Coordinated Robotics

The Lagrangian Float: A Profile

SOI/ Logan Mock-Bunting
Mar. 30 2015

One of the autonomous underwater vehicles being used on the Coordinated Robotics cruise is a Lagrangian Float. Named after the famous French mathematician Lagrange, Lagrangian Floats do not move on their own, but instead float in the water. Scientists can program the 60 lbs. float to submerge, drift, or stay exactly two meters off of the bottom. It is a light-weight, simple platform that consists of a big aluminum tube with batteries, electronics, and a computer inside.

William Snyder and Professor Chris Roman troubleshoot power issues before launching the Lagrangian Float for the first time.
William Snyder and Professor Chris Roman troubleshoot power issues before launching the Lagrangian Float for the first time.SOI/ Logan Mock-Bunting


Spaghetti lines
There is also a camera system strapped to the side of the float. As the float moves it can take photographs of the ocean bottom at timed intervals. This provides scientists with a long, linear visual strip of the sea floor, which they refer to as a “spaghetti” drift track. This squiggly line shows the float’s route with corresponding photos. The trick with getting good seafloor images is to have a constant distance, so that the focus and scale is always consistent.

Georgiy Pleskach and William Snyder work on wiring the Lagrangian Float in Falkor’s Wet Lab on the journey to Scott Reef.
Georgiy Pleskach and William Snyder work on wiring the Lagrangian Float in Falkor’s Wet Lab on the journey to Scott Reef.SOI/ Logan Mock-Bunting
Lagrangian Float is lowered from Falkor’s aft deck into the water. Photo credit:
Lagrangian Float is lowered from Falkor’s aft deck into the water. Photo credit:SOI/ Logan Mock-Bunting

Drifting towards greatness
The float is not limited to just photography: it is a general platform as well. “We have done water column work looking for phytoplankton and oxygen layers, and are treating the ‘float’ like a pick-up truck that we can strap things to,” explains researcher Chris Roman. “On this trip we’ve attached a camera, but we can take it off and strap other sensors to it, like a shallow-water drifting tool. To my knowledge, there are not many other floats like this in the world. We have a novel instrument and now we are finding uses for it,” Roman explains.

Different tools to drive down costs
Every AUV on board will achieve something different, and by coordinating these complementary aspects, the team can see a bigger picture of the marine environment. While the float is at the whim of the currents, the science team and crew can strategically stack the deck by putting the float in a smart spot. The science team tries to place the Lagrangian Float so it will drift over a previously mapped grid. They can take the ‘spaghetti track’ of the float and compare it to other more organized AUV tracks.

This strategy is a major part of thinking about the total aggregate survey of an area over time. It helps to reduce monitoring costs associated with AUV’s and cross-register the track data. Researchers can survey locations with the more precise AUV first, then follow up with vehicles like the Lagrangian Float to determine if further assessment is necessary. One of the goals of this project is to find different ways of doing work without extreme costs. On this cruise, the science team is trying to get different tools to work together.
The Lagrangian Float waits to be loaded onto Falkor after a successful mission.
The Lagrangian Float waits to be loaded onto Falkor after a successful mission.SOI/ Logan Mock-Bunting

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