Correlated Noise in LIGO Detectors from Schumann Resonance

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Abstract:: Schumann resonances are global peaks in the magnetic field of the earth, with a primary peak at 7.8Hz of a few pT and subsequent peaks every 6.5Hz [1]. These resonances are the result of lightning storms that occur all over the world, and as such are coherent on the scales of the distance between LIGO detectors and are time variant. Because of this being able to measure these peaks in real time and remove the parts of the spectrum that are coherent across the detectors is essential to achieving the projected noise floor in aLIGO. Here I discuss the initial the magnetic field measurements made around the LIGO Livingston and Hanford Observatories (LLO and LHO) as well as the techniques used to identify and/or remove local external sources of magnetic noise from the magnetic spectra. In addition I examine the properties of the Schumann resonances near LLO and LHO and compare their strength to the noise floors of current and (potential) future magnetometers. Finally I speculate on the potential effectiveness of using subtraction and/or wiener filtering to clean the on site magnetometer channels at LLO and LHO.

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LIGO Document P1400189-v1