Heather O’Connell: Understanding Hydrographic Surveying and Life on a Ship, June 4, 2018

NOAA Teacher at Sea

Heather O’Connell

NOAA Ship Rainier

June 7 – 21, 2018

Mission: Hydrographic Survey

Geographic Area of Cruise: Seattle, Washington to North Coast of Kodiak Island, Alaska

Date: June 4, 2018

Weather Data from the Bridge

This evening as I write the blog in port in Seattle, Washington, it is partly cloudy with a low of 53 degrees Fahrenheit. There are west southwest winds at 10-14 miles per hour.

Science and Technology Log

NOAA Ship Rainier surveyed parts of Possession Sound last month and survey technicians created two and three dimensional maps with the depths of the sea floor around Everett, Washington. The 31 square nautical mile maps were developed after processing data utilizing single-beam and multi-beam sonar over a three week period. A colored depth range map was generated and superimposed onto a previous nautical map. The fact that the contour lines matched proved the accuracy of the survey. An exciting part of the Puget Sound survey proved to be a shipwreck from an Alaskan fishing boat that burned when anchored in 1982. 

Color map generated on top of previous nautical map
Color map generated on top of previous nautical map

Before completing the survey, a computer-generated polygon plan was drawn to section out the areas that each boat would cover. While Rainier has the ability to survey large areas, it was out of the water being repaired due to damage to the rudder. The four launch boats and one small shoreline ship covered the entire area. The launch boats utilized an efficient multi-beam sonar to generate the map in conjunction with a single beam sonar on a shoreline ship. The single beam sonar is located on a jet boat, rather than a boat with a propeller, which has less draft, making it a better platform for surveying in shallow water. 

Multi-beam sonar has the ability to quickly and accurately collect data on the depth of the sea floor. NOAA Ship Rainier and the four launches each have a multi-beam sonar where the transmitter sends out a sound pulse and the receiver creates a 512 beam from the returning echo of the sea floor.  The 512 beam swath, or fan shaped area of sound beams, generated from the receiver creates an image on the computer of the depth of the sea floor. The sound travels to the ocean floor and then back to the receiver in the boat, located perpendicular to the transmitter in a Mills Cross orientation. The time return, or time it takes to send out a signal and return to the receiver is then applied to an algorithm that determines the depth of the ocean floor. Things to consider in the speed of sound include the source level of the sound, the transmission loss from the sound traveling, and the noise level from other materials. Further factors that affect sound travel in the ocean include the type of sediment. Soft sediment like mud and silt absorb sound while hard materials like rock, granite and metal reflect sound energy. The tides must also be recorded and utilized to determine the actual depth of the water. All of these factors are put into the formula used for calculating sea depth.

A multi-beam sonar in the Mills Cross orientation on the underside of a launch boat
A multi-beam sonar in the Mills Cross orientation on the underside of a launch boat

Collecting data in deeper water is easier than surveying shore-line data. The near-shore data uses single resolution for more detail and the outer depth information utilizes a much higher resolution, or coarse resolution. The combined variable resolution allows for the multiple resolution image to be put on one surface, generating specific maps. Shoreline surveys have a narrow swath meaning there are closer runs that must go back and forth in order to cover the same range as a deep water survey. The multi-beam swath may only reach 8 meters when close to shore, but may be as wide as 60 meters when it can travel further into the ocean. So shallow water takes longer to survey and deeper water can be surveyed faster.

Once all of the data is collected, the points from the beam become pixels on a two dimensional or three dimensional computer generated map.  The time return charts are put into the Caris software, which is like the arc GIS of nautical maps. The software produces a map with varying depths of the ocean floor represented by different colors. Hydrographic Survey technician Amanda generated this accurate 3-D image of the shipwreck around Everett after processing the data.

Boat Wreck
Pings from multi-beam sonar become pixels in this 3-D image of the boat wreck in Possession Sound

Survey technician Amanda also shared her knowledge on removing the noise from images before generating maps. Often times, the sonar waves create some interference that doesn’t match up with the rest of the map and must be removed. Different ships survey the data using different colors so that when the maps are combined, the differences are apparent. The role of processing data is completed by survey technicians during the off season or when the ship is not actively surveying, such as when it is in port. Technicians have a one hundred and twenty day time period to complete data processing to the established specifications post survey. Data is then sent to the Pacific Hydrographic Branch for quality control and eventual submission to the Marine Chart Division for eventual application to nautical charts. 

Personal Log

I arrived early morning on Saturday, June 2nd and after taking a taxi to the Seattle Coast Guard base, a patrolling officer brought me to Ship Rainier. I called the bridge and informed the officer on watch that I had arrived. Charlene, the A.B., or able bodied seaman, was on watch and gave me a basic tour, although I only assimilated a small portion with my sleep-deprived, jet-lagged brain. Luckily, I had haphazardly met my roommate. She showed me the tight sleeping quarters with locking drawers and cabinets to keep all things stationery, along with a small sink in the corner. The bunk consisted of two metal beds stacked on top of each other with only enough room to lay down. Since there are only two of us staying in the room for four, it is reasonably comfortable. There are two bathrooms, or heads, along with two showers located in the hall outside of bunk C-09.

After resting for quite some time, I joined Audrey and Mike, two hydrographic survey technicians, on an adventure to Pike’s Marketplace on this atypically warm Seattle afternoon. Open faced crab and wild salmon sandwiches were enjoyed overlooking the Puget Sound and the bustling market. Exploring downtown Seattle on foot proved to be a graceful way to transition to this new way of life at the port.

Pike’s Marketplace in Seattle

On Sunday, I went for lunch with Dan and Johnny from the engineering department. These two were working hard to cut a metal plate on the stack so that they could access inside for repairs. Preparing to embark on a ship for a week in transit requires tremendous work. I have thoroughly enjoyed observing the process for this journey and look forward to leaving the port when the time comes.

Not only do I enjoy living on a ship at port, but I love learning about the different lifestyle of the Rainier crew. Some long term ship employees have Ship Rainier as their address and reside in Newport, Oregon on this ship during the off season during the winter. Oftentimes, they are out to sea for three weeks at a time during the field season, then they port for several weeks.

Today was the first day a meal was served on the ship and I came across several familiar and new faces at breakfast. After breakfast I went to the prop room and the holodeck where the officers and technicians were analyzing data. At 1300 there was an all hands meeting with an update from the Captain and Chief Officer or CO. Next, I received damage control, or D.C., from Michelle Levano who also grew up on Long Island, New York. The training included two other new junior officers, Stephanie and Harper, who studied Environmental Conservation and Aeronautical Engineering, respectively. Christopher, a new A.B. and Ray from engineering also joined us on the walk around the ship where we learned the different signals for various emergencies that might take place on the ship. I also learned where the lifeboats are located and the protocol for a man overboard, M.O.B.,or what to do if and when you have to abandon the ship.

So, all in all my time on the ship and in Seattle has had a balance between the new structure of life on a ship with the freedom to explore a city. I’m excited to experience how Rainier functions once we leave the port life on Thursday at 1300 hours. I’m also curious what it will be like to be stationed to a 231 foot vessel when I’m used to the freedom of exploring.

Sunset from the Seattle Coast Guard Base

Did you know?

There are two types of NOAA employees on ship Rainier. There are NOAA employees and also NOAA Commissioned Officer Corps employees who wear uniforms and operate like U.S. military officers. They share the uniform of Coast Guard members and are one of the two unarmed branches of the military.


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