Magnetic Observatories:
Many of the issues regarding the worldwide distribution of seismological stations are also important for geomagnetic observatories. Measurement of the geomagnetic field and its spatial and temporal variations is one of the most ancient environmental observations made by man. Continuous recording of the geomagnetic field commenced as early as 1845 in London and Paris. Since then, about 120 geomagnetic observatories have been or are running all over the world, most of which are concentrated in Europe.
The effort to operate a group of geomagnetic stations can only be justified by the ultimate use of the data. Measurements of the geomagnetic field are used to address a variety of scientific issues:
-
Main field models
- Main field Secular
Variation Models
- Regional Field
models
- Study of individual
magnetic events by Solar-Terrestrial community
- Magnetic Activity
Indices
- Regional
Ionospheric/Magnetospheric Studies
- Core-Mantle Boundary
Processes
- Earth Induction
Studies
- Magnetic signals
associated with Natural Hazards
Although magnetometers towed by oceanographic ships have provided numerous profiles of the total intensity of the geomagnetic field over the past three decades, there have only been a very few studies of the natural time variations of the geomagnetic (and geoelectric) fields on the sea-floor. In all such studies to-date, only the variations in time about an arbitrary reference value of the fields have been measured. No information has yet been obtained from the sea-floor of the absolute inclination and declination of the geomagnetic field with reference to the geodetic (true north) frame. Therefore, over the 70% of the earth's surface covered by the oceans, the three components of the absolute geomagnetic field in the geographical reference frame is totally unknown, a quite remarkable statement for the late 1990's. This perhaps surprising statement points out the severe bias in our observations of the near-earth environment which has lead to a fundamental problem in our understanding of several of the scientific issues listed above.
Furthermore, a wide variety of human activities in the ocean require knowledge of the geomagnetic field and more especially the direction of true (geodetic) north. While these measurements are easily obtained on land, and also on the surface of the ocean, there is no accurate and inexpensive means of doing so on the sea-floor. The construction of a system that will be readily adapted to meet a wide range of basic scientific, technological and industrial applications within the ocean environment is thus very important. Our initial application for this development is for determining the geodetic orientation of a platform equipped with a DI (magnetic declination-inclination) sensor as the basis for permanent sea-floor magnetic observatory installations. This is immediately applicable to a host of other sea-floor platforms that need to be geodetically oriented such as seismological stations, a subject of great international interest, but also has significant ramifications for deep ocean navigation and resource exploitation.
Seafloor Seismic Observatories
Colocation of Magnetic and Seismic Stations
Seismicity in the Monterey Region