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Zumberge, MA, Berger J, Dzieciuch MA, Parker RL.  2004.  Resolving quadrature fringes in real time. Applied Optics. 43:771-775.   10.1364/ao.43.000771   AbstractWebsite

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 X 10(-13) m Hz(-1/2) at 2 Hz. (C) 2004 Optical Society of America.

Zumberge, MA, Ander ME, Lautzenhiser TV, Parker RL, Aiken CLV, Gorman MR, Nieto MM, Cooper APR, Ferguson JF, Fisher E, Greer J, Hammer P, Hansen BL, McMechan GA, Sasagawa GS, Sidles C, Stevenson JM, Wirtz J.  1990.  The Greenland gravitational constant experiment. Journal of Geophysical Research-Solid Earth and Planets. 95:15483-15501.   10.1029/JB095iB10p15483   AbstractWebsite

An Airy-type geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 m and 1673 m to test for possible violations of Newton's inverse square law. The experiment was done at Dye 3, the location of a Distant Early Warning Line radar dome and the site of the deepest of the Greenland Ice-Sheet Program (GISP) drill holes. Gravity measurements were made at eight depths in 183-m intervals with a LaCoste&Romberg borehole gravity meter. Prior to the experiment the borehole gravity meter was calibrated with an absolute gravity meter, and the wireline depth-rinding system used in the borehole logging was calibrated in a vertical mine-shaft against a laser geodimeter. The density of the ice in the region was calculated from measurements taken from ice cores obtained from earlier drilling observations. Ice penetrating radar was employed in order to correct the gravity data for the topography of the ice-rock interface. Surface gravity observations were made to assess the extent to which density variations in the sub-ice rock could affect the vertical gravity gradient. The locations of the gravity observation points were determined with a combination of GPS recording, first-order leveling, and EDM surveying. An anomalous variation in gravity totaling 3.87 mGal (3.87×10−5 m/s2) in a depth interval of 1460 m was observed. This may be attributed either to a breakdown of Newtonian gravity or to unexpected density variations in the rock below the ice.

Zumberge, MA, Hildebrand JA, Stevenson JM, Parker RL, Chave AD, Ander ME, Spiess FN.  1991.  Submarine measurement of the Newtonian gravitational constant. Physical Review Letters. 67:3051-3054.   10.1103/PhysRevLett.67.3051   AbstractWebsite

We have measured the Newtonian gravitational constant using the ocean as an attracting mass and a research submersible as a platform for gravity measurements. Gravitational acceleration was measured along four continuous profiles to depths of 5000 m with a resolution of 0.1 mGal. These data, combined with satellite altimetry, sea surface and seafloor gravity measurements, and seafloor bathymetry, yield an estimate of G = (6.677 +/- 0.013) x 10(-11) m3 s-2 kg-1; the fractional uncertainty is 2 parts in 1000. Within this accuracy, the submarine value for G is consistent with laboratory determinations.