Brownian Noise and Temperature Sensitivity of Long-Period Lunar Seismometers

ABSTRACT As long-period ground motion holds the key to understanding the interior of the Earth’s Moon, reducing long-period noise sources will be an essential area of focus in the design of future lunar seismometers. For the proposed Lunar Geophysical Network (LGN), the International Lunar Network (ILN) Science Definition Team specifies that an LGN enabling seismometer will need to be more sensitive than any previous seismometer at frequencies below 1 Hz. In an effort toward lowering the seismometer noise floor for lunar geophysical missions, we evaluate the 1/f Brownian noise and the temperature sensitivity of a seismometer. Temperature sensitivity of a seismometer is related to an important component of the seismometer output noise that is proportional to the temperature noise in the environment. The implications of the ILN requirement are presented in the context of the state-of-the-art InSight Seismic Experiment for Interior Structure (SEIS) Very Broad Band (VBB) planetary seismometer. Brownian noise due to internal friction was estimated for future lunar operation after accounting for the rebalance of the product of mass and distance to the center of gravity of the pendulum for the SEIS-VBB sensor. We find that Brownian noise could be a limiting factor in meeting the ILN requirement for lunar seismometers. Further, we have developed a formalism to understand the temperature sensitivity of a seismometer, relating it quantitatively to the local gravity, the thermoelastic coefficient of the spring, change in center of gravity, and the coefficient of thermal expansion of the mechanical structures. We found that in general the temperature sensitivity of a seismometer is proportional to the local gravity, and so the temperature sensitivity can be reduced when operating on a planetary body with lower gravity. Our Brownian noise and temperature sensitivity models will be useful in the design of the next generation of planetary seismometers.

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Study of characteristics of long-period ground motion response spectra by using broad-band records of the Chinese digital Seismograph Network

Acta Seismologica Sinica ◽

10.1007/s11589-998-0070-2 ◽

1998 ◽

Vol 11 (5) ◽

pp. 557-564 ◽

Cited By ~ 9

Author(s):

Su-Yun Wang ◽

Yan-Xiang Yu ◽

Hong-Shan Lü

Keyword(s):

Ground Motion ◽

Broad Band ◽

Response Spectra ◽

Motion Response ◽

Long Period ◽

Long Period Ground Motion ◽

Seismograph Network

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Improvements in seismic resolution and current limitations in the Global Seismographic Network

Geophysical Journal International ◽

10.1093/gji/ggz473 ◽

2019 ◽

Vol 220 (1) ◽

pp. 508-521 ◽

Cited By ~ 2

Author(s):

A T Ringler ◽

J Steim ◽

D C Wilson ◽

R Widmer-Schnidrig ◽

R E Anthony

Keyword(s):

Seismic Noise ◽

Broad Band ◽

Earth Tide ◽

Seismic Signals ◽

Noise Levels ◽

Noise Sources ◽

Long Period ◽

Seismic Resolution ◽

Fundamental Limitation ◽

Seismographic Network

SUMMARY Station noise levels play a fundamental limitation in our ability to detect seismic signals. These noise levels are frequency-dependent and arise from a number of physically different drivers. At periods greater than 100 s, station noise levels are often limited by the self-noise of the instrument as well as the sensitivity of the instrument to non-seismic noise sources. Recently, station operators in the Global Seismographic Network (GSN) have deployed several Streckeisen STS-6A very broad-band borehole seismometers. These sensors provide a potential replacement for the no-longer-produced Streckeisen STS-1 seismometer and the GeoTech KS-54 000 borehole seismometer. Along with showing some of the initial observational improvements from installing modern very broad-band seismometers at depth, we look at current limitations in the seismic resolution from earth tide periods 100 000 s (0.01 mHz) to Nyquist at most GSN sites (0.02 s or 50 Hz). Finally, we show the potential for improved observations of continuously excited horizontal Earth hum as well as the splitting of very long-period torsional modes. Both of these observations make use of the low horizontal noise levels which are obtained by installing very broad-band borehole seismometers at depth.

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Estimation of singly transiting K2 planet periods with Gaia parallaxes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2348 ◽

2019 ◽

Vol 489 (3) ◽

pp. 3149-3161 ◽

Cited By ~ 2

Author(s):

Emily Sandford ◽

Néstor Espinoza ◽

Rafael Brahm ◽

Andrés Jordán

Keyword(s):

Direct Measurement ◽

Free Parameter ◽

Broad Band ◽

Long Period ◽

Period Distribution ◽

Typical Period ◽

Stellar Models ◽

Host Stars ◽

Stellar Density ◽

As If

ABSTRACT When a planet is only observed to transit once, direct measurement of its period is impossible. It is possible, however, to constrain the periods of single transiters, and this is desirable as they are likely to represent the cold and far extremes of the planet population observed by any particular survey. Improving the accuracy with which the period of single transiters can be constrained is therefore critical to enhance the long-period planet yield of surveys. Here, we combine Gaia parallaxes with stellar models and broad-band photometry to estimate the stellar densities of K2 planet host stars, then use that stellar density information to model individual planet transits and infer the posterior period distribution. We show that the densities we infer are reliable by comparing with densities derived through asteroseismology, and apply our method to 27 validation planets of known (directly measured) period, treating each transit as if it were the only one, as well as to 12 true single transiters. When we treat eccentricity as a free parameter, we achieve a fractional period uncertainty over the true single transits of $94^{+87}_{-58}{{\ \rm per\ cent}}$, and when we fix e = 0, we achieve fractional period uncertainty $15^{+30}_{-6}{{\ \rm per\ cent}}$, a roughly threefold improvement over typical period uncertainties of previous studies.

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