Martian Ambient Seismic Noise: from the first modeling to the future data of the InSight Seismic experiment.
Abstract:The InSight NASA Discovery mission is expected to deploy a 3 axis VBB and a 3 axis SP seismometer on Mars by late september 2016. This seismic station will explore the Martian ambient noise, in addition to more classical science goals related to the detection of Marsquakes, Meteoritic Impacts and Tides.
Mars, in contrast with the Earth (with both atmosphere and ocean) and the Moon (with no atmosphere nor ocean) is expected to have ambient noise only related to its atmosphere. Mars seismic data are therefore expecting to reveal the atmospheric coupling for a different atmospheric dynamics than Earth, especially in the 0.1-1 Hz bandwidth, dominated by oceanic microseisms on Earth.
We rapidly present the expected performances of the SEIS experiment onboard InSight. This experiment is based on two 3 axis seismometers, one covering the tide and low seismic frequencies (up to 10 Hz) and a second one covering the high frequencies (from 0.1 Hz to 50 Hz). Both sensors are mounted on a sensors plateform, deployed by a robotic arm 1-2 meters from the lander and covered by thermal protection and a wind protection. The expected performances indicates that signal as low as 10**(-9) m/s**2/Hz**(1/2) will be detected in the 0.005-2 Hz bandwidth.
We then focus on the modeling of this ambient atmospheric noise.This modeling has been done not only from constraints gathered by the atmospheric sensors of previous Mars missions (e.g. Viking and Pathfinder) but also by numerical modeling of the atmospheric perturbations, both at global scale and mesoscale. Theoretical estimation of the ambient noise has then been obtained for the pressure-correlated surface loading and the stochastic excitation of surface waves, at both long and very long period (e.g. Mars hum) and at medium or short period (e.g. regional and local generated surface waves). Results shows that most of these source of ambient noise will be detected, likely during the day for those generated locally and possibly during the night for those of global origin.