high- resolution multibeam sonar. Although this may not seem like much, that region is larger than the areas of Arizona and Texas combined!
So why is it so important for the Okeanos Explorer to map the seafloor? The ocean’s terrain plays a very important role in ecosystems since underwater valleys determine currents and weather patterns, sea topography influences fishery management, and seamounts serve as protection against unpredictable storms. Therefore, high-resolution maps allow scientists to categorize marine habitats, provide information vital to protecting and tracking marine life, and enable us to make smart decisions for solid, sustainable conservation measures.
In order to successfully map the ocean floor, multibeam sonar is used. The Okeanos Explorer uses an EM 302 multibeam system that is designed to map a large portion of the ocean floor with exceptional resolution and accuracy. The EM 302 transducers point at different angles on both sides of the ship to create a swath of signals. Transducers are underwater speakers that are responsible for sending an acoustic pulse (known as a ping) into the water. If the seafloor or object is in the path of the ping, then sound bounces off the object and returns an echo to the transducer. The EM 302 has the ability to produce up to 864 depth soundings in a single ping. The time interval between the actual signal transmission and arrival of the return echo (two way travel time) are combined with a sound velocity profile to estimate depth over the area of the swath. In addition, the intensity of the return echo can be used to infer bottom characteristics that can be utilized for habitat mapping. Since the EM 302 creates high density, high-resolution data as well as water column features, this sonar system is ideal for exploring the seabed for geographic features.
The image below shows data being collected by the multibeam sonar on the Okeanos Explorer. The colors are used to indicate swath depth (warm colors indicate shallow waters while cool colors indicate deeper waters).
As this data is being collected, it must be “cleaned” to eliminate any erroneous points. Data is collected and cleaned in both the Dry Lab and Mission Control Room.
Since we have not reached the survey area yet, we have been monitoring the depth of our path thus far. We are collecting transit data which is considered to still be valuable data for unmapped seafloor area, but it may not be as high quality as focused mapping data. We will continue to collect transit data until we reach the survey area near Bermuda.
Life onboard the Okeanos Explorer has been a very interesting and fun learning experience! The ship runs on a 24/7 operation schedule and people are working diligently at all hours of the day. Everyone on the ship has been really welcoming and willing to share their stories and insights about their careers at sea. I am really looking forward to speaking with more people to learn about their experiences!
We set sail out of Norfolk today and began our 3.5 day/4 day transit to the survey area near Bermuda. This morning, we found out that we will need to schedule an emergency dry dock towards the end of our mission to solve an issue with a stern thruster necessary for ROV cruises. As a result, we will not be ending up in port in St. George, but we will still be able to map the area 200 nautical miles off the coast of Bermuda, so that is great!
Did You Know?
Sonar is short for Sound Navigation and Ranging.
Check out this video for a visual representation of the process sonar uses to generate data! https://oceanservice.noaa.gov/caribbean-mapping/mapping-video.html