Author: admin (Page 6 of 36)

Over the course of this week, the glider team pumped out a number of new model visualization products to aid in piloting.  We are now looking at 5 model out puts in total including RTOFS, Copernicus, OSCAR, HYCOM and GLOSEA5.  The only problem is, none of the 5 models we are looking at agree with the currents produced by the glider.

While RU29 is reporting that the current is strong to the north, the following are todays forecasts from our five models:

Copernicus Feb 12

Copernicus is showing 29 should be feeling the effect of warm core eddy as we fly the west side where we should be feeling a current flowing south-soutwest.

GLOSEA5 Feb 12

The British GOSEA5 model shows that the current should almost be predominately west with a little bit of a southern component.

HyCOM Feb 12

HyCOM shows a current mostly due south with little bit of a western component

RTOFS Feb 12

RTOFS is showing the glider entering a strong jet flowing to the south west.

OSCAR Feb 8

and OSCAR shows that we are in the middle of an eddy where there should be a very weak southward current.

The glider however is seeing a very strong current to the north which resulted in making 27 km progress during the last 13 hr segment.

The problem with this area is that the current is very dynamic making it nearly impossible for a 24 hr forecast to capture what is truly happening.  One forecast that is accurate however is the wind maps which are lining up nearly perfectly with the surface drift 29 sees when she is calling in at surfacings.

The next surfacing will be around 6pm tonight. Since we have no idea where the glider will be at this call with the lack of a reliable road map, we will grab the glider when it calls in and depending on its position, we will give it one of two way points (35˚, 12˚ or 35˚ 30  13˚) as we try and fight our way through the unknown current that is pushing 29 to the north.

Force Wind Sea & Honor

Over the past week Challenger blew through the eddy previously discussed and depicted by the copernicus model below.  The european model nailed the forecast here and the currents predicted nearly matched the currents reported by the glider perfectly

Looking ahead, we have three options of routes to take to reach Cape Town.  In the map below, we have the Copernicus forecast overlayed on NASA’s Jet Propulsion Lab’s forecast, OSCAR’s magnitude forecasts which both show signs of the eddy solar system which lies between the glider and the shore.  Last night a new waypoint was set to our North East to try and steer the glider north of the large warm eddy to the South West.  If this maneuver can be pulled off, we will then push along either the orange route or the magenta route in the map below.

A third option is highlighted in the map below of the Copernicus salinity field provided by Antonio.  If we are unable to get to the northern side of the warm eddy and end up being pushed south, there is a route that approaches Cape Town from the south, however this path is much riskier as it puts us dangerously close to the retroflection which threatens to throw the glider out into the Indian Ocean.

Finally, in the image below we have outlined the 250 nautical mile radius from Cape Town.  This distance is important as it is the rough equivalent of how far a potential recovery ship could travel in a 24 hr period.

Force Wind Sea & Honor

As we predicted heading into the weekend, Challenger hit the ground (or eddy) running flying close to 40 km in a day as she began to ride the eddy to the south.

This eddy is a force to be reckoned with and so to try and make sure she doesn’t get swept to the center as we continue to make our way around, at the next surfacing  the way point will be moved to the south west.

Taking a step back, we can see the road that lies ahead.  The green line in the image above shows the path we aim to take over the coming weeks, taking 29 south through the eddies that are rolling around the South African Coast before flying north into Cape Town.

Finally if we zoom out a bit further we get a very impressive view of the Agulhas current along with the retroflection back into the Indian Ocean resulting in the eddy formation process that has been key to both our current approach and when Challenger was leaving South Africa back in January of 2013.

Over the next few days, 29 will continue to make her way around our current eddy and we will do our best to position her for a graceful exit into the next.

Force Wind Sea & Honor

Now less than a thousand kilometers from the shores of South Africa, Challenger is breaking speed records as she navigates the outer edges of the eddies rounding the Cape of Good Hope

This is one of the most energetic areas of the world’s ocean where eddies spill from the Indian into the Atlantic Ocean and we are really seeing their intensity as they propel 29 at speeds upwards of 35 km/day.

Currently Challenger has entered one of these eddies that will carry her around through the weekend.  In the image above we have the breakdown of the eastward velocity (red means flux to the east while blue is to the west).  According to the Copernicus model which the glider currents are matching at the moment, the souther edge of this eddy is pushing at about .6m/s or 50 km/day!  Through the weekend we will try and keep the glider to the outside as it will be hard to break free if we fall too far into the middle.

As for the status of the glider,  we are steering much better now after a deeper investigation was conducted this week.  A few weeks back when the glider suffered from an underwater reset, the steering parameters that have been tweaked throughout the mission were reset as well.  As time passed the steering was getting worse until this week it was discovered that in the recovery process after the reset, there was an error in the steering parameter by an order of magnitude.  After adjusting this error, the glider is once again steering pretty well as seen in the figure below

As the Rutgers team battled winter storm Jonas over the weekend, Challenger managed to fight her way through to some favorable currents to the east.  The two models we use for piloting showed two eddies spinning in opposite directions just ahead of the glider, but as 29 approached, the currents reported began to resemble the eddy shown by Copernicus. The following images are the forecast for Copernicus (top) and RTOFS (bottom).

Since we will resume following Copernicus, the waypoint was pushed further east to  34˚30S 9˚E to take advantage of the bottom portion of this counter clockwise spinning warm eddy.  With the boost from this string of eddies, the glider has returned to speeds of 20 km/day for the first time since the underwater reset and the steering issues started a few weeks ago.

As for the condition of the glider itself, power is back up to about 2.5 AH/day meaning we have about 125 days of power.  The increased power is a combination of repeat call in and the tuning we are doing for the gliders flight parameters.

Our big problem right now is steering. We are in a minimum of the horizontal component of the earths magnetic field, which is located just west of South Africa. This could be a contributing factor. But our bigger fear is biofouling. The steering issues came on suddenly. For the initial months of the mission, we had excellent steering, with less than 5 degrees rms error. Around December we made a jump to about 15 degrees rms error. Then last week we made an even more sudden jump to about 50 degrees rms error and our speed made good towards Cape Town plummeted to 10 km/day.  If this is biofouling, it usually effects the vertical speed, slowing us down, reducing the flow over the rudder, and we loose steering.  So the fix is to increase vertical speed, but we don’t want to loose our sweet spot on the pump. So we are starting with adjustments to pitch.

We have been flying descents at 26 degrees and ascents at 22 degrees pitch. The 22 degrees helps us squeeze out a little more horizontal distance on each ascent, but it means a slower ascent. So we switched the pitch back to our standard 26 degrees for the full yo. Over the weekend we flew a couple of segments at our standard pitch to establish a baseline of performance to compare to testing done throughout the week. Meanwhile we will set up for a new series of steering diagnostics to be sent back with the science data files every surfacing.

As it looks now, if we can maintain this speed as we steer through the eddies ahead, we are still look at about 70 more days making our approach towards Cape Town.

Force Wind Sea & Honor

Now less than 1200km from the shores of Cape Town, Challenger is continuing to push onwards towards recovery.

Over the past week, RTOFS has continued to be our go to forecast model as lately it has been nearly spot on when compared to the currents being reported by the glider.

Despite having seemingly favorable currents, our progress made good has plummeted recently due to the compass errors 29 has been having.

Over the past couple months we have seen the heading error trending upward, however within the past few weeks it has sky rocketed.  This we presume is due to the magnetic lows associated with the region.  Back in 2013 when Challenger was leaving Cape Town we had similar issues which led to difficulty steering as well.

In order to combat these issues, Dave is devising a plan to try different pump and pitch angles to see if the angle the glider is diving and climbing will have a positive effect on the compass.

As we head into the weekend, we are pushing the gliders way point to the east as a precautionary measure.  Currently the east coast of the US is getting hit with a massive snow storm which among other things has the potential to knock out power to our facilities cutting our connection to the glider.

Force Wind Sea & Honor

Since Monday, Challenger has been fighting her way through where we thought there would be a strong warm core eddy, however the currents have been predominantly due east with not as much southern component as the european model suggested.

The currents reported by the glider seem to follow  the model output from RTOFS more closely, showing that the path we took followed the flow between a cold core ring to the south and a warm core ring to the north:

Comparing the two models, it almost seems like relative to RTOFS, copernicus is shifted to the south.  The jet 29 took by being pushed due east looks like it could be the same jet we wanted to take to the south in the copernicus model output

Outside of piloting, on Thursday at around 4am eastern time, Challenger succumbed to an underwater reset.  This has happened a few times in the past, but what happened was that while in mid flight, the computer will reset causing the glider to come to the surface unaware of what program it had been previously running.

This resulted in the glider drifting at the surface for a while until someone was able to grab a hold of it and get it back on its way.

Finally today we had nice finding in which the direction of the glider velocity and the current velocity are in exact agreement at exactly 90 degrees.  In order to make 90˚, the waypoint had to be set at an angle of 103˚ which means the glider is pulling to the left at 13˚.  We also believe that this heading offset depends on the direction we are flying,
meaning it may have to do with the compass, and the idea that we are in an area where the horizontal component of the earths magnetic field is at a minimum.  This test is exactly east, and almost anything we fly over the next couple of months will be mostly east.

Using this, we will continue to monitor the offset in our steering through the weekend

Force Wind Sea & Honor

After we last heard from RU29 Friday morning, the glider gave us a scare by not calling in until we were well into Saturday.
In total the glider was silent for about 23 hours before it called in to Teledyne’s dock server. After discovering this, Dave was able to grab a hold of it and get it back under control.

Now that Challenger is back, a new way point as 34˚ 30’S, 6˚ 00 E was issued to try and get the glider flying at a good angle as we enter the next eddy.  Once the entrance is made, the way point will be shifted as we do our best to ride the strong currents that lie ahead instead of dissecting the eddy through the middle.  Once we make our way through this eddy, we will be just 3 more major eddies away from a recovery approach in South Africa

RU29 in now less than 1400 km from Cape Town  as the crow flies; assuming the crow follows the great circle route.
The purple line in the image above is the likely path Challenger will take as we navigate the remaining eddy field dipicted by the Copernicus currents.  This predicted path is roughly 150 km longer at ~1550km between 29s last position and our goal.

Diagnostics wise, power use is still holding steady at 2.3 AH/day which will allow for about 146 more days on the battery clock.  Current speed made good towards Cape Town is also running about 28 km/day which means if all continues to go well we can reach our goal in about 60 more days.  Finally Steering rms error is still about 15 degrees.

Force Wind Sea & Honor

Now 1500km from Cape Town and 1100 km from the closest point of South Africa’s EEZ, Challenger continues to push onwards toward her goal of crossing the South Atlantic from East to West.

Over the past few days Challenger has been pushed further to the north than we wanted, but was still left in a position where we can follow the path outlined last time by the purple line in the image above.  In the coming weeks, we will aim to surf the southern side of the two eddies as we work East-Northeast across the stream coming around the edge of South Africa.

In order to make the entry point for the leading eddy, we will change the way point to 35˚S, 5˚E

Power use is remarkably steady at 2.3 Amp Hours/day.  The recent peak at 2.8 AH/day was when we turned on the altimeter to get across the final group of seamounts.

If our battery power calculations are correct, at this use rate, we have 150 days of battery power left on board. 1500 km to go with 150 days of power on board means we need to beat 10 km/day made good to make it. So far throughout the mission we have only come near that minimum once at 11km while presently we are closer to 30 km/day

And this speed is something we need to try and keep steady for as long as possible:

Currently, our average heading error (red) is small – only a degree or so, however  the standard deviation of the heading error (blue) is trending upwards.  This heading error is a sign of biofouling and most likely the barnacles which have plagued the long duration glider missions over the years.
As the critters grow, the vertical speeds slow down, less water flow over the fin, resulting in more heading errors.

Hopefully we’ll be able to maintain Challenger’s speed as we work our way from eddy to eddy and get to South Africa as soon as we can

Force Wind Sea & Honor

Through the winter holiday, Challenger continued to make good progress while not only breaking speed records for the mission, but crossed back over to the Eastern hemisphere for the first time since early 2013.

As Challenger continued her approach to the Prime Meridian, we saw a nice correlation between the currents across the board as the depth average currents from the glider matched the eddy in both copernicus and RTOFS.

While making her way across the southern edge of the eddy, Challenger broke her mission speed record, breaking 37 km/day.

Then as 29 finally crossed the Prime Meridian, the glider began to feel the push of the eastern side of the warm core eddy.  In order to avoid the seamount to the east, we let the glider follow the flow of the eddy and rode it to the north.  The seamounts although labeled as only reaching to 750m from the surface while Challenger  is diving to 550m, the depths are not always accurate and so we like to keep a level of caution when flying by one.  The altimeter was also turned on as a secondary temporary precaution.

So now the challenge is the biofouling.  We are not flying as deep to help save the pump and reduce the power draw, but we see the slow deterioration in steering and vertical velocity. So we are still in a race. We have to get to Cape Town before the biofouling slows our progress to the point where we loose our steering.

Now just 1750 km from where she was deployed in Jan 2013, we are looking ahead at the stream of eddies we will navigate in the coming months as we get Challenger back to South Africa and complete the flights for the South Atlantic.

Force Wind Sea & Honor