One of the interesting innovations on the RV Hugh R Sharp is the incorporation of a “CTD Handling System” from Caley Ocean Systems. The video above was taken from the wet lab of a CTD Rosette being deployed and recovered using this system. If you search around on YouTube, you can find some interesting videos of crews deploying and recovering the CTD Rosette system. What you typically find is that you have one crane operator and then two or three crew members on deck with poles and/or ropes to try and guide the CTD back onto the deck. With the ship rocking and rolling out to sea, this can be a tad dangerous, especially when much of this work is done close to the waterline with waves splashing on deck.
The marine technician on the Sharp is up on the bridge level and looks down through windows at the wet lab area and beside the ship. This allows them to control the deployment and the recovery of the CTD from a much safer location. The Caley CTD Handling System has motion compensation built in to cancel out the roll and pitch of the ship and is designed to mostly eliminate the swaying of the CTD system. This makes for a much smoother and safer CTD deployment and recovery, which can occur quite often on many research vessels. The following pictures show the control station up on the bridge and an exterior view of the Caley CTD Handling System onboard the Sharp.
Next time I’m out on the Sharp, I’ll try to get a view of the system in action from outside the wet lab.
Is the system perfect? No, they still have some kinks to work out and with Caley located over in the UK, turn-around time can be pretty slow at times. The vessel operators are taking some lumps and trying to iron the kinks out of a system that can help make it a little safer to do routine underway CTD casts. Their efforts should be applauded.
September 1, 2010 / dw / Comments Off on CTD and Dissolved Oxygen Measurement via Winkler Titration
Last fall I was on the RV Hugh R Sharp for a short research cruise out in the Delaware Bay. We were sharing the Sharp with chief scientist Dr. George Luther, who was doing a mooring deployment that contained a dissolved oxygen sensor (among several other sensors). As part of the calibration check to make sure the readings were correct while we were on station, Dr. Luther did several CTD casts to take some water samples at various depths. I snagged the trusty video camera and got him to explain what he was doing and why.
To verify the accuracy of modern electronic oxygen sensors, oceanographers still verify the dissolved oxygen concentration using what’s called the Winkler test for dissolved oxygen. Dr. Luther showed the process of fixing oxygen into a MnOOH solid, which is then measured by the Winkler titration. This allows scientists to compare the oxygen readings they’re getting now with historical records of oxygen levels going back to the late 1800’s (an important thing to do when you’re trying to determine long-term trends by comparing historical records against more recent observations). It also allows them to verify the readings that they’re getting from modern electronic oxygen sensors.
I’ll sneak down to Dr. Luther’s lab soon and video the second part of the process, where they add the additional chemicals to the mix and determine the actual concentration of dissolved oxygen. Thanks again to Dr. Luther for taking time to explain the process.
Some students and I went on a road trip to Rutgers University in New Jersey and then ended up heading up the coast to East Falmouth, Massachusetts to meet with the fine folks at Teledyne Webb Research. During a tour of the facilities, we were introduced to the APEX floats, whose data (through the ARGO program) the students were accessing for various projects in the ORB lab. James Truman, an engineer at Webb, graciously agreed to do a quick 101 overview of the APEX on camera.
Profiling floats like the APEX are able to sink or float by varying their internal volume. A standard equation for Buoyant Force is:
F(buoyant) = –pVg
where p=density of the fluid, V=volume of the object (in this case the float) and g=standard gravity (~9.81 N/kg). By adjusting the internal volume of the float by pumping fluids in and out of the interior, we are able to make the device either more or less buoyant. There’s a really neat cut-away animation on the UCSD Argo site that shows the guts of the units quite well.
Float technology has evolved rather quickly, with the original floats only serving as a mechanism for tracking deep ocean circulation – also called Lagrangian Drifters or ALACE (Autonomous Lagrangian Circulation Explorer) floats. They would pop up to the surface and transmit back their positions and the temperature at depth. Using the drifters last known position and its new position gave scientists an idea of how fast and in what direction the deep ocean currents were moving. Later these drifters were equipped with CTD sensors (Conductivity-Temperature-Depth) and they took sensor readings all the way up the water column and transmitted a “profile” reading back to the mother ship. These were called PALACE or “Profiling ALACE” floats (see WHOI’s site on ALACE, PALACE and SOLO Floats).
NOAA has a site called ARGO KMZ Files that makes it really easy to get started tracking ARGO floats and their data. You just need to install Google Earth first – which can be downloaded at: http://earth.google.com/. Below is a screen shot of the ARGO floats in the Atlantic.
Thanks again to James Truman and the awesome people at Webb Research for taking us under their wing and spending a lot of time showing us the ropes. It was an excellent experience that the students are still talking about.
How many times have you been standing on a dock or a bridge or even out on a kayak or large research vessel and found yourself wondering what the temperature, sound and salinity profile was for the water beneath you? Well, you need wonder no more!
Here’s the last of the videos from the BEST Workshop last week. I talked with Chris from YSI about their new product the portable “Castaway CTD”. Just a tad larger than your standard handheld GPS, the Castaway CTD is a battery operated unit that allows you to do on-the-spot CTD casts at depths up to 100 meters. Chris did a quick rundown of the unit and its operations and then we stepped inside to see what software they are supplying to pull the data off the units, manipulate it and export it for use. Again the venue was quite noisy, so my apologies for the poor sound quality.
Specs for the unit are available on the YSI site, just click on the “Specifications” tab. The unit runs on two AA batteries, which they claim will run the unit for over 40 hours. Communications with the unit are via an internal BlueTooth radio and the unit ships with a tiny USB BlueTooth dongle for you to use in your computer. The recorder comes with 15MB of storage, which they claim will store over 750 casts. It contains a built-in GPS so that you can get a geographic fix on your location within 10 meters and it will record the following: