Saturday, May 3, 2008

Recovery Photos

Shortly after the last blog entry, we had some surprizing news from RU15. On one of its descents, it looks like the buoyancy pump got stuck. RU15 was descending, and went below our normal working depth of 100 m.
Realizing it was approaching is maximum depth of 200 m, and it wasn't making any progress with moving its buoyancy pump, the robot decided to jetison its safety weight, and make an emergency ascent. When RU15 got the surface it phoned home and told us what happened. it would now remain on the surface and await recovery.

Scott McLean and crew had the Divecom III standing by for a pickup. The the recovery team was assembled, leaving early monday morning, April 28.

First sighting of RU15 since its deployment on March 7. What a great feeling to get that phone call over the Iridium sat phone that the glider is in sight.

RU15 off Halifax. 53 days and 2600 km after deployment in New Jersey.

Scott McLean hooks the glider tail with Marlon's glider catcher.

Once the glider is in the recovery cart, everyone pulls.

Crew and robot are all safe on board. Two thumbs up!

Our favorite call on the sat phone - "The bear is in the igloo!"

Thanks to the fantastic crew in Halifax.
You brought this first I-COOL mission to a successful completion.

Monday, April 28, 2008

A Weekend Storm

Satellite Sea Surface Temperature (colors) image shows the clouds (white) associated with the weekend storm.

Strong currents to the west blowing us off the Halifax line. New waypoint set for offshore, HL3, perpendicular to the currents and back to the line.

Currents are stronger than we can fly against. Just have to wait them out.

Temperature section shows the surface layer deeping with the storm.

Fresh water at surface looks to be mixed with the water below.

Friday, April 25, 2008

Flight Tests

We just completed a work week's worth of flight tests on RU15 while coming in along the Halifax line. Some watching closely will noticed that we slowed down a bit midweek, even though currents were slow. We were testing the buoyancy pump. Instead of pushing and pulling a full cup of water, we tried smaller changes in buoyancy to see how the energy savings would effect our flight characteristitics. Pulling in less water slows the glider and saves energy on the pump, but then it takes extra time to get somewhere so you burn energy just keeping the lights on. The tests will help us optimize the settings for long duration flight. We are now back up to full speed.

The deep basin off Halifax turned out to be an excellent test bed. Water over 100 m deep that is so close to shore. So we took advantage of the natural topography on the way in.

We are now half way between HL3 and HL2. We moved the HL2 waypoint a bit to the northeast so that it is in between the shipping lanes.
RU15 is now set to just bounce back and forth between the point between the shipping lanes and HL3. We'll keep this pattern going for several days.
We'll keep one eye on the battery and the other on the weather. Scott & Marlon have all the equipment for recovery and a boat ready when its needed.

Currents are small. We need to line up that strong current jet to the northeast with some of the features in the temperature and salinity sections below.

Temperature section inbound on the Halifax line. Three layers. We really like the deepwater test bed we found on the way in.

And Salinity. The surface is freshening.

Monday, April 21, 2008

Progress Along the Halifax Line

RU15 made fine progress along the Halifax Line over the weekend. We are now 95 km from HL2. The SST image again highlights the advantages of an approach from the southeast. We are in the warmer water, that appears to head towards shore along this line and on the upshelf side. On the downshelf side of the Halifax Line, colder water appears to be heading south, against the direction we would want to head.

Currents remain low, 5 to 20 cm/sec.
Following Temperature and Salinity Sections are along the short piece of the transect indicated by the green (start) and red (stop) dots. We are crossing over the bank, and will be crossing back down the shoreward side as the day goes on today.

Above temperature section starts on the offshore side of the Halifax Line near HL4 (green dot above) and heads in towards shore. Nearly 70 km has been sampled. Three clear layers. A warm surface layer (5C), cold middle layer (3C), and warmer bottom layer (6C). As usual, plenty of fine scale structure for the modelers to average out. The location of the bottom showing the bank is indicated by the black color filled area at the bottom of the plots.

Salinty is also three layers, surface (32.2), middle (32.6) and bottom (33.4).

Friday, April 18, 2008

Last Leg

RU15 hit the HL5 waypoint this morning and is now turned and heading towards Halifax inbound on the Halifax line. Currents are low, we are running about 10 cm/sec or less. About 140 km to HL2, so about a week.
Batteries still looking good, as far as you can tell. Time to settle into a scientific sampling section to go with the shipboard data currently being collected.
Here's once example of the 3-D view of the full dataset so far. We'll be presenting this to K-12 teachers at tomorrow at Liberty Science Center. They have an activity to build their own gliders out of legos and stuff. NJNetwork is going to film our undergraduates with the gliders on wednesday next week. They asked for copies of any video or stills taken from the deployment or recovery. Finally our students will be presenting their work on this flight to the public on the Ag School's Field Day next saturday, which is near the time we can start thinking about recovery. NOAA asked for a quick 100 word write up for their newsletter. We have some great I-COOL stories to share. Thanks again to our Canadian partners.

4.74 km to the Halifax Line

RU15 just surfaced 4.74 km away from HL5, the outermost shelf point on the Halifax line. We should be there sometime later this morning. At that point we'll make the turn in. Mostly clouds in the imagery this morning,
so we'll see how that develops. Currents have remained low, so its not as critical as it was in the Gulf Stream region.
Here is the nearly final section that started when we left the Warm Core Ring, crossed the slopewater and shelfbreak, and made our way east to the Halifax line. Almost there.

Temperature along the section. nearly the full water column on the shelf is cold, something our battery guru's will be watching. At the right end of the section, you can see the black shading for the bottom trace, indicating that the altimeter has now been turned back on (thanks Scott M!)

Once we hit HL5 and make the turn, we'll start a new section on the webpage and configure things for a standard cross-shelf line. There is a shipboard cruise going on right now, so we hope to contrinbute some scientific data to that project on the way in. A new area for us, but we benefit from a lot of local knowledge up in Halifax. Thanks again to all up there for sending their help to bring this thing in.

Tuesday, April 15, 2008

Eastward to the Halifax Line

This Satellite Sea Surface Temperature Image pretty much sums it all up. Last week RU15 followed the narrow band of warm water northward up to the deep side of the shelf break. Note that while it was in deep water, the track of RU15 has that serrated knife edge look to it characteristic of the presence of inertial waves. A look back at current vectors from John's time series plots shows the expected rotation of the velocity vector.
RU15 then successfully crossed the shelf break over the weekend, and went far enough onto the shelf to pull out of the currents that were heading southward, back across. Currents remained low Sunday and Monday, as we continued northeast. With good progress being made, we switched our target on the Halifax Line to HFX5, the outermost point that is still on the shelf. From HFX5 we'll turn to the northwest and follow the Halifax line in. Estimated time to Halifax is about 12 days.

Once we reach HFX5, we'll start up a new x-section plot on the webpage. That should happen sometime thursday or friday.

Back home in New Jersey, RU05 left Massachusetts on April 3. RU05 should be hitting the offshore side of the Tuckerton Endurance Line about the same time as Ru15 hits the Halifax line.

We also have two more glider deployments scheduled for Tuckerton. If all goes as planned, by the end of this week, you should be seeing RU15 inbound on Halifax Line, RU05 inbound on the Tuckerton line, and RUo7 & RU20 outbound from Tuckerton. All from the comfort of your web-browser.

Sunday, April 13, 2008

A Quiet night on the Scotian Shelf

RU15 was successfully retasked to fly to the northeast, heading for the relatively warm and clear waters identified yesterday.
Currents are low, and not terribly different from the forecast we found.
A test version put together over the weekend is above.
You need to load it and something like double click on it to get it to zoom in to the "curly" vector forecast currents. Based on where the glider is now, the forecast says currents are to the southeast and low. The glider is reporting low currents more to the south. This could end up being a very useful tool with comparisons in this general agreement. We'll work more on this forecast product visualization on monday. It also sounds like Marlon is finding some relevant Canadian forecasts we can start looking at.

We are back to full water column sampling. The above section starts when we left the Gulf Stream Ring and started crossing the slope water. Most recent data is on the right. Surface temperatures are running about 2C. We want to head northeast into the water with 4C surface temperatures. RU15 has been on quite a journey. In the Gulf Stream we were looking at the differences between 22C in the Stream, 18C in the ring, and now we care about 2C versus 4C.

Saturday, April 12, 2008

Crossing the Shelf Break - A Friday Night Course Change

Here is the track map with the recent current vectors plotted. The new waypoint to the northwest discussed in the previous posting is shown. The issue was the strong currents to the west last night. We wanted to head east towards the Halifax Line, but we had no choice. Dave IM'ed in about 10 pm and said the currents are kicking RU15's butt. The deep ocean was pushing us west. So on friday night we decided to abandon the flight to the east on the deep side of the shelf break, and instead make the jump north onto the shelf, into shallower water, and, hopefully, weaker currents.
Dave changed the waypoint from straight east to straight north, and we switched to a stay deep behavior to avoid the stronger surface currents, flying between a depth of 30 m and 100 m. By morning we had crossed most of the shelf and were getting into slower currents.

Here's the plot of current speed and direction during the crossing. Lots of strong currents to the west on 4/11 that caused the problem. But as soon as we crossed, currents turned to southeast and tried to push us back off the shelf. The good news - at least it had an easterly component.

Here is a zoom in on the track. Our attempt to fly east did nothing but cause the small loop in the track just offshore the shelf break. We gave up on that and jumped across. Now that we are on the shallow side of the shelfbreak, we are heading northeast, towards the Halifax line and the favorable currents identifed by Scott & Marlon in the previous post. We are back to full water column sampling.
We have a much more restful night ahead of us.

The Approach to Halifax

Scott McLean sent this image last night. Average currents on the Scotian Shelf for spring based on models and moorings. There is a nearshore jet that turns offshore at Halifax and heads straight south. Based on the mean currents, we don't want to approach from the south. An approach from the southeast would be better.
Marlon Lewis sent the Chlorophyll images above (April 7) and below (April 8). Both show high Chlorophyll (red) east of Halifax. The high Chlorophyll water turns offshore at Halifax, heading south, then southwest. Images look similar to the mean flow currents above. These images also say don't approach Halifax from the south. Try to stay in the water with low Chorlophyll (blue) that extends far north along longiotude 62 W.

Last image in the story is the SST from April 11. Only clear image of the area in the last few days. The warmer water on the shelf (blue, 4C) extends
to the north along latitude 62W. South or Halifax, the very cold water (pink, 2C) is extending far offshore.
All this indicates that an approach to Halifax from the south would run into a steady headwind for nearly the entire crossing. It is better to work our way eastward into the relatively warmer (4C), and Chlorophyll free water, and approach Halifax from the southeast. We just changed the waypoint of RU15 to fly to the northeast into the favorable currents so nicely identified by our friends in Canada. Thanks Marlon & Scott.

Friday, April 11, 2008

Halifax Section

From Loder, Shore, Hannag & Perie, 2000. Deep Sea Research.

Tuesday, April 8, 2008

What a difference a month makes

If we left April 8 we would have to travel 230 km further south to get to the Gulf Stream

Gulf Stream March 7, 2008

Gulf Stream April 7, 2008

Favorable currents & a lucky break

RU15 made good progress during the night.
Temperatures are staying low.

A lucky break in the clouds. The only clear area offshore is right over RU15.
A new Zoom region as we approach the shelf break. We are heading east towards the X and the southern end of that eddy.

Currents have increased and are towards the east.

As we approach the shelf break this week, we'll be changing the scales on several of our plots to make them easier to read. Temperature and current scales will be adjusted for the smaller range. The SST Zoom has been zoomed even more. We'll restart the temperature sections so we can see the smaller scale fronts of the shelf.

Monday, April 7, 2008

On to the Next Eddy

RU15 had a weekend of favorable currents that swept it clockwise around the western and northern side of the southern eddy. We exited on the northeast side. After leaving the southern eddy, we retasked RU15 to head to 42N, 63 W based on the last good satellite image. We were hoping to hit the bottom of the northern eddy. Within a few hours we had a clear spot in the clouds. The northern eddy was still there, and we where headed in the right direction.
Heading up to the northern eddy we are starting to encounter a bit of a headwind. The last two vectors are opposing us. Still under 20 cm/sec, so we'll make progress against it. We'll let it run overnight to see if this persists.

Saturday, April 5, 2008

The Route to the Shelf Break

RU15 has looped around the western side of that eddy, and is now heading to the east along its northern side. Satellite imagery from today and yesterday is cloudy, so we can fly based on the image from April 3.
Here is a zoom in on the April 3 Gulf Stream image. The centers of the southern eddy and the northern eddy are labeled. The proposed route is to continue westward along the top of the southern eddy, jumping out on the northeast corner. We then follow the cold water up to the northeast towards the northern eddy. We use the western side of the northern eddy for the boost up to the shelf break.