Professor John Orcutt is the Director of the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at the Scripps Institution of Oceanography in La Jolla. He has conducted research in marine seismology using autonomous seafloor instruments for more than 25 years and has designed and developed a number of autonomous seismometers and hydrophones. Recent programs have included the installation of a broadband seismograph (with Woods Hole Oceanographic Institution) in a borehole south of Hawaii and the development of a new instrument termed Low-Cost Hardware for Earth Applications and Physical Oceanography or L-CHEAPO for extended autonomous recording on the seafloor. He has published more than 115 scientific papers and is the Secretary of the Navy/Chief of Naval Operations Oceanography Chair. He received the Ewing Medal from the American Geophysical Union and the U.S. Navy and is currently the General Secretary of the American Geophysical Union. He co-Chairs the Global Working Group of the Deep Earth Observatories on the Seafloor (DEOS) program which is seeking to establish as many as fifty independent ocean observatories around the earth for making geophysical and oceanographic observations.
Today, many fundamental scientific questions in the ocean sciences require the measurement of variations in physical, chemical, biological and geological processes on time scales ranging from seconds to decades, as well as a synoptic characterization of the these processes on a global scale. Traditionally, oceanography has relied upon an expeditionary approach with single ships visiting limited regions for limited times. In order to understand transients and change, however, it has become necessary to develop observatories, which operate continuously both for change detection and for improving the signal-to-noise ratio of many measurements. These "ocean observatories" will include sensors in the water column, and on or beneath the seafloor.
We envision a hierarchical system of observatories, which extend from long-term, high-quality, intensively maintained global observatories to shorter-term, portable observatories. The base of the hierarchical system would comprise a large number of portable, autonomous, non-telemetering instruments which would collect time-series data in studies where real-time access to data and/or remote instrument control are not operational requirements.
The infrastructure for seafloor observatories will consist of a set of seafloor junction boxes connected to a series of cables running along the seafloor to individual instruments or instrument clusters. The junction box, with undersea mateable connectors, provides a source of power to the instruments, and a means of transmitting two-way communications to and from the instruments. Depending upon proximity to shore and other requirements, the junction box is either terminated by a long dedicated fiber-optic cable to shore, or by a shorter cable to a surface buoy. For the surface buoy to have equivalent functionality with a shore-based cable, it must provide power and telemetry.
Ocean observatories share many of the problems encountered in the Arctic and Antarctica; power supply and communications, in particular. On the other hand, data storage and packaging are no longer problems and temperatures in the deep ocean, although slightly above freezing, don't present problems for data storage and have a limited impact on battery efficiency. Communications are a particularly important issue; our experiences with global seismic and GPS observatories on land have pointed to the fundamental importance of near-real-time communications in data delivery and the maintenance of the observatory. When attached to a subseafloor cable, communications can be extended to extremely high bandwidths. However, in most cases the use of buoys and the reliance on commercial satellite communications greatly restricts bandwidth and emphasizes the importance of data compression and communications efficiency. While commercial LEO systems may provide a key in the future, current systems are severely limited and we rely a great deal on directional antennae and satellites such as those used by Inmarsat. The high data rates characteristic of seismic data and even higher rates associated with multichannel acoustic arrays place a high premium on effective communications.
On land, and particularly on the seafloor, reliability is extremely important in order to reduce maintenance costs. The electronics costs for remote systems on the seafloor are now significantly less than the pressure enclosures and it has become important to adopt schemes used in the past only on spacecraft (e.g. redundancy and duplex communications). This, and the common communications problem of squeezing massive quantities of data through a limited bandwidth, provide many opportunities for collaboration in coming years.
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Last modified on 3/11/00 by Maggi Glasscoe (Maggi.Glasscoe@jpl.nasa.gov)
