Jessica Cobley: Recalibrating, August 6, 2019

NOAA Teacher at Sea

Jessica Cobley

Aboard NOAA Ship Oscar Dyson

July 19 – August 8, 2019


Mission: Midwater Trawl Acoustic Survey

Geographic Area of Cruise: Gulf of Alaska (Kodiak to Yakutat Bay)

Date: 8/6/2019

Weather Data from the Gulf of Alaska:  Lat: 58º 44.3 N  Long: 145º 23.51 W 

Air Temp:  15.9º C

Personal Log

Currently we are sailing back across the Gulf of Alaska to the boat’s home port, Kodiak. I think the last few days have gone by quickly with the change of daily routine as we start to get all the last minute things finished and gear packed away. 

Since my last post, the definite highlight was sailing up to see the Hubbard Glacier in Disenchantment Bay (near Yakutat). WOW. The glacier is so wide (~6miles) that we couldn’t see the entire face. In addition to watching the glacier calve, we also saw multiple seals sunbathing on icebergs as we sailed up to about a mile from the glacier. 

We spent a few hours with everyone enjoying the sunshine and perfect view of the mountains behind the glacier, which form the border between the U.S. and Canada. We also had a BBQ lunch! Here are a few photos from our afternoon.

Hubbard Glacier
Sailing through little icebergs. The glacier went further than we could see from the boat.
Group photo of the science crew
Group photo of the science crew! Photo by Danielle Power

Another surprise was showing up for dinner the other night to find King Crab on the menu. What a treat! Most people are now trying to get back on a normal sleeping schedule and so mealtimes are busier than usual.

king crab legs
Our Chief Steward, Judie, sure does spoil us!

Lastly, the engineering department was working on a welding project and invited me down to see how it works. On the first day of the trip I had asked if I could learn how to weld and this was my chance! They let me try it out on a scrap piece of metal after walking me through the safety precautions and letting me watch them demonstrate. It works by connecting a circuit of energy created by the generator/welding machine. When the end you hold (the melting rod) touches the surface that the other end of the conductor is connected to (the table) it completes the circuit.

Jessica welding
Wearing a protective jacket, gloves and helmet while welding are a must. The helmet automatically goes dark when sparks are made so your eyes aren’t damaged from the bright light. Photo by Evan Brooks.


Scientific Log

Before making it to Yakutat we fished a few more times and took our last otolith samples and fish measurements. Otoliths are the inner ear bones of fish and have rings on them just like a tree. The number and width of the rings help scientists calculate how old the fish is, as well as how well it grew each year based on the thickness of the rings. In the wet lab, we take samples and put them in little individual vials to be taken back to the Seattle lab for processing. Abigail did a great job teaching where to cut in order to find the otoliths, which can be tough since they are so small.

Jessica and pollock otoliths
Our last time taking otolith samples from pollock. Photo by Troy Buckley

Another important piece of the survey is calibrating all of the equipment they use. Calibration occurs at the start and end of each survey to make sure the acoustic equipment is working consistently throughout the survey. The main piece of equipment being calibrated is the echosounder, which sends out sound waves which reflect off of different densities of objects in the water. In order to test the different frequencies, a tungsten carbide and a copper metal ball are individually hung below the boat and centered underneath the transducer (the part that pings out the sound and then listens for the return sound). Scientists know what the readings should be when the sound/energy bounces off of the metal balls. Therefore, the known results are compared with the actual results collected and any deviation is accounted for in the data accumulated on the survey. 

Calibration
Downriggers are set up in three positions on board to center the ball underneath the boat. They can be adjusted remotely from inside the lab.

After calibration, we cleaned the entire wet lab where all of the fish have been processed on the trip. It is important to do a thorough cleaning because a new survey team comes on board once we leave, and any fish bits left behind will quickly begin to rot and smell terrible. Most of the scales, plastic bins, dissection tools, nets, and computers are packed up and sent back to Seattle.

Gear packed
All packed up and ready to go! The rain gear also gets scrubbed inside and out to combat any lingering fish smell.


Did You Know?

Remember when you were a kid counting the time between a lightning strike and thunder? Well, the ship does something similar to estimate the distance of objects from the ship. If it is foggy, the ship can blow its fog horn and count how many seconds it takes for the sound to be heard again (or come back to the boat). Let’s say they counted 10 seconds. Since sound travels at approximately 5 seconds per mile, they could estimate that the ship was 1 mile away from shore. We were using this method to estimate how close Oscar Dyson was from the glacier yesterday. While watching the glacier calve we counted how many seconds between seeing the ice fall and actually hearing it. We ended up being about 1 mile away. 

Cheers, Jess

Julia Harvey: Calibration in Sea-Otterless Sea Otter Bay, August 7, 2013

NOAA Teacher at Sea
Julia Harvey
Aboard NOAA Ship Oscar Dyson (NOAA Ship Tracker)
July 22 – August 10, 2013 

Mission:  Walleye Pollock Survey
Geographical Area of Cruise:  Gulf of Alaska
Date: 8/7/13 

Weather Data from the Bridge (as of 21:00 Alaska Time):
Wind Speed:  10.42 knots
Temperature:  13.6 C
Humidity:  83%
Barometric Pressure:  1012.4 mb

Current Weather: A high pressure system is building in the east and the swells will increase to 8 ft tonight.

Science and Technology Log:

Before I begin, I must thank Paul for educating me on the calibration process.  Because calibration occurred during the day shift, I was not awake for some of it.

The EK60 is a critical instrument for the pollock survey.  The calculations from the acoustic backscatter are what determines when and where the scientists will fish.  Also these measurements of backscatter are what are used, along with the estimates of size and species composition from the trawling, to estimate fish biomass in this survey.  If the instruments are not calibrated then the data collected would possibly be unreliable.

Calibration of the transducers is done twice during the summer survey.  It was done before leg one in June, which began out of Dutch Harbor, and again now near Yakutat as we end leg three and wrap up the 2013 survey.

As we entered Monti Bay last night, Paul observed lots of fish in the echosounder.  This could pose a problem during calibrations.  The backscatter from the fish would interfere with the returns from the spheres.  Fortunately fish tend to migrate lower in the water column during the day when calibrations were scheduled.

This morning the Oscar Dyson moved from Monti Bay, where we stopped last night, into Sea Otter Bay and anchored up.  The boat needs to be as still as possible for the calibrations to be successful.

Monti and Sea Otter Bays Map by GoogleEarth

Monti and Sea Otter Bays
Map by GoogleEarth

Site of calibration: Sea Otter Bay

Site of calibration: Sea Otter Bay

Calibration involves using small metal spheres made either of copper or tungsten carbide.

Chief Scientist Patrick Ressler with a tungsten carbide sphere

Chief Scientist Patrick Ressler with a tungsten carbide sphere

Copper sphere photo courtesy Richard Chewning (TAS)

Copper sphere
photo courtesy Richard Chewning (TAS)

The spheres are placed in the water under transducers.  The sphere is attached to the boat in three places so that the sphere can be adjusted for depth and location.  The sphere is moved throughout the beam area and pings are reflected.  This backscatter (return) is recorded.  The scientists know what the strength of the echo should be for this known metal.  If there is a significant difference, then data will need to be processed for this difference.

The 38 khz transducer is the important one for identifying pollock.  A tungsten carbide sphere was used for its calibration. Below shows the backscatter during calibration, an excellent backscatter plot.

Backscatter from calibration

Backscatter from calibration

The return for this sphere was expected to be -42.2 decibels at the temperature, salinity and depth of the calibration  The actual return was -42.6 decibels.  This was good news for the scientists.  This difference was deemed to be insignificant.

Personal Log:

Calibration took all of the day and we finally departed at 4:30 pm.  The views were breathtaking.  My camera doesn’t do it justice.  Paul and Darin got some truly magnificent shots.

Goodbye Yakutat Bay

Goodbye Yakutat Bay

As we left Yakutat Bay, I finally saw a handful of sea otters.  They were never close enough for a good shot.  They would also dive when we would get close.  As we were leaving, we were able to approach Hubbard Glacier, another breathtaking sight.  Despite the chill in the air, we stayed on top getting picture after picture.  I think hundreds of photos were snapped this evening.

The Oscar Dyson near Hubbard Glacier

The Oscar Dyson near Hubbard Glacier

Location of Hubbard Glacier.  Map from brentonwhite.com

Location of Hubbard Glacier. Map from brentonwhite.com

Many came out in the cool air to check out Hubbard Glacier

Many came out in the cool air to check out Hubbard Glacier

I even saw ice bergs floating by

I even saw ice bergs floating by

Lots of ice from the glacier as we neared

Lots of ice from the glacier as we neared

Nearby Hubbard Glacier with no snow or ice

Near Hubbard Glacier

And there it is: Hubbard Glacier

And there it is: Hubbard Glacier

Hubbard Glacier

Hubbard Glacier

Hubbard Glacier

Hubbard Glacier

Did You Know?

According to the National Park Service, Hubbard Glacier is the largest tidewater glacier in North America.  At the terminal face it is 600 feet tall.  This terminal face that we saw was about 450 years old.  Amazing!

Read More about Hubbard Glacier