5 research outputs found
Atmospheric Gravity Perturbations Measured by Ground-Based Interferometer with Suspended Mirrors
A possibility of geophysical measurements using the large scale laser
interferometrical gravitational wave antenna is discussed. An interferometer
with suspended mirrors can be used as a gradiometer measuring variations of an
angle between gravity force vectors acting on the spatially separated
suspensions. We analyze restrictions imposed by the atmospheric noises on
feasibility of such measurements. Two models of the atmosphere are invoked: a
quiet atmosphere with a hydrostatic coupling of pressure and density and a
dynamic model of moving region of the density anomaly (cyclone). Both models
lead to similar conclusions up to numerical factors. Besides the hydrostatic
approximation, we use a model of turbulent atmosphere with the pressure
fluctuation spectrum f^{-7/3} to explore the Newtonian noise in a higher
frequency domain (up to 10 Hz) predicting the gravitational noise background
for modern gravitational wave detectors. Our estimates show that this could
pose a serious problem for realization of such projects. Finally, angular
fluctuations of spatially separated pendula are investigated via computer
simulation for some realistic atmospheric data giving the level estimate
10^{-11} rad/sqrt(Hz) at frequency 10^{-4} Hz. This looks promising for the
possibility of the measurement of weak gravity effects such as Earth inner core
oscillations.Comment: 13 pages, 4 pigures, LaTeX. To be published in Classical and Quantum
Gravit
Geophysical studies with laser-beam detectors of gravitational waves
The existing high technology laser-beam detectors of gravitational waves may
find very useful applications in an unexpected area - geophysics. To make
possible the detection of weak gravitational waves in the region of high
frequencies of astrophysical interest, ~ 30 - 10^3 Hz, control systems of laser
interferometers must permanently monitor, record and compensate much larger
external interventions that take place in the region of low frequencies of
geophysical interest, ~ 10^{-5} - 3 X 10^{-3} Hz. Such phenomena as tidal
perturbations of land and gravity, normal mode oscillations of Earth,
oscillations of the inner core of Earth, etc. will inevitably affect the
performance of the interferometers and, therefore, the information about them
will be stored in the data of control systems. We specifically identify the
low-frequency information contained in distances between the interferometer
mirrors (deformation of Earth) and angles between the mirrors' suspensions
(deviations of local gravity vectors and plumb lines). We show that the access
to the angular information may require some modest amendments to the optical
scheme of the interferometers, and we suggest the ways of doing that. The
detailed evaluation of environmental and instrumental noises indicates that
they will not prevent, even if only marginally, the detection of interesting
geophysical phenomena. Gravitational-wave instruments seem to be capable of
reaching, as a by-product of their continuous operation, very ambitious
geophysical goals, such as observation of the Earth's inner core oscillations.Comment: 29 pages including 8 figures, modifications and clarifications in
response to referees' comments, to be published in Class. Quant. Gra