Mission Plan
Mission Plan

Education
Education

Thunder Bay
Thunder Bay

Shipwreck Vignettes
Shipwreck Vignettes

Sonar and AUV Technology
Sonar and AUV Technology

launching an AUV
Launching an AUV

Recovering an AUV
Recovering an AUV

Explorers
Explorers

Information

 

 

Here is the AUV just after it was spotted on the surface. In this photo, it is relatively easy to see, but since the waves are higher that the antennas and fins, it was often hidden by the waves.

Here is the AUV just after it was spotted on the surface. In this photo, it is relatively easy to see, but since the waves are higher that the antennas and fins, it was often hidden by the waves. Click image for larger view and image credit.

Recovering an AUV

Charles Loeffler
Senior Engineering Scientist
Applied Research Laboratories
University of Texas, Austin

camera icon A short video of the AUV recovering. (Quicktime, 660 Kb)

Recovering an AUV can be as exciting and anxious as launching.  Before the AUV surfaces, you do not know exactly where it will appear because underwater navigation is very difficult and the AUV is usually slightly lost.  It is hard navigate underwater because there is no underwater GPS, there are no “wheels” touching the lake bottom to measure the distance traveled, and sometimes compasses on vehicles, which are made out of metal and have electric motors, are not very accurate.  (Actually, this is similar to walking at night in very dark woods by just counting your steps while using a cheap compass.)  Any errors in distance or heading will cause errors in the perceived location (for the AUV or hiker).  On an AUV, this error is usually tens of meters and sometimes can be hundreds of meters, but if a compass is off 5 or 10 degrees, the error can be kilometers.

A small boat is often used to attach a line or cable to the AUV. In this sea-test, they used a RHIB, which is a hard-bottomed boat with inflated rubber sides. Once the AUV is secure, they towed it over to the support ship to hook to the crane and lift out of the water.

A small boat is often used to attach a line or cable to the AUV. In this sea-test, they used a RHIB, which is a hard-bottomed boat with inflated rubber sides. Click image for larger view and image credit.

Sometimes the AUV is quickly lifted to avoid being hit by a rising wave.

Sometimes the AUV is quickly lifted to avoid being hit by a rising wave. Click image for larger view and image credit.

When the AUV is expected to surface, the crew on the surface ship will go to the approximate location and begin scanning the area.  Spotting the AUV on the surface can be difficult.  Even though it is bright yellow, it floats very low in the water and can be obstructed by the waves.  When the vehicle surfaces, it flashes its strobe and tries to contact the support ship via its WiFi and underwater acoustic modem.  If it connects, its GPS location is sent to the surface ship.  When the AUV is spotted or a connection is established, the ship usually maneuvers close to the AUV and either waits for the AUV to continue its mission by submerging again or to begin recovery operations. If the AUV is not spotted or if it does not make a communications connection with the ship, then it calls the ship’s computers via a satellite phone, and the crew will sail to the AUV’s reported location.

The AUV recovery procedures are in reverse order of the launch.  First the AUV must be grabbed.  Sometimes a long pole can be used to reach the AUV.  Other times the AUV is farther away, and a few crew members take a smaller boat out to the AUV where they are able to reach over the side to grab it.  After securing the AUV, they will tow the AUV back to the ship. Once there, a shackle on a cable from the crane is attached to the lifting strap on the top of the AUV, then the tension is slowly increased to check the shackle and the balance of the AUV. If everything is ok, it is lifted high above the water and finally lowered into its cradle on the deck of the ship.  After rinsing the AUV with fresh water, the power and data cables are connected to charge the batteries and upload sonar data to the mapping computers.  

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