Track line for glider sg158 lauched at the beginning of August
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:
menu hw/pitch/read
menu hw/roll/read
menu hw/roll/rolls
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.
Last 1000 m dive from sg158 stuck rolled to starboard
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.
sg157 stopped communicating with the basestation sometime late last Friday (06/26/09). sg157 disappeared for 4 days, and then finally called in Tuesday evening. Anatoli and Justin handled it like pros, and figured out that the glider had happily continued to dive and receive GPS fixes, during it’s seclusion. This means there’s nothing wrong with the antenna and that the antenna is getting far enough out of the water. It also means that there’s nothing mechanically wrong with the glider.
The problem appears to be isolated to the Iridium satellite phone communications.
sg157 has been calling in more consistently since then, but misses a scheduled call in every now and then …
Out plan is to continue to fly sg157 onshore. If we get another big disappearance, then we’ll have to figure out an emergency recovery. If things continue to go OK, then we’ll send Laura out at the beginning of August to put sg158 in before the MOOMZ cruise, and we’ll send Justin out at the end of August to recover sg157.
Energy usage plot for sg157 since the beginning of the deployment.
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:
10V battery energy usage by sensor, major consumers are optics and TT8 (computer)
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.
In this post we share a short video documenting how we launched the gliders in Chile.
Before we get to the video, though, I’d like to extol one of the [major] benefits of using gliders as a tool in Oceanography: they are easy to launch and recover from small vessels. “Traditional” oceanography takes place on large research ships (well over 100 feet long), which is problematic in terms of the costs involved (very expensive) and their limited availability. Launching or retrieving a glider from a small boat is simple and inexpensive, and if we need to get out on the water for an unplanned emergency rescue, small boats are relatively easy to come by. Case in point: this was our small-yet-capable Chilean launch vessel, which belongs to the Universidad de Arturo Prat (UNAP):
R/V Antares
We launched two gliders and recovered one from this nimble little vessel. While the rest of the research team was stranded on land after our larger research vessel blew an engine, the OSU Glider Research Group was still able to get out there and save the day with gliders (fist bump!).
Okay, on with the video:
Thanks to Laura for sharing her photos and video from the trip!
The change to the science file didn’t result in any substantial energy savings. See the blue line on the plot below
Ideally the blue and red curves, should parallel one another. We’ll have to try something more severe in terms of sampling the lower portion of the water column to save energy.
Dive 236 uploaded new science file to decrease energy consumption and match buoyancy energy rate.
// Science for OSU sg157 and/or sg158 with PAR sensor
/depth time sample gcint
50 4 1111 60
150 4 1111 120
250 16 1110 180
600 52 1110 300
1000 104 1100 360
The projected recovery date is currently end of July, this may buy us some more time.
Yeah, Anatoli! He got the dive speeds down from 180 minutes to 260 minutes (30 cm/s to 10 cm/s), and the results is extended mission duration and better vertical resolution in the profile data! Check out the latest profiles and you’ll see a much clearer picture of the small scale subsurface maxima in chl or DO:
Here’s the cmdfile that did the trick:
$D_TGT,990
$T_DIVE,470
$T_MISSION,390
$HEAD_ERRBAND,30
$ROLL_ADJ_DBAND,3
$ROLL_ADJ_GAIN,0.03
$ALTIM_PING_DEPTH,400
$ALTIM_PING_DELTA,20
$ALTIM_SENSITIVITY,4
$MAX_BUOY,100
$SM_CC,300
$C_VBD,2630
$C_PITCH,2500
$C_ROLL_DIVE,2500
$C_ROLL_CLIMB,2400
$GO
A new ratio for D_TGT and T_DIVE (not 3 anymore) and limiting the buoyancy range from 200 down to 100 with MAX_BUOY. This slows the dive thru buoyancy without altering the range.
sg157 continues to head offshore almost to 71 W now. For the last ten dives (85-95), sg157 has been collecting chl, backscatter and cdom observations over the entire 1000 m. I have now turned off the optics after 600 m depth. This deep water should have minimal signals (i.e. zeros), and will provide a means for Amanda to estimate drift in the optical measurements.
The oxygen minimum is still clear, but the layer seems to be getting thinner (250 m vs. 300 m). My plan is to continue offshore until sg157 exits the OMZ or 71.5 W.
sg157 continues to make full 1000 m dives on its way offshore. The top of the OMZ has been deepening in the offshore direction, and now the top is at about 100 m. Measurements from the upcast (red) are more reliable due to the large time constant associated with the DO sensor.
I’m tuning the roll a little bit and dialing back the vbd:
cmdfile:
$C_VBD,2720
$C_ROLL_DIVE,2500
$C_ROLL_CLIMB,2400
$GO
And, per Amanda’s request I’m going to turn on the optics for the full depth for a few dives.
// Science for OSU sg130 initial deployment
//depth time sample gcint
50 4 111 60
100 4 111 120
250 8 111 180
600 48 111 300
1000 96 111 300
See sg157 full observations
http://gliderfs.coas.oregonstate.edu/sgliderweb/seagliders/sg157/current/procdat/index.php?