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We present measurements of an optomechanical accelerometer for monitoring low-frequency noise in gravitational wave detectors, such as ground motion. Our device measures accelerations by tracking the test-mass motion of a 4.7 Hz mechanical resonator using a heterodyne interferometer. This resonator is etched from monolithic fused silica, an under-explored design in low-frequency sensors, allowing a device with a noise floor competitive with existing technologies but with a lighter and more compact form. In addition, our heterodyne interferometer is a compact optical assembly that can be integrated directly into the mechanical resonator wafer to further reduce the overall size of our accelerometer. We anticipate this accelerometer to perform competitively with commercial seismometers, and benchtop measurements show a noise floor reaching 82 pico-g Hz−1/2 sensitivities at 0.4 Hz. Furthermore, we present the effects of air pressure, laser fluctuations, and temperature to determine the stability requirements needed to achieve thermally limited measurements. 

We present a method to characterize the noise in ground-based gravitational-wave observatories such as the Laser Gravitational-Wave Observatory (LIGO). This method uses linear regression algorithms such as the least absolute shrinkage and selection operator to identify noise sources and analyzes the detector output vs noise witness sensors to quantify the coupling of such noise. Our method can be implemented with currently available resources at LIGO, which avoids extra coding or direct experimentation at the LIGO sites. We present two examples to validate and estimate the coupling of elevated ground motion at frequencies below 10 Hz with noise in the detector output.