Tools of the Trade:
The Oceanographic Tripod

Measurements of marine parameters are often made with instrumentation that is attached to a fixed platform. We generally call these platforms 'tripods' because this classic three legged design is the most stable and popular.
A bottom tripod serves as a framework on which to fix instrumentation in exact positions in the water column, as a protective frame against natural and human intervention. It is often the case that oceanographic studies are performed in heavily fished areas. The tripod frame is designed to sit on the ocean bottom and tolerate large storm generated currents and hits from nets and other gear.

USGS Large Bottom Tripod Design

Figure 1 below shows a tripod which is being used at the USGS Long Term Monitoring program off Boston, MA. It carries sensors and systems for sediment sampling, bottom photographs, recovery, and measurement of salinity, temperature, current, turbidity and pressure. Scientists analyzing the data get a better picture of how storms such as nor'easters affect sediments (and hence pollutants) on the ocean bottom. It is deployed at a depth of about 32 meters.


Tripod schematic
Figure 1 		Legend

1 - Recovery float
2 - Acoustic release
3 - Rope cannister
4 - Battery pack
5 - Current sensors
6 - Main controller, data logging system
7 - Underwater camera
8 - Compass

This tripod is constructed from 4" dia. stainless steel pipe with 300 lb lead weights on each foot. It is recovered by sending an acoustic command through the water to the release, which lets go of the recovery float, pulling a lifting line out of the rope cannister to the surface, where it is recovered by a ship.


Tripod being deployed
Figure 2
The tripod in Figure 1 is being deployed from the USCG White Heath. All fitted out, it weighs about a ton.


Photo of ocean bottom
Figure 3: A photograph of the sea floor taken by the tripod's underwater camera system. On the right, the compass shows the direction of the prevailing current. On the left, the bottom of one of the current sensors is visible. A starfish can be seen bottom right. The rocks have been scrubbed clean of sediment by a recent storm.


Recovered tripod
Figure 4
Newly recovered from the sea floor at the end of an experiment, this tripod shows one of the greatest challenges to oceanographic instrumentation engineers: biofouling.
Maintained by Marinna Martini
Comments to: mmartini@usgs.gov

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