Planetary seismology-Expectations for lander and wind noise with application to Venus

摘要

The amplitudes of seismic signals on a planetary surface are discussed in the context of observable physical quantities - displacement, velocity and acceleration - in order to assess the number of events that a sensor with a given detection threshold may capture in a given period. Spacecraft engineers are generally unfamiliar with expected quantities or the language used to describe them, and seismologists are rarely presented with the challenges of accommodation of instrumentation on spacecraft. This paper attempts to bridge this gap, so that the feasibility of attaining seismology objectives on future missions - and in particular, a long-lived Venus lander - can be rationally assessed. For seismometers on planetary landers, the background noise due to wind or lander systems is likely to be a stronger limitation on the effective detection threshold than is the instrument sensitivity itself, and terrestrial data on vehicle noise is assessed in this context. We apply these considerations to investigate scenarios for a long-lived Venus lander mission, which may require a mechanical cooler powered by a Stirling generator. We also consider wind noise: the case for decoupling of a seismometer from a lander is strong on bodies with atmospheres, as is the case for shielding the instrument from wind loads. However, since the atmosphere acts on the elastic ground as well as directly on instruments, the case for deep burial is not strong, but it is important that windspeed and pressure be documented by adequate meteorology measurements.