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Berger, J, Davis P, Widmer‐Schnidrig R, Zumberge M.  2014.  Performance of an optical seismometer from 1 μHz to 10 Hz. Bulletin of the Seismological Society of America. 104:2422-2429.   10.1785/0120140052   AbstractWebsite

We compare the performance of four different instruments that measure the vertical component of motion of an inertial mass—an STS1 seismometer, an STS2 seismometer, a superconducting gravity meter, and an optical seismometer—operating inside the mine at the Black Forest Observatory near Schiltach in southwest Germany. Simultaneous, collocated operation of these sensors offers an opportunity to test the calibration, response, and performance of each instrument. We estimate noise floors from the tidal bands to 10 Hz. We note small nonlinearities in the suspension of the STS1, which are normally suppressed by analog signal processing and feedback or, in the optical version, by digital signal processing alone. The results demonstrate that the optical seismometer utilizing an STS1 suspension can provide observatory‐quality data over a bandwidth from tidal frequencies to at least 10 Hz and over a large dynamic range.

Faller, JE, Rinker RL, Zumberge MA.  1979.  Plans for the Development of a Portable Absolute Gravimeter with a Few Parts in 109 Accuracy. Tectonophysics. 52:107-116.   10.1016/0040-1951(79)90212-9   AbstractWebsite

Successful development of a few parts in 109 portable g apparatus (which corresponds to a height sensitivity of about 1 cm) would have an impact on large areas of geodynamics as well as having possible application to earthquake prediction. Furthermore, the use of such an instrument in combination with classical leveling or extraterrestrially determined height data would yield information on internal mass motions. The plans for the development of such an instrument at JILA using the method of free fall will be given. The proposed interferometric method uses one element of an optical interferometer as the dropped object. Recent work has resulted in substantial progress towards the development of a new type of long-period (T > 60 sec) suspension for isolating the reference mirror (corner cube) in the interferometer. Improvements here over the isolation methods previously available, together with state-of-the-art timing and interferometric techniques, are expected to make it possible to achieve a few parts in 109 accuracy with a field-type instrument.

Faller, JE, Rinker RL, Zumberge M.  1978.  Plans for the development of a portable absolute gravimeter: A tool for studying non-tidal variations in gravity. Boll. Geofis.Teor. Appl. 20:355-362. Abstract
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Chave, AD, Zumberge MA, Ander ME, Hildebrand JA, Spiess FN.  1987.  Polar Ice Test of the Scale Dependence of G. Nature. 326:250-251.   10.1038/326250b0   AbstractWebsite
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Zumberge, MA, Rinker RL, Faller JE.  1982.  A Portable Apparatus for Absolute Measurements of the Earths Gravity. Metrologia. 18:145-152.   10.1088/0026-1394/18/3/006   AbstractWebsite

We have developed a new and portable apparatus for making absolute measurements of the acceleration due to the Earth's gravity. We use the method of free fall, and interferometrically determine the acceleration of a freely falling cube corner. In the design and development of this instrument, particular attention was paid to those aspects which would affect its performance in the field. The resulting instrument, we believe, provides a viable new tool for the study of tectonic motions. The system is very small; it can be transported in a small van and requires only two hours for assembly. A high rate of data acquisition is available; if necessary, a single measurement can be made every two seconds. Further, we have made a concerted effort to detect and (we hope) eliminate systematic errors. The results of extensive tests indicate that the achievable accuracy for g is about six parts in 109. This instrument therefore provides a sensitivity to vertical motions (e.g., of the Earth's crust) as small as 2 cm.

Zumberge, MA.  1997.  Precise optical path length measurement through an optical fiber: Application to seafloor strain monitoring. Ocean Engineering. 24:531-542.   10.1016/s0029-8018(96)00029-7   AbstractWebsite

An optical tiber strainmeter intended for measuring tectonic strains on the seafloor is under development. In this instrument, an optical fiber is stretched between two points fixed to the ocean bottom; relative displacement of these points causes a change in the elongation of the fiber. This associated change in optical path length is monitored by an electronic distance meter. The dominant sources of noise in determining the optical path length of the fiber stem from the dependence of the fiber's index of refraction on both wavelength and temperature. In a 50 day long experiment performed in the shallow ocean, a test fiber was installed along a 210 m long baseline on the bottom. The RMS Variation in length was 5 mm except for two displacements of order 10 cm caused by known effects. (C) 1997 Elsevier Science Ltd.

Zumberge, M, Alnes H, Eiken O, Sasagawa G, Stenvold T.  2008.  Precision of seafloor gravity and pressure measurements for reservoir monitoring. Geophysics. 73:WA133-WA141.   10.1190/1.2976777   AbstractWebsite

Changes with gravity over time have proven to be valuable for inferring subsurface density changes associated with production from oil and natural gas reservoirs. Such inferences allow the monitoring of moving fluid fronts in a reservoir and provide an opportunity to optimize production over the life of the reservoir. Our group began making time-lapse seafloor gravity and pressure measurements in 1998. To date, we have surveyed six fields offshore Norway; we have made three repeat surveys at one field and one repeat survey at another. We incorporated a land-gravity sensor into a remotely operated seafloor housing. Three such relative gravity sensors mounted in a single frame are carried by a remotely operated vehicle (ROV) to concrete benchmarks permanently placed on the seafloor. Reference benchmarks sited outside the reservoir boundaries are assumed to provide stable fiducial points. Typical surveys last from a few days to a few weeks and cover from 8 to 80 benchmarks, with multiple observations of each. In our earliest surveys, we obtained an intrasurvey repeatability of approximately 20 mu Gal, but recently we have been achieving 3-mu Gal repeatability in gravity and approximately 5 mm in benchmark depth (deduced from simultaneously recorded ambient seawater pressure). We attribute the improved precision to several operational factors, including the use of multiple gravity sensors, frequent benchmark reoccupation, precise relocation and orientation of the sensors, repeated calibrations on land, and minimization of vibrational and thermal perturbations to the sensors. We believe that high-precision time-lapse gravity monitoring can be used to track changes in the height of a gas-water contact in a flooded reservoir, with a precision of a few meters.

Faller, JE, Rinker RL, Zumberge M.  1979.  Progress on the development of a portable absolute gravimeter. Bulletin d'Information. 44 Abstract
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