In this paper, an intelligent surveillance system using sensor networks for monitoring active volcanoes has been presented. We combine sensor network system engineering with systems-on-chip ...implementation to develop a gigascale integrated surveillance system called Sensor Networks for Active Volcanoes (SNAV). We report SNAV specific science-related requirements and system-level operations for this surveillance system. We also present the SNAV system-on-chip implementation. The success of this work enables low-power, low-cost sensor networks for the intelligent surveillance systems.
Volcanic tremor, the seismic signal which is often associated with eruptions, is among the least understood phenomena in seismology. Large variations in the physical properties of volcanic rocks and ...fluids along with the complex geological structure make it difficult to obtain reliable source models. Old Faithful geyser, Yellowstone National Park, was chosen as a laboratory for studying fluid-flow-induced seismicity. The geyser's cyclic behavior on an hourly time scale, and its accessibility, make it suitable for a detailed study of seismic behavior between eruptions simultaneously with underwater pressure measurements inside the geyser.
We observe that sharp pressure pulses inside the water-column attributed to steam bubble collapse are followed by distinct seismic events, with a sharp onset and a harmonic horizontal motion whose frequency varies spatially but not temporally. A superposition of these events creates the appearance of continuous harmonic tremor. Since the pressure in the water column exhibits no sign of resonance, the harmonic motion must be caused by elastic waves reverberating in the solid medium. A near-surface soft layer is demonstrated to be a possible elastic model.
The harmonic tremor observed at Old faithful seems analogous to some examples of shallow volcanic tremor.
Seismology is the main tool for inferring the deep interior structures of Earth and potentially also of other planetary bodies in the solar system. Terrestrial seismology is influenced by the ...presence of the ocean-generated microseismic signal, which sets a lower limit on the earthquake detection capabilities but also provides a strong energy source to infer the interior structure on scales from local to continental. Titan is the only other place in the solar system with permanent surface liquids and future lander missions there might carry a seismic package. Therefore, the presence of microseisms would be of great benefit for interior studies, but also for detecting storm-generated waves on the lakes remotely. We estimated the strength of microseismic signals on Titan, based on wind speeds predicted from modeled global circulation models interior structure. We find that storms of more than 2 m/s wind speed, would create a signal that is globally observable with a high-quality broadband sensor and observable to a thousand kilometer distance with a space-ready seismometer, such as the InSight instruments currently operating on the surface of Mars.
Before deploying to the surface of Mars, the short-period (SP) seismometer of the InSight mission operated on deck for a total of 48 hours. This dataset can be used to understand how deck-mounted ...seismometers can be used in future landed missions to Mars, Europa, and other planetary bodies. While operating on deck, the SP seismometer showed signals comparable to the Viking-2 seismometer near 3 Hz where the sensitivity of the Viking instrument peaked. Wind sensitivity showed similar patterns to the Viking instrument, although amplitudes on InSight were ~80% larger for a given wind velocity. However, during the low wind evening hours the instrument noise levels at frequencies between 0.1 and 1 Hz were comparable to quiet stations on Earth, although deployment to the surface below the Wind and Thermal Shield lowered installation noise by roughly 40 dB in acceleration power. With the observed noise levels and estimated seismicity rates for Mars, detection probability for quakes for a deck-mounted instrument are low enough that up to years of on-deck recordings may be necessary to observe an event. Because the noise is dominated by wind acting on the lander, though, deck-mounted seismometers may be more practical for deployment on airless bodies, and it is important to evaluate the seismicity of the target body and the specific design of the lander. Detection probabilities for operation on Europa reach over 99% for some proposed seismicity models for a similar duration of operation if noise levels are comparable to low-wind time periods on Mars.
The NASA InSight lander successfully placed a seismometer on the surface of Mars. Alongside, a hammering device was deployed that penetrated into the ground to attempt the first measurements of the ...planetary heat flow of Mars. The hammering generated repeated seismic signals that were registered by the seismometer. These signals can potentially be used to image the shallow subsurface just below the lander. However, the frequencies excited by the hammering probe widely exceed the Nyquist frequency dictated by the seis-mometer's sampling rate. Here, we propose an algorithm to reconstruct the seismic signals beyond the classical sampling theorem. We exploit the structure in the data due to thousands of repeated, only gradually varying hammering signals as the heat probe slowly penetrates into the ground. This allows us to reconstruct signals by enforcing a sparsity constraint in a modified Radon transform domain.
PDF