Glass-Ball Broadband OBS
These instruments are equipped with a Nanometrics Trillium Compact broadband seismometer and used for year-long monitoring of teleseismic and regional earthquakes.
Design and Specifications
Item | Specifications |
|---|---|
| Physical Attributes | Three 17" Nautilus glass ball pressure housings holding: (i) data-logger, storage device, controllers; (ii) acoustic-release board, WHOI recovery board, and lithium batteries; (iii) lithium batteries. One 17" Benthos ball for floatation. A 14" I.D. Al sphere holds seismometer and leveling system. Leveling is via a gravity-driven or motor-driven, 2-axis gimbal system that can be locked in place by motor-driven disk brakes mounted on each gimbal axis in order to record ground motion with high fidelity. A WHOI-designed controller is capable of locking/unlocking the seismometer masses, centering the masses, and activating/de-activating the disk brakes. The controller also carries a compass, temperature, and tilt sensor. The controller is capable of automatically monitoring seismometer tilt and intiating a leveling procedure if necessary. Air-weight (less 175 lb. anchor but with one-year battery pack) is 530 lbs. Water-weight on bottom (less sensor) is 65 lb. Buoyancy (less anchor) is 66 lbs. Descent rate: ~43 m/min. Ascent rate: ~ 43 m/min. |
| Data Logger | Three 17" Nautilus glass ball pressure housings holding: (i) data-logger, storage device, controllers; (ii) acoustic-release board, WHOI recovery board, and lithium batteries; (iii) lithium batteries. One 17" Benthos ball for floatation. A 14" I.D. Al sphere holds seismometer and leveling system. Leveling is via a gravity-driven, 2-axis gimbal system that can be locked in place by motor-driven disk brakes mounted on each gimbal axis in order to record ground motion with high fidelity. A WHOI-designed controller is capable of locking/unlocking the seismometer masses, centering the masses, and activating/de-activating the disk brakes. The controller also carries a compass, temperature, and tilt sensor. The controller is capable of automatically monitoring seismometer tilt and intiating a leveling procedure if necessary. Air-weight (less 175 lb. anchor but with one-year battery pack) is 530 lbs. Water-weight on bottom (less sensor) is 65 lb. Buoyancy (less anchor) is 66 lbs. Descent rate: ~43 m/min. Ascent rate: ~ 43 m/min. |
| Clock | Seascan low-power, digitally-temperature-compensated (DTCXO), clock with drift rate, before end-point correction, of <5 ms/day. |
| Sensors | Nanometrics Trillium Compact broadband seismometer with a velocity response that is flat from 120 seconds to 100 Hz. When deployed, the seismometer package is mechanically decoupled from motion of the OBS frame. Differential Pressure Gauge (DPG) long-period pressure sensor. |
| Recording Duration | Lithium battery pack for ~15 months recording at 100 Hz. Keep-alive battery for clock. |
| Operation | Operated in closed-ball mode i.e. programming of acquisition parameters, offloading of data, clock setting, etc., all done through penetrators. Glass spheres carry an electronic vacuum gauge to ensure spheres are well sealed prior to deployment. |