Tag: acoustic doppler

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Bhavna Rawal: Net Tow, Dive, Buoy Maintenance and Data Collection, August 8, 2012

NOAA Teacher at sea
Bhavna Rawal
On Board the R/V Walton Smith
Aug 6 – 10, 2012

Mission: Bimonthly Regional Survey, South Florida
Geographic area: Gulf of Mexico
Date: August 8, 2012

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Weather Data from the Bridge:
Station: 21.5
Time: 1.43 GMT
Longitude: 21 23 933
Latitude: 24 29 057
Wind direction: East of South east
Wind speed: 18 knots
Sea wave height: 2-3 ft
Clouds: partial

Science and Technology Log:

Yesterday, I learned about the CTD and the vast ocean life. Today I learned about a new testing called net tow, and how it is necessary to do, and how it is done.

What is Net Tow? The scientist team in the ship uses a net to collect sargassum (a type of sea weed) which is towed alongside the ship at the surface of the predetermined station.

A net to collect sargassum (a type of sea weed)
A net to collect sargassum (a type of sea weed)

How did we perform the task? We dropped the net which is made of nylon mess, 335 microns which collects zooplanktons in the ocean. We left this net in the ocean for 30 minutes to float on the surface of the ocean and collects samples. During this time the ship drives in large circles. After 30 minutes, we (the science team) took the net out of the ocean. We separated sargassum species, sea weeds and other animals from the net. We washed them with water, then classified and measured the volume of it by water displacement. Once we measure the volume, we threw them back into the ocean.

Dropped the net which collects zooplanktons in the ocean
Dropped the net which collects zooplanktons in the ocean
Types of sargassum
Types of sargassum
Measured the volume of it by water displacement
Measured the volume of it by water displacement
Threw them back into the ocean
Threw them back into the ocean
Record data

Types of Sargassum and Plankton:  There are two types of sargassum; ones that float, and the other ones that attach themselves to the bottom of the ocean. There are two types of floating sargassum and many types attached to bottom of the ocean.

Also there are two types of plankton; Zooplankton and phytoplankton. As you all know phytoplankton are single celled organisms, or plants that make their own food (photosynthesis). They are the main pillar of the food chain. It can be collected in a coastal area where there is shallow and cloudy water along the coastal side. The phytoplankton net is small compared to the zooplankton and is about 64 microns (small mess).

Zooplanktons are more complex than phytoplankton, one level higher in their food chain. They are larva, fish, crabs etc. they eat the phytoplankton. The net that is made to catch zooplankton, is about 335 microns. Today, we used the net to collect zooplankton.

Why Net Tow is necessary: Net tow provides information about habitats because tons of animals live in the sargassum. It is a free floating ecosystem. Scientists are interested in the abundance of sargassum and the different kinds of animals, such as larva, fishes, crabs, etc. Many scientists are interested in the zooplankton community structures too.

Dive, Buoy and other data collection equipments: Two science team members prepared for diving; which means that they wore scuba masks, oxygen tanks and other equipment. They took a little boat out from the ship and went to the buoy station. They took the whole buoyancy and other data collection instruments with them. The two instruments were the Acoustic Doppler (ADCP) and the micro cat which was attached to the buoy. The micro cat measures salinity and temperature on profile of currents, and the ADCP measures currents of the ocean. Both instruments collect many data over the period. The reason for bringing them back, is to recover data in a Miami lab and the maintenance of the buoy.

The micro cat measures salinity and temperature on profile of currents
The micro cat measures salinity and temperature on profile of currents
Acoustic Doppler (ADCP) measures currents of the ocean
Acoustic Doppler (ADCP) measures currents of the ocean

Personal Log:

My first day on the ship was very exciting and nerve-racking at the same time. I had to take medicine to prevent me from being seasick. This medicine made me drowsy, which helped me to go to sleep throughout the night. The small bunk bed and the noise from the moving ship did not matter to me. I woke up in the morning, and got ready with my favorite ‘I love science’ t-shirt on. I took breakfast and immediately went to meet with my science team to help them out for the CTD and net tow stations. Today, I felt  like a pro compared to yesterday. It was a bit confusing during the first day, but it was very easy today.

I started helping lowering the CTD in the ocean. Now I know when to use the lines for the CTD, water sampling for different kinds of testing, how to net tow and do the sargassum classification. I even know how to record the data.

When we have a station call from the bridge, then we work as a team and perform our daily CTD, water testing or net tow. But during the free time, we play card games and talk. Today was fun and definitely action packed. Two science team members dove into the ocean and brought the buoy back. I also saw a fire drill.

Nelson (the chief scientist) took me to see TGF or called the flow through station which is attached inside the bottom of the ship. This instrument measures temperature, salinity, chlorophyll, CDOM etc. Nelson explained the importance of this machine. I was very surprised by the precise measurements of this machine. Several hours later, I went to the captain’s chamber, also called the bridge. I learned how to steer the boat, and I was very excited and more than happy to sit on the captain’s chair and steer.

Excited to sit on the captain’s chair and steer the R/V Walton Smith

We have also seen groups of dolphins chasing our ship and making a show for us. We also saw flying fishes. In the evening, around 8 o’clock after dinner, I saw the beautiful colorful sunset from the ship. I took many videos and pictures and I can’t wait to process it and see my pictures.

Saw groups of dolphins ahead of ship

Around 10 o’clock in the night, it was net tow time again. We caught about 65 moon jelly fishes in the net and measured their volumes. Nelson also deployed a drifter in the ocean.

See moon jelly fish in my hand

Today was very fun and a great learning opportunity for me, and don’t forget the dolphins, they really made my day too!

Question of the Day:
How do you measure volume of solid (sea grass)?

New Word:
Sargassum

Something to Think About:
Why scientists use different instruments such as CTD as well as TFG to measuretemperature, salinity, chlorophyll, CDOM etc?

Challenge Yourself:
Why abundance of sargassum, types of animals and data collection is important in ocean?

Did you Know?
The two instruments were the Acoustic Doppler (ADCP) and the micro cat which was attached to the buoy. The micro cat measures salinity and temperature on profile of currents, which means it measures at surface of the ocean, middle of the ocean and bottom layer of the ocean too.

Animals Seen Today:
Five groups of dolphins
Seven flying fishes
Sixty five big moon jelly fishes
Two big crabs

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Diana Griffiths, June 24, 2006

NOAA Teacher at Sea
Diana Griffiths
Onboard UNOLS Ship Roger Revelle
June 22 – June 30, 2006

Mission: Hawaiian Ocean Timeseries (WHOTS)
Geographical Area: Hawaiian Pacific
Date: June 24, 2006

Weather Data from Bridge 
Visibility:  10 miles to less than 25 miles
Wind direction:  065°
Wind speed: 06 knots
Sea wave height: small
Swell wave height:  4-6 feet
Sea level pressure: 1014.5 millibars
Cloud cover:  3, type:  stratocumulus and cumulus

Buoy Technician, Sean Whelan, contacting the Acoustic Releases on WHOTS-2.
Buoy Technician, Sean Whelan, contacting the Acoustic Releases on WHOTS-2.

Science and Technology Log 

Today was very busy because it was the day that WHOTS-2 mooring, which has been sitting out in the ocean for almost a year, was recovered.  At around 6:30 a.m., Sean Whelan, the buoy technician, tried to contact the Acoustic Release.  (The Acoustic Release is the device that attaches the mooring to the anchor. When it receives the appropriate signal, it disengages from the anchor, freeing the mooring for recovery.  There are actually two releases on WHOTS2.) He does this by sending a sound wave at 12 KHz down through the ocean via a transmitter, and when the release “hears” the signal, it returns a frequency at 11 KHz. The attempt failed, so the ship moved closer to the anchor site and the test was repeated.  This time it was successful.  Based on the amount of time it takes the acoustic signal to return, the transmitter calculates a “slant range” which is the distance from the ship to the anchor. Because the ship is not directly over the anchor, this slant range creates the hypotenuse of a right triangle. Another side of the triangle is the depth of the ocean directly below the ship.  Once these two distances are known, the horizontal position of the ship from the anchor can easily be calculated using the Pythagorean theorem.

Recovery of WHOTS-2 buoy aboard the R/V REVELLE.
Recovery of WHOTS-2 buoy aboard the R/V REVELLE.

After breakfast, the buoy recovery began. A small boat was lowered from the ship and driven over to the buoy, as the ship was steamed right near the buoy. A signal was sent down to activate the Acoustic Releases. Ropes were attached from the buoy through a pulley across the A-frame, located on the stern of the ship, to a large winch.  With Jeff Lord leading the maneuvering of the 3750-pound buoy, it was disengaged from the mooring and placed safely on deck.  This was a bit of a tense moment, but Jeff did a wonderful job of remaining calm and directing each person involved to maneuver their equipment to effectively place the buoy. Once the buoy was recovered and moved to the side of the deck, each instrument on the mooring was recovered.  The first to appear was a VMCM, (Vector Measuring Current Meter) located just 10 meters below the buoy.

Jeff Lord, engineering technician, directing the recovery of a Vector Measuring Current Meter (VMCM).
Jeff Lord, engineering technician, directing the recovery of a Vector Measuring Current Meter (VMCM).

Then two microCATs were pulled up, located 15 and 25 meters below the buoy, followed by a second VMCM. This was followed by a series of eleven microCATs located five or ten meters apart, an RDI ADCP (Acoustic Doppler Current Profiler), and two more microCATs.  As each instrument was recovered, the time it was removed from the water was recorded and its serial number was checked against the mooring deployment log.  Each instrument was photographed, cleaned off and sent to Jeff Snyder, an electronic technician, for data upload. Each of these instruments has been collecting and storing data at the rate of approximately a reading per minute for a year (this value varies depending on the instrument) and this data now needs to be collected. Jeff placed the instruments in a saltwater bath to simulate the ocean environment and connected each instrument to a computer by way of a USB serial adaptor port. The data from each instrument took approximately three hours to upload. Tomorrow, these instruments will be returned to the ocean alongside a CTD in order to compare their current data collection with that of a calibrated instrument.

Once all of the instruments were recovered, over 4000 feet of wire, nylon rope, and polypropylene rope were drawn up using a winch and a capstan. Polypropylene rope is used near the end of the mooring because it floats to the surface.  The last portion of the mooring recovered was the floatation.  This consisted of eighty glass balls chained together and individually encased in plastic. The glass balls, filled with air, float the end of the mooring to the surface when the Acoustic Releases disengage from the anchor.  It takes them about 40 minutes to reach the surface. Recovering the glass balls was tricky because they are heavy and entangled in one another. Once on deck they were separated and placed in large metal bins. After dinner, a power washer was used to clean the buoy (it is a favorite resting place for seagulls and barnacles) and the cages encasing some of the instruments.  The deck was cleaned and organized to prepare for tomorrow.

Recovery of mooring floatation on WHOTS-2, consisting of 80 glass balls encased in plastic.
Recovery of mooring floatation on WHOTS-2, consisting of 80 glass balls encased in plastic.

Personal Log 

The theme that keeps going through my mind during this trip and today especially, is how much of a cooperative effort this research requires. It begins with the coordination between Dr. Weller and Dr. Lukas to simultaneously collect atmospheric data using the buoy and subsurface data with the mooring instruments. In addition, Dr. Frank Bradley, an Honorary Fellow at the CSIRO Land and Water in Australia, is on the cruise working to create a manual set of data points for relative humidity using an Assman psychrometer to further check the relative humidity data produced on the buoy. Within the science teams, coordination has to occur at all stages, from the collection of data to its analysis. This was very evident in physical form today with numerous people on deck throughout the day working to retrieve the mooring, fix machinery as it broke down (the winch stopped twice), and clean the instruments.  In the labs, others were working to upload data and configure computer programs to coordinate all of the data.  In addition to all of this is the quiet presence of the ship’s crew who are going about their duties to be sure that the ship is running smoothly.  Several of the crew did take a break today just after the instruments were collected in order to put out fishing lines!  They caught numerous tuna and beautiful Mahi Mahi that the cook deliciously prepared for dinner.