Slocum Glider Recovery Procedure (Remote Pilot)¶

This guide describes the standard actions carried out by a remote (on-shore) pilot before, during, and after recovery of a Slocum glider. For the corresponding field-team actions, see Field Recovery Procedure.

Source

Paraphrased from NorGliders / University of Bergen (UiB) field procedure notes (SL12 — User Notes — G3 Recovery Remote Pilot).

Consider the environment, vessel traffic, local operating conditions, and the glider's battery health — is it safe to keep the glider on the surface for an extended period? Adjust timing to the situation. We typically set the glider to drift 60 minutes before the field team is due on site, but if arrival time is uncertain, set it to drift earlier — the glider should already be drifting by the time the field team arrives.

1. Pre-Recovery Coordination¶

Discuss with the field team beforehand:

Estimated time the field team arrives on site, and the likelihood of the schedule shifting.
Estimated time of recovery (e.g. after a CTD cast).
Method of communication, and how often the field team will receive glider position updates.
Glider configuration: call-in interval, strobe function, etc.

2. Catch the Glider on the Surface¶

Several hours before the planned recovery, catch the glider on the surface and shorten the surfacing interval by editing yo10.ma/yo14.ma and/or surfac01.ma/surfac21.ma.

3. Set the Glider to Drift¶

About 60 minutes before the field team is due on site:

Turn off the XML script in SFMC.
Run the commands below to set the glider to drift.

Iridium and GPS share an antenna

You cannot use both at the same time. Periodically hang up the Iridium phone (callback 10) to let a fresh GPS fix through, and check the fix's age in the surface dialog. If the GPS device has been taken out of service, put it back with use gps.

Commands — Set Glider to Drift¶

Command	Description
`^c`	Stop the current mission and return to `gliderDOS>` (repeat if several missions are sequenced).
`put u_max_time_in_gliderdos 14400`	Drift this many seconds before `lastgasp.mi` runs automatically — 2 hr = 7200, 4 hr = 14400, 12 hr = 43200, 24 hr = 86400.
`put c_de_oil_vol 420`	Set the oil pump to maximum buoyancy.
`strobe on`	Turn the strobe on (unless in broad daylight).
`callback 1`	Hang up and call back in 1 minute — use to force a fresh GPS fix while staying connected.
`callback 15`	Hang up and call back in 15 minutes (or 5/10/30, depending on the situation) once finished communicating.

Other Useful Commands¶

Command	Description
`where`	Display the surface dialog — GPS fix, time, and other sensor values. Also a good way to just confirm the glider is connected.
`report ++ m_gps_lat`	If the field team has a FreeWave receiver and is nearby, turn on reporting of a sensor so they pick up a signal as soon as they're in range.
`put u_iridium_max_time_til_callback 1800`	Change the default Iridium callback interval (default 600 s). Keep it at least 5 minutes less than `u_max_time_in_gliderdos`, and be sure you're OK not hearing from the glider for that long.
`use`	List sensor devices and check whether any are out of service.
`use gps` / `use all`	Return GPS, or all devices, to service.
`report clearall`	Stop reporting a sensor.

Disabling devices to save battery

If the glider is low on battery, disable non-essential devices — but only after setting max buoyancy and confirming with get m_de_oil_vol:

use - hd_pump attitude_rev ocean_pressure vacuum pitch_motor digifin altimeter science_super leakdetect

The glider will ask you to confirm with y for each device — type quickly, and double-check the command before sending it. Never disable Iridium or GPS.

Dropping the weight

Only do this if there is genuine concern about the glider's buoyancy — once dropped, the glider cannot overcome positive buoyancy and can no longer dive or continue a mission.

put c_weight_drop 1
put c_weight_drop 0
put m_weight_drop 0

The glider will report that the burn wire has activated; give it a minute to burn, then zero the sensors as above. You will likely need exit reset to clear the messages — do this before disabling other devices, or you'll need to do it twice.

Depending on how far away the field team is, either stay connected or run a drifting script from the SFMC glider terminal (e.g. Callback5.xml, Callback10.xml) to have the glider hang up and call back the primary number every 5 or 10 minutes.

4. Position Monitoring¶

If the field team doesn't have direct SFMC access, provide regular position updates from the GPS Location value in the surface dialog, noting how many seconds old the fix is. Refresh it roughly every 300 seconds, or more often if the glider is drifting significantly.

5. FreeWave Communications¶

If the field team is running a FreeWave receiver, or the glider is very close to the ship, Iridium call-ins may stop — the glider prioritizes FreeWave when it finds a receiver, or the ship may be blocking the satellite signal. This is expected behaviour.

6. Deploy the Nose Recovery System¶

Deploy the nose recovery line when the field team is about 10 minutes from the glider, or as soon as they have visual contact. Inform them that release isn't instantaneous — the line is wound on a spool and takes several minutes to uncoil — and to let you know if it doesn't release.

Command	Description
`put c_recovery_on 1`	Activate the nose recovery line.

7. During Recovery¶

Expect reduced communication while the field team focuses on retrieval — continue providing position updates and be ready to help troubleshoot (see below) if needed.

8. After Recovery¶

Once the field team confirms the glider is safely aboard the research vessel (not the workboat), have them position it with a clear view of the sky, then run the shutdown sequence:

Command	Description
`put c_air_pump 0`	Deflate the air bladder.
`put c_de_oil_vol -420`	Retract the ballast pump for safe storage.
`get m_de_oil_vol`	Confirm the pump reaches −420 after a few minutes.
`exit`	Shut down the glider — confirm with `y` once you're sure (via the field team) that it's safe to do so.

9. Post-Recovery¶

Note the UTC hour and minute you shut the glider down, and tell the field team they have exactly 30 minutes from that time to remove the green plug and install the red plug.

Troubleshooting: Nose Recovery Line Not Deploying¶

A nose line has never failed to deploy so far, but two things could cause it: the burn wire hasn't burnt through, or the recovery spool is fouled or caught on something in the nose cavity.

Action	Description
Retry	Send `put c_recovery_on 1` again.
Boat hook assist	Have the vessel come alongside and tap the yellow nose cone with an extended boat hook, at several angles.
Shallow dive test	Command a dive to ~10 m via `yo14.ma` — if the wire has burnt, the buoyant nose may lift off on its own.
Deploy workboat	If none of the above works, consider a workboat recovery.