Data processing: measuring – calibrating – or testing – Measurement system – Accelerometer
Patent
1997-02-26
1999-07-13
Barlow, John
Data processing: measuring, calibrating, or testing
Measurement system
Accelerometer
702150, 702153, 702159, 73178H, 73178R, 342424, G01V 716
Patent
active
059240563
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device and a method for observing gravitation in accordance with the preambles of the independent claims.
The so called gravimetry or measurement of gravitation has to be classified as a special field of measurement technology, essential for the determination of the gravity field of the earth, thereby for regional and global geodesy, geology or geophysics including exploration, satellite orbit determination, precise navigation especially by inertial navigation instruments etc.
Devices for observing gravity earlier were based on the principle of pendulum observations, today either on the principle of precise tracking of a throw-/fall trajectory (few dm length inside a vacuum chamber) or on the principle of a spring balance (constant mass, determination of force). They also may be assigned to the more general class of accelerometers, as vice versa gravimeters may be seen as accelerometers particularly suited for gravity observations. Gravimeters also stand out from accelerometers in general by their significantly increased natural period. The predominant number of accelerometers or gravimeters, respectively, is based on the principle of a spring balance with constant mass, where frequently (and also for the accelerometers used in this case) the proof mass is kept in a null position also under varying accelerations by a feedback system of a (e.g., capacitive) pickoff and a (e.g., inductive) restoring force; the necessary current is a measure of the acceleration.
The pertinent state of the art is published particularly in TORGE, W.: Gravimetry, DeGruyter, Berlin, New York 1989, and in a conference proceedings volume, COLOMBO, O.(ed.): From Mars to Greenland: Charting Gravity with Space and Airborne Instruments, Symposium no 110, Springer Verlag, New York etc. 1991.
In explanation of a few terms used: of instrumental performance in the sense of a mean error in a usual modeling. For the description of the quality of a solution found for the gravitational field of the earth sought after the term accuracy is dangerous: A quantitative description of the gravitational field of the earth always is the result of many individual observations and a subsequent evaluation, leading somehow to a surface function. The characterizing of the said surface function by an accuracy value would neglect, to what area the said value refers. Because for the mean value of a larger area more values are available in general, a better accuracy value--i.e., a smaller mean error--would be in place for a given task; this--however--contradicts the plausible notion. For this case, the term of resolution is more suitable. Although also not sharply defined, one may imagine the following: The surface function may be approximated by means of e.g., a two dimensional trigonometric series, i.e., by a series of waves of graded wavelengths, in both directions. The wave with the shortest wavelength with a significantly nonzero amplitude corresponds to the resolution. This interpretation also is not totally strict, because e.g., the level of significance and the grading of the wavelength anticipated might be questioned. For our purpose, however, such a discussion is not necessary. of the gravity field. In the following the term gravitation will be preferred, because--as a matter of fact--predominantly gravitation is dealt with. `Gravitation` denotes the specific force with the unit m/s.sup.2 corresponding to the unit of an acceleration. It is reminded, however, that the so called gravity is composed of the gravitation and the centrifugal acceleration because of the rotation of the earth. The latter amounts to a maximum of 5% of gravitation. respectively, because of the inertia, even if the near gravitational masses would be removed. A space (thought as empty in the near vicinity) with a reference frame with respect to which motion changes can be observed, is an inertial space. reference frame it is necessary to know not only its position, but also its direction. It may be named orientation. It is characterized by the an
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"Carbone Gravimetry--Merely a Trial or a Method for Determining Gravity on a Profile?"; K. Hehl et al.; IEEE Position Location and Navigation Symposium; Apr. 11, 1994; pp. 376-380.
Boedecker Gerd
Leismuller Franz
Neumayer Karl Hans
Barlow John
Boedecker Gerd
Vo Hien
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