Tag: aleutian islands

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.

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

Mission: Hydrographic Survey
Geographical Area: Aleutian Islands, AK
Date: June 2, 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 (we are in a protected bay)
Sea Water Temperature: 54deg F
Sea Level Pressure: 1016 mb

Science and Technology Log 

Each evening aboard the RAINIER a POD, or plan of the day, is posted to inform all hands of the work scheduled for the following day. The POD for today, Thursday, June 2, showed that work would officially begin at 0800.  Two launches were to be deployed in order to run survey lines; I was assigned to launch RA4 working near Sitka and off Baranof Island. Running survey lines is one of the most important tasks accomplished by the RAINIER.  Since the ship’s scientific mission is hydrography, or charting of the ocean floor, the running of these lines is a major part of accomplishing that task.

Before the launches can actually run survey lines, there is a lot of preparation that takes place behind the scenes in the plotting room.  Here, each area to be surveyed is subdivided into smaller plots and placed on survey sheets to make large areas more manageable.  Then, a survey technician pulls existing nautical charts of the area and uses previously obtained depth information to determine where and how far apart to space the survey lines. In order to ensure 100% coverage of the ocean floor to the 8-meter mark, survey techs multiply the depth in fathoms (a fathom is 6 ft) by 5 to calculate the meters of line spacing.  For example, if a launch is working in an area that is 7 fathoms deep, then the amount of space between the survey lines in that area would be 35 meters apart. The closest any lines are drawn is 25 meters apart.

Once the distance between lines has been established, the survey tech draws the lines on a map of the area.  Lines are drawn parallel near the shoreline since close lines are necessary to achieve 100% coverage. Further from the shore, lines can be drawn in any direction, but they are usually drawn parallel to each other for ease in running the lines.  These maps are taken out on the launches and entered into a specialized computer program that helps the launch find and follow the survey lines that have been drawn.

Personal Log 

One of my favorite activities today was having the chance to drive the launch during a man overboard drill.  I’m sure the life preserver in the water (our man overboard) breathed a huge sigh of relief that it wasn’t run over by the crazy coxswain (driver) at the helm.

Question of the day: What is a CTD? 

Previous question of the day: What is hydrography and why is it necessary? Answer: Hydrography is the charting of the ocean floor. It is necessary because many ships use the information on the charts to ensure safe passage through narrow or shallow channels. Many of the old charts contain data that is very old or that was obtained by unreliable methods.  It is important that charts are updated so that ships are able to pass through these areas safely.