A microprocessor-based ocean-bottom seismometer

For over 12 years, the Scripps Institution of Oceanography has operated a fleet of microprocessor-based ocean-bottom seismometers. These instruments free-fall to the seafloor and release their anchors and rise to the surface either at preset times or on receipt of an acoustic command. The instruments are contained in a single spherical pressure case and include geophones with a 1-Hz natural period, and differential pressure gauges responsive to acoustic signals between 0.003 and 30 Hz. Recent improvements described in detail here include the implementation of a C-44 bus 80C88 microprocessor and cassette recorders capable of storing up to 10 days of data digitized at 128 samples/sec, or 40 days at 32 samples/sec. In addition, tiltmeters have been installed in the instruments. Serial links to the processor and release timers provide for instrument checkout and the setting of time and data parameters from outside the pressure case. A portable laboratory also described here is used to prepare the instruments for deployment at sea.