Tag: sonar

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Kathy Virdin, July 21, 2004

NOAA Teacher at Sea
Kathy Virdin
Onboard NOAA Ship Rainier
July 20 – 28, 2004

Mission: Hydrographic Survey
Geographical Area: Eastern Aleutian Islands, Alaska
Date: July 21, 2004

Time: 6:00p.m.
Latitude: 55 degrees 49.65 N
Longitude: 157 degrees 56 W
Visibility: 11 nautical miles
Wind direction: 350 degrees NW
Wind speed: 7 kts
Sea wave height: 0-1 ft.
Swell wave height:2-3 ft.
Sea water temperature: 12.2 C.
Sea level pressure: 1013.0 mb.
Cloud cover: Partly cloudy

Science and Technology Log

Today I was able to go out on a launch (small boat) that did survey lines for eight hours. After the launch got underway, we lowered the transducer into the water where it will send out a spray of sound (approximately 131 pings) that will be measured on the launch’s computers. We also did a Reson line measurement which can accurately measure depths of 40 meters. We drove the launch in a line that was approximately 4-5 miles long, then turned and went back on the next line. Each line took about 40 minutes and we were able to cover 7 lines today. So in all, we were able to chart an area of 4-5 square miles. We stopped every four hours to put down a CDT which checks salinity, density and temperature. This information was immediately fed into the computers so that it can adjust the speed of sound through the waters by these factors. This launch also has a motion sensor that can measure the pitch and roll of the boat and that is factored into the speed the sound travels, which gives the calculated distance to the ocean floor.

NOAA has about 8 or 9 ships that do hydrography work which is extremely important to scientific research, as well as commerce. About 90-95% of all goods used in the U.S. are brought to us by ships! So it’s vital that they have accurate information to chart their path through our waters. The RAINIER is the only ship in the world that can do all the hydrographic survey work that it does. It’s an honor to work on a NOAA vessel and all members of the NOAA corps must have a degree in one of the sciences. The swath or path of the sonar beam that our launch is sending out covers about 200 meters. We’re seeing the data that tells us that the depths in this area are 100 meters. We have successfully measured our plot of the chart today with multi-beam swaths that intersect at the outskirts with one another. This is another measure taken to ensure accuracy.

Personal Log

I asked a lot of questions today while we were surveying, as the field operations officer with us had time to answer them. The work was mostly being done by the computers, so we were watching and checking them periodically. I learned that the launches are expensive boats because of all the high-tech equipment they carry (all of it necessary to get the job done). When we came back to the RAINIER, the sun came out and we went up on the deck to enjoy the view. I saw puffins flying over the water, and one of them flapped its wings across the water as it skimmed along the surface. This was a treat to watch the puffins as they entertained us with their antics. Tomorrow, I’m looking forward to following up on the data that was gathered from the two launches that went out today. It will be scrutinized and evaluated by the survey technicians and then stored in the folder for the day.

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Kathy Virdin, July 20, 2004

NOAA Teacher at Sea
Kathy Virdin
Onboard NOAA Ship Rainier
July 20 – 28, 2004

Mission: Hydrographic Survey
Geographical Area: Eastern Aleutian Islands, Alaska
Date: July 20, 2004

Time: 2:20 p.m.
Latitude: 55 degrees 39.4 N
Longitude: 158 degrees 00.3 W
Visibility: 10 nautical miles (nm)
Wind direction: Northwest
Wind speed: 7 kts
Sea wave height: 0-1 ft.
Swell wave height:2-3 ft.
Sea water temperature:13.3 degrees Celsius
Sea level pressure:1010.1mb.
Cloud cover:3/8 partly cloudy

Science and Technology Log

Today we reached the point where we would begin our surveys. I watched the survey technicians lower a Seabird (sound velocity profile unit) into the water, then raise it back up and hook it into a computer, where they could download the information. This will give them the salinity (salt content), temperature and pressure of the water. They lowered the Seabird 117 meters down into the water, before retrieval. At the same time, from the hull of the ship, a transducer sound wave emitter is sending sound waves to the bottom and measuring the time it takes for their return. From this information, they will calculate the distance to the floor of the ocean. They use this data from the Seabird to help them make corrections in the sound wave speeds from the transducer. The salinity, temperature and pressure will cause variations in the speed of sound, so they need to correct for this effect to gain an accurate depth measurement.

This information is being processed and viewed by cartographers (map designers) who will take what data the RAINIER gives them to update old maps or develop new maps and charts. These maps are used by fishermen, geologists or anyone who navigates through these Alaskan waters. We are headed for the Shumagin Islands where we will send out launches (smaller boats) to measure depths in places where the Rainier might not otherwise go. I found it interesting to note that environmentalists would also use this information, since they know where certain species of fish are likely to live, and they can decide how best to protect them if they are endangered. We will go back and forth three times in one plotted line to make sure our data is accurate and complete. When we send out a launch in more shallow water, they will use a different sonar device, called a Reson. It emits higher sound waves which will give a more accurate reading. For middle to deep depth measurement, they will use the Elac sonar and a vertical beam echo sounder which goes straight down that can be used for shoreline measurements. Because Alaska has such rough terrain, it’s important to get accurate measurements for those who use her waters.

Personal Log

I am amazed by how specific the data is that the survey technicians collect and how well everyone knows their job. This is truly a finely tuned, professional organization. Everyone has been so kind to answer my many questions even though I’m sure I’ve gotten in their way. I’ve spent a lot of time in the Plot room, where the data is logged into the computers and then interpreted by the technicians. Outside, it’s a beautiful, sunny day, which is the first pretty weather we’ve had. We saw a pod of whales, recognizable by the blow of water coming from their nostrils. I could see them really well through the high-powered binoculars that belong to the ship. I am working on a list of questions that I will use to interview different members of the crew, as well as the scientists so I can take this information back to my students, as they learn what the roles are on a NOAA vessel. Someday, I want my students to be the next generation of scientists that use the knowledge we are gaining today to frame the discoveries they will make in the future.

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Sena Norton, July 8, 2004

NOAA Teacher at Sea
Sena Norton
Onboard NOAA Ship Rainier
July 6 – 15, 2004

Mission: Hydrographic Survey
Geographical Area: Eastern Aleutian Islands, Alaska
Date: July 8, 2004

Location: Sonar Patch cruise, SE of Devils Bay on AK peninsula
Latitude: 55 46.163 N
Longitude: 158 03.557 W
Visibility: < 1 nm
Direction: 229 degrees
Wind Speed: 16 kt
Sea wave height: 1-2 ft
Swell wave height: 1.2 ft
Seawater temperature: 8.9 deg C
Sea level pressure: 1021.1 mb
Cloud Cover: n/a fog
Weather: Fair and foggy, 8.9 deg C dry / 9.4 deg C wet

Plan of Day: 1.5 days of sonar readings in patch with lines of 2.5 hours each. Launch #5 boat for survey north of ship around a possible rock pinnacle.

Science and Technology Log

Sonar Systems on board RAINIER: How they work.

What is Sonar?

In its most basic sonar are sound waves that are produced and then bounced back off of an object and recorded. Since the speed of sound is a known figure, the amount of time it takes for the sound wave to return to the transmitter/receiver gives a collectable image of that object. The deeper objects are the longer the sound wave takes to bounce back. Two types of sonar are single beam and multi-beam. Single beam is able to give high detail to an object but only shows a narrow swath, while multi-beam has a large footprint and can show a larger over all area. There are limits to the depth sonar can go because of the density of the water column. If the water is very dense the sound waves are slowed down and do not transmit the correct timing, therefore the image will be distorted. All images created must be analyzed after the density, temperature and salinity of the water column is taken into consideration.

Sonar is a very powerful sound wave and it can be dangerous, although it is at a frequency that humans or marine mammals cannot hear. If a diver were scanned they would be susceptible to a high-level concussive power. The emitter itself requires a large volume of power and if a human were to be near it during an emission it would do a great deal of damage. Think of the concussion from a bomb or firework, sonar is many, many more times as powerful.

RAINIER’s Sonar:

The ship is equipped with a deep sonar transmitter; it is attached to the hull and is used for scanning deep water where resolution is not a large issue. The boat “mows the lawn” in a patch of ocean. Each pass is numbered and the data collected. The lines are about 2 hours at 7-8 knots long. For more detailed work or a smaller area the ship will use one of its 6 launches that are also equipped with various sonar transmitters. These small boats will conduct and similar pattern of lines and collect the data right on board. The data is then transferred to the computers on board to go through technician cleaning and final analysis.

Sonar Types:
Single-beam – one beam sent and received.

Multi-beam – up to 240 beams per 180 degrees sent and received. As depth increases the foot print widens.

Analysis of data:

When the soundings are collected they are run through a Carris computer program where the technicians can manually scan each line. There are techs assigned to each “sheet” or area. Each line is cleaned, meaning outliers are removed or other “noise” is deleted. Once the data is clean a complete 3-D image of the patch can be looked at with all the data points represented. Once an entire area has been scanned objects become very clear, as if you were looking at them. From outlines of sunken ships from the side to large monolithic rocks protruding from the ocean floor, the detail and accuracy of the image is amazing. Once there is enough data the sounds can be turned into color-coded overlays that fit right on top of the fathom charts, so as to give a 3-D view of what those fathom readings represent. Red and orange or shallow and the colors move through yellow, green and finally blues, which are the deepest readings. Mountain ridges, lava floes, old wrecks, valleys and monoliths all come to life on the chart.

Personal Log

Steve Foye gave me a quick training with another new member of the crew on the job of Lookout on the flying bridge last night. He reviewed the 32-point compass and the difference between saying North relative to the ship verses trying to figure out the “real” compass coordinate. He explained you could use directions (NW or SE) or give the coordinates (90 or 270). Dead ahead would be 000, north relative to the ship or 360, all are correct for locating something directly off the bow of the ship.

Question of the Day:

When is the ship required to sound foghorn and place lookouts on the Bow/Flying Bridge?

When the visibility gets below 1 nm the ship is required to blow the foghorn or ring a bell every 2 minutes. A lookout is placed on the flying bridge during hours of darkness or low visibility. They move to the bow when the foghorn is turned on so they do not damage their ears.

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Leyf Peirce, July 6, 2004

NOAA Teacher at Sea
Leyf Peirce
Onboard NOAA Ship Rainier
July 6 – 15, 2004

Mission: Hydrographic Survey
Geographical Area: Eastern Aleutian Islands, Alaska
Date: July 6, 2004

Time: 20:00
Latitude: N 59°03.205
Longitude: W 150°41.139
Visibility: 10 + mi
Wind direction: 280
Wind speed: 11 knots
Sea wave height: 0 – 1 foot
Swell wave height: 3 – 4 feet
Sea water temperature: 12.2 °C
Sea level pressure: 1016.0 mb
Cloud cover: 4/8

Science and Technology Log

We left Seward today and are headed toward the Shumagin Islands to conduct hydrographic surveys to map the ocean floor and the coastline. The overall goal of this research is to update existing nautical charts. Most of the charts that are currently used have not been updated since the early 1930’s. After talking with ENS Brent Pounds, ENS Nicole Manning and P.S. Shyla Allen, I learned more about the tools and techniques used to map the ocean floor. Steve Foyd also provided me with an excellent pamphlet titled “Nautical Chart Programming”. From these sources, I learned the following information about data acquisition and analysis. The RAINIER will first be positioned using the Differential Global Positioning System (DGPS) near the desired area to be mapped. Then, the RAINIER launches up to 6 research vessels, each equipped with two main measuring devices. One device, the ELAC C-Beam 1180, is basically a side scanner that can scan a swath of the bottom of the ocean up to 200 meters using 180 individual sound beams. Any depth change will appear to be different shades on the sonogram. The heights of different points can then be calculated from this sonogram. In conjunction to the ELAC C-Beam 1180, the launch boats use an echo sounder mounted to the ship’s hull. While this can retrieve more accurate data, data with only a 0.1 m margin of error, it can also only scan an area up to 5 meters. However, using these two systems combined produces the most accurate data. The RAINIER also installs tide gauges that produce accurate data that can be added to the resulting nautical charts. Researchers aboard the RAINIER take this data, “clean it”, and eventually send it to the mainland to be used to create the new updated charts.

Personal Log

This day has been full of excitement as we are finally underway! The scenery is absolutely beautiful here, and the wild life is truly fascinating. The snow covered mountains dip into the water with an awesome power as sea otters and puffins play in that same water below. We have also seen several porpoises and one crewmember claimed he saw a whale. I am overcome with awe at how this ecosystem is filled with so much wonder and unknown as the mountain goats and moose mirror the whales and sea lions only to be separated by where the land and water meet. Life aboard ship is similarly full of excitement. It is like a finely tuned machine how well everyone works together to make this boat maneuver. As much as I am enjoying the sight seeing, I can’t wait for the research to begin. I am excited to have my engineering background meet my teacher profession!

Question for the Day:

It is summer here, and the tilt of the Earth causes the “sun to never go down”. One could even read a book in the middle of the night with no flashlight! As I was thinking about navigational techniques and the history of navigation, I couldn’t help but reflect on the importance of using the stars for guidance at night. The question for the day is: What did sailors use, before all of the GPS technology we have now, to navigate at night in these upper latitudes when it never got dark enough to see the stars at night?