Rita Salisbury: Underwater Navigation, April 24, 2013

NOAA Teacher at Sea
Rita Salisbury
Aboard NOAA Ship Oscar Elton Sette
April 14–29, 2013

Mission: Hawaii Bottomfish Survey
Geographical Area of Cruise: Hawaiian Islands
Date:
April 24, 2013

Weather Data from the Bridge:

  • Humidity 71%
  • Wind SpeedS 8 mph
  • Barometer30.07 in (1016.2 mb)
  • Dewpoint65°F (18°C)
  • Visibility

Science and Technology Log

I wish everyone could see how hard the scientists work on solving problems as they crop up. Their collaboration skills are top-notch. Everyone has something to contribute and their ideas are listened to respectfully. Solutions belong to everyone on the team. It also seems to me that there is a lot of “cross-training” going on, too. Everyone has a specialty, but others are capable of taking over or filling in for that person. That goes for the deck crew as well as the scientists. Every event has a planning meeting in which roles are defined and strategy determined.

Every large event gets a planning meeting to go over the details.

Every large event gets a planning meeting to go over the details.

One of the thrusters on the AUV had to be replaced and the new one is considerably heavier than the original one. That means that the whole buoyancy of the AUV is impacted. It needs to be a little light so its natural course is to float to the surface. The new thruster changed the weight of the AUV so the scientists had to calculate and design a remedy for the issue. They decided to add high density foam to the AUV to increase the buoyancy. They used high density foam because regular foam would compress at the depths to which the AUV submerges. This AUV is designed to go down 2000 meters, but others go as deep as 6000 meters.

High-density foam used for bouyancy

High-density foam used for bouyancy

In order to confirm that their calculations for the amount and placement of the new foam were correct, the AUV was put over the side of the ship and tests were run. It was always attached to the crane, as a precaution, but the cables were slack and the AUV had the opportunity to be tested. Once the tests were run, the scientists reviewed the results and decided to send the AUV out on a mission.

I asked Jeremy Taylor, one of the scientists, about how the AUV navigates underwater to the various coordinates pre-programmed into it. If it starts at Point 0, 0, how does it get to Point X,Y? Global Positioning Satellites are not any help since GPS doesn’t reach underwater.  Jeremy explained to me that the AUV actually navigates by altitude, not depth. It has 4 beams positioned on the frame in various locations that combine their information to tell the AUV how far above the sea bed it is. This kicks in when the AUV is about 35 meters above the bottom. From that information, the AUV keeps a certain distance above the sea floor and can then navigate over formations on the floor that stand between the AUV and its’ destination, the Point X,Y location. Using the altitude navigation system means the AUV’s navigation is fairly simple and the person who programs it doesn’t have to worry about going around or over obstacles.

Personal Log
As one of the scientists, Erica Fruh, explained the reasoning behind the high-density foam being used for buoyancy, it made me think of a video on the Galapagos Islands that I have shared with my students. In the video, an ROV is deployed in the depths off the coast of one of the islands in the Galapagos chain. Someone put a Styrofoam head (the type used to hold wigs) in a basket on the outside of the ROV. After the dive, which went to considerable depths, the head was retrieved and measured. The weight of the water had compressed the head to about 1/4 of its original size. It was a very graphic demonstration of the compression that occurs in the depths of the sea.

Did You Know?
The pressure at 3000 feet deep in the ocean is 100 times more that of air at sea level. Check out this link for a visual of wig heads and styrofoam cups: http://oceanexplorer.noaa.gov/explorations/04etta/logs/aug27/aug27.html

Maria Madrigal: Understanding the Sampling Methods: April 4, 2012

NOAA Teacher at Sea

Maria Madrigal

NOAA Ship Oscar Elton Sette

April 2-18, 2012

Mission: Comparison of Fishery Independent Sampling Methods

Geographical area of cruise: Tutuila, American Samoa

Science & Technology Log: April 4, 2012

The goal of the study is to get a better picture of the coral reef fish assemblage using three different sampling methods. Two NOAA research vessels based in Honolulu, Hawaii (Oscar Elton Sette and Hi’ialakai) are working concurrently to assess coral reef fish assemblages around the island of Tutuila in American Samoa.

Three observational methods will be used to assess these reef fish assemblages; stationary point count divers (SPC), baited remote underwater video stations (BRUVS) and an autonomous underwater vehicle (AUV).

In the shallower areas being sampled (0 – 30 meters), all three survey methods will be used. In the areas ranging from 30-100 meters, only the BRUVS and AUV systems will be used as the divers can not reach these depths. This study will allow for a comparison among all three methods in the shallow-water depth range. The use of the BRUVS and AUV in the 30-100 m depths will also allow comparisons to be made between the shallow and deeper portions of the reef ecosystem to see if the patterns apparent in the shallow areas are similar to or different than those found in deeper waters.

SE12-02 Tutuila Comparison of Fishery Independent Sampling Methods for Coral Reef Fish

SE12-02 Tutuila Comparison of Fishery Independent Sampling Methods for Coral Reef Fish

The Hi’ialakai will be the base for the SPC (Stationary Point Count) divers.  Teams of two divers will work side-by-side sampling across a 30-meter transect. One diver is centered at the 7.5 meter mark and the other diver is centered at the 22.5 meter mark. Each diver samples a cylinder with a radius of 7.5 meters. Each diver spends the first five minutes noting the fish species present within their cylinder. After noting what fish species are present, the diver keeps a tally of how many representatives of each species are within their cylinder. Divers must work systematically to record additional data including total fish length and habitat type.  For a more detailed description of the SPC method, you may read the procedure as provided by PIFSC.

The Oscar Elton Sette will be the base for the BRUVS (Baited Remote Underwater Video Stations) and the AUV(Autonomous Underwater Vehicle) operations.

BRUVS are deployed from small boats at predetermined locations previously sampled by the SPC divers. They are placed on the seafloor and are equipped with two cameras that allow for accurate measurement of the fish that come into view. The BRUVS are deployed at each site for 20-minutes without bait and again for 60-minutes either with or without bait. The video can be instantly reviewed to ensure successful recording at each site. Captured video is reviewed and analyzed at a later date. Final video processing and data analysis will take place once the scientists return to the lab.

The AUV, named Lucille, is designed to hover 2-4 meters above the seafloor. It is programmed to navigate a predetermined survey track before it is deployed. It is equipped with a pair of forward-looking stereo-video cameras, two still-image cameras, a CTD (Conductivity-Temperature-Depth) sensor and a SONAR (Sound Navigation and Ranging) unit. It can dive down to 1,500 meters and can go on missions that last up to eight hours. It is programmed to come back to the ocean’s surface at the end of its mission.  The video and still photographs are later reviewed and analyzed. All the data collected by the AUV allows scientists to get a better picture of the ocean floor, what lives there and how many organisms are living within that community.

Comparison of Survey Methods

Comparison of Survey Methods