After performing a very nice “butterfly” pattern during the MOOMZ cruise, we sent sg158 offshore to start cross-shelf transects. Shortly after that, we started getting loads of roll retries and even a few roll errors – this means the internal motors were trying to shift the batteries and execute a roll to turn the glider and the motors either did not respond enough or did not respond at all. We panicked a bit a called Fritz at UW. He gently chided us for not digging a little deeper into the log files, and then suggested some glider magic:
Create a pdoscmds.bat file with these 3 lines and let the glider execute it during next phone call:
This ran the glider through a series of tests on the roll mechanism. Things seemed ok, but the problem continued to worsen as we made more and more dives. Eventually, the glider was stuck rolled partially to the starboard side, meaning all dives now executed as a slow clockwise spiral on the way down and counterclockwise spiral on the way up with no real control of heading.
Now, this meant sg158 had to be recovered. It wasn’t in imminent danger, but it was way (30+ nautical miles) offshore. Once again, Gadiel Alarcon sprang into action (on a Saturday and Sunday no less), and late on Sunday August 23 sg158 was safely recovered and brought back to Iquique.
On Monday, Laura emailed with Ruben Moraga at UNAP and they got sg158 turned off and stowed away. Now we’ll need to get the gliders shipped back to the US to replace sg157′s batteries and figure out what went wrong with sg158.
We’ve been experimenting with some power saving strategies on sg157 this week. In the plot of energy consumption, you can see that the blue 10V battery is draining a lot faster than the red 24V battery. The 10V battery powers the onboard computer and the scientific sensors. The 24V battery mainly powers the buoyancy pump. So, our energy consumption for science is rapidly outpacing our energy consumption for flying.
How to fix that? Shut off the science sensors! So we tried that starting MondayJun 08 by uploading a one-line science file:
// Science for OSU sg157 and/or sg158 with PAR sensor
/depth time sample gcint
1000 600 0000 600
This file determines that from the surface to 1000 m the sampling interval is 600 seconds (10 minutes), none of the sensors are turned on (0000), and the guidance and control interval (time between steering) is also 600 seconds. This had an immediate affect:
Notice the major drop near dive 540. This is great, it extended our mission duration from end of August to end of October! Nevermind the fact we are no longer collecting data … and this had an added complication of suddenly erratic flying by the glider. With the glider checking in only every 10 minutes to steer and make flying decisions, sg157 would fly past 1000 m, go to deep and rocket up to the surface in what I’m assuming is an emergency manuever.
Anatoli did some experimentning, and now we are flying with shorter gcints and the CT sensor on, consuming only slightly more power than everything off, and having no more erratic dives.
At the beginning of April, we had some extended 20 kt bursts of northerly winds off the Oregon shelf,
(image from www.orcoos.org)
and the glider observations show the upwelling response in the coasatal ocean with deep, cool, salty, low oxygen water moving up onto the shelf.
In addition, to the deep water moving up onto the shelf, the fresh water in the surface layer moves off the shelf, and phytoplankton blooms can be seen in the near surface chlorophyll fluorescence measurements. Compare these sections with the clasic winter conditions below.
Two OSU Seagliders (sg157 and sg158) were deployed on Friday Mar 6, 2009 off the coast of Iquique, Chile. sg158 was recovered yesterday, but sg157 remains, collecting observations of temperature, salinity, density, currents, chlorophyl, backscatter, CDOM and dissolved oxygen. sg157 will continue to fly a cross-shelf section from about the 200 m isobath to 100 km offshore until July or August.
Currently, sg157 is headed offshore toward 71 W in deep water, making full dives to 1000 m. sg157 is completing dives too quickly, about 180 minutes vs. 330 minutes optimally, which I think is due to the max pitch at +/- 30 degrees. However, the overall flight seems well tuned; I’m getting good low pitch and roll bias numbers.
sg157 is having some altimeter issues, when it comes up onto the slope, getting false returns, and turning around too soon. I’ll continue to work on that the next time we come on shore.