SIO OBS Tour

August 9th, 2010

As part of my summer internship I was able to take a tour of the IGPP OBS lab. Like the construction of land seismometers at PASSCAL, the OBS lab technicians start out with an intact sensor ball, a Trillium 240. Within the sensor ball lies a spring system with X, Y and Z components that sense perturbations. Ironically this massive ball does not store any of the data it collects nor does it contain its’ own power source. These are located in the lager and battery bottles. The lager stores both the memory (through a simple flash drive) and the clock on memory boards as well as serves as a battery source. Active source seismometers can suffice from the power stored in the lagers (short deployment) where as passive experiments require additional battery bottles. The clock used in the SIO OBSs, called a c-scan, has the precision of 50 parts per billion, meaning it loses only ~1.5 seconds/year.The technicians use a Gimbel system for quality control to level the sensor ball (precautionary measure as the sensor ball contains an additional level). The Gimbel system also serves as a skeleton for the sensor ball to hang from a frame. An SIO OBS frame houses several features. The yellow container holds four glass balls used for flotation in device retrieval. The lager, battery bottle and a pressure sensor sit below the glass balls. The frame is connected on the bottom to an anchor the weighs the system to the ocean floor. When an OBS is ready for retrieval, an acoustics system responds to an individualized sequence of pins at a particular frequency and burns off a link that holds the system together. Malfunctions in the acoustic and flotation system can cause device loss (a particular problem in the PLUME deployment).

This yellow lager can weigh
up to 90 pounds when full!

A technician working on a Trillium 240

An SIO OBS frame (stored at IGPP)...must turn your head to the right