Tag: seafloor mapping

NOAA Teacher at Sea
Christy Garvin
Onboard NOAA Ship Rainier
June 1 – 8, 2005

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, AK
Date: June 7, 2005

Weather from the Bridge

Latitude:56 deg 59 min N
Longitude: 135 deg 17 min W
Visibility: 11 nautical miles
Wind Direction: 290 deg
Wind Speed: 10 kts
Sea Wave Height: 0-1 ft
Sea Water Temperature: 50deg F
Sea Level Pressure: 1011.7 mb

Science and Technology Log 

Although we have been parked in protected Aleutkina Bay for most of the leg, yesterday afternoon we pulled anchor and the ship was underway.  Because of weather conditions, it was determined that the ship would run hydro in deep water, while the launches continued protected shoreline work.

The ship is equipped with a Seabeam 1050 MKII; it is a dual frequency echosounder with 50KHz and 180KHz operating frequency. When operating at the 180 KHz frequency a maximum depth of 620 meters can be surveyed.  This depth can be increased by switching to the 50 KHz frequency, which can reach depths of 3,100 meters.  The Seabeam 1050 has a wide horizontal scan area that is covered by 126 adjacent beams and a 150-degree swath width; it has high resolution due to the narrow beams it uses.

While the ship is doing hydro, the crew transitions into 24-7 watches.  The ship runs survey lines all night, so people are needed to steer the ship, serve as lookouts, and run the survey equipment.  The watches are four hours each, and crewmembers work two watches a day. The three shifts are 12:00-4:00, 4:00-8:00, and 8:00-12:00; people are sleeping at different times, so everyone makes an effort to be quiet during the day.

One of the highlights of today was an in-depth tour of the ship by the CO, John Humphrey.  I was able to see the engine room with the two main engines, the after steerage (where the rudder and emergency steering are located), and the evaporator unit that processes salt water into potable fresh water.  We also went into the large refrigerators and freezers that hold the ship’s stores and climbed down into the bowels of the ship to see the fire prevention carbon dioxide system.

Personal Log 

It is interesting trying to sleep while the ship is underway. Although the seas aren’t very rough, the ship still moves quite a bit.  I haven’t been seasick (I’m very thankful for that), but I rolled all over my bunk last night.  It felt like I was trying to hold myself in the bed as I slept.

NOAA Teacher at Sea
Christy Garvin
Onboard NOAA Ship Rainier
June 1 – 8, 2005

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, AK
Date: June 5, 2005

Weather from the Bridge

Latitude: 56 deg 59 min N
Longitude: 135 deg 17 min W
Visibility:12 nautical miles
Wind Direction: 275 deg
Wind Speed: 10 kts
Sea Wave Height: 1-2 ft
Swell Wave Height: 0 ft
Sea Water Temperature: 54deg F
Sea Level Pressure: 1016 mb

Science and Technology Log 

Instead of running survey lines on a launch today, I was assigned to the plot and holograph rooms to learn what happens to the survey data when launches return to the RAINIER each evening.  Depending on the weather conditions, launches return to the ship each afternoon between 1630 (4:30 p.m.) and 1730 (5:30) p.m. Once they have been raised out of the water with the gravity falls davits, the survey techs plug the launch’s computer system into the main system on RAINIER.  At this time, the data is pushed (or downloaded) to the ship’s main network.

Two different software programs are used in the process; the launches use a program called ISIS to run the sonar, while the GPS mapping software onboard is Caris.  Therefore, the data collected on the launches must be converted into a form that can be read by Caris. During the conversion process, data corrections are made based on predicted tides, the sound velocity curve created by the CTD, filtering out the outer, less reliable sonar beams, and total propagated error (a statistical compilation of error based on the specific error inherent within each system).

Once the data has been converted, the survey techs go through each line individually and clean the line by removing random sonar reflections.  These reflections can be due to kelp beds, schools of fish, the boat’s motor, or internal timing of the sonar.  Once all of the lines on a sheet are complete, the sheet is sent to PHB (Pacific Hydro Branch) where the data is used to make nautical charts that are used by the fishing and cruise industries, as well as by any others who navigate these waters.

Personal Log 

The CO of the RAINIER took me out on a skiff for a couple of hours today to see some of the bays near Sitka. We saw a harbor seal, a sea otter, and lots of bald eagles; the mountains seem to rise right out of the water, and they are absolutely breathtaking with their snow-capped tips.

NOAA Teacher at Sea
Christy Garvin
Onboard NOAA Ship Rainier
June 1 – 8, 2005

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, AK
Date: June 4, 2005

Weather from the Bridge

Latitude: 56 deg 59 min N
Longitude: 135 deg 17 min W
Visibility: 5 nautical miles
Wind Direction: 300 deg
Wind Speed: 10 kts
Sea Wave Height: 0-1 ft
Swell Wave Height: 0 ft (we are in a protected bay)
Sea Water Temperature: 53deg F
Sea Level Pressure: 1009.8 mb

Science and Technology Log 

On the RAINIER, the crew works right through the weekend, so the workday began at 0800; again, four launches were deployed to run survey lines and take bottom samples.  I was assigned to launch RA-3, and we worked an area on survey sheet Y.

Launch RA-3 ran approximately 40 miles of hydrography using the Sea Bat 8101 Multibeam Echosounder.  The Sea Bat is a 240kHz echosounder that measures the relative water depths across a wide swath that is perpendicular to the launch’s track.  The system is comprised of 5 main parts: the sonar processor, the sonar head, the sonar processor to sonar head signal and control cable, a color monitor, and a computer mouse.  The transmit array, which is a projector section of the sonar head, transmits a pulse of sound energy that travels through the water and is reflected by the sea floor or any object in its path. The reflected signal is received by the hydrophone section of the sonar head, digitized, and then sent to the sonar processor for beamforming.  The processor then generates a video display of the ocean floor that can be viewed on the color monitor.  The Sea Bat can “see” approximately 300 meters, but it is more accurate in depths of 150 meters or less.

The physical process of running survey lines with the Sea Bat is nicknamed “mowing the grass;” this is because the launch actually follows the parallel lines drawn by the survey techs and the launch’s path resembles an individual mowing a lawn.  The survey lines are displayed on a computer screen so the survey tech can highlight a given line for the coxswain to follow. As the launch approaches the line, the survey tech logs the computer data for each line.  Lines vary in length from a few meters to several kilometers.

Personal log 

I learned to drive the launch today, and it was a lot of fun.  I was able to “mow the grass” for about an hour, and I also drove during a man overboard drill.

Previous question of the day:  What is refraction? 

Answer: Refraction is the bending of a sound wave.  In the case of sound traveling through water, different temperatures and pressures cause sound to travel at different speeds; this in turn causes the waves to bend.