Abstract
Abstract. Many geo-hazards such as earthquakes, tsunamis, volcanic eruptions, severe weather, etc., produce acoustic waves with sub-audible frequency, so called infrasound. This sound propagates from the surface to the middle and upper atmosphere causing pressure and temperature perturbations. Temperature fluctuations connected with the above mentioned events usually are very weak at the surface, but the amplitude increases with height because of the exponential decrease of atmospheric pressure with increasing altitude. At the mesopause region (80–100 km height) signal amplitudes are about two to three orders of magnitude larger than on the ground. The GRIPS (GRound-based Infrared P-branch Spectrometer) measurement system operated by the German Remote Sensing Data Center of the German Aerospace Center (DLR-DFD) derives temperatures of the mesopause region by observing hydroxyl (OH) airglow emissions in the near infrared atmospheric emission spectrum originating from a thin layer at approximately 87 km height. The GRIPS instrument is in principle suited for the detection of infrasonic signals generated by e.g. tsunamis and other geo-hazards. This is due to the fact that the infrasound caused by such events should induce observable short-period fluctuations in the OH airglow temperatures. First results obtained during a field campaign performed at the Environmental Research Station "Schneefernerhaus", Zugspitze (47.4° N, 11.0° E) from October to December 2008 are presented regarding potential sources of meteorological and orographical origin. An adequate distinction of the overlapping infrasonic signatures caused by different infrasound sources in the OH temperature record is needed for the ascription to the proper source. The approach presented here could form a contribution to a hazard monitoring and early warning system.
Highlights
Infrasound is generated by a wide variety of natural sources as e.g. earthquakes, volcanic eruptions or severe weather, and by man-made sources such as explosions, aircrafts or industrial activities
The GRIPS 5 spectrometer was deployed for this campaign to demonstrate the capability of this instrumentation to detect low frequency infrasonic signals
27 nighttime time series of up to 3000 observing hydroxyl (OH) spectra per night were recorded with a maximum temporal resolution of 15 s per spectrum
Summary
Infrasound is generated by a wide variety of natural sources as e.g. earthquakes, volcanic eruptions or severe weather, and by man-made sources such as explosions, aircrafts or industrial activities (see Gossard and Hooke, 1975; Blanc, 1985; Campus, 2004 for an overview on infrasonic sources). Beig et al, 2003, and references therein) of which many have recently formed the Network for the Detection of Mesopause Change (NDMC; http://wdc.dlr.de/ndmc) These airglow derived temperatures have been used for example for studying planetary waves with periods from days to weeks Time series of OH temperatures occasionally show signatures of periods even below 5 min if the temporal resolution of the used instrument is sufficiently high Possible sources of such small-scale signatures are infrasonic signals. Using the measurement technique of infrared spectroscopy with sufficient high temporal resolution in conjunction with a versatile signal classification algorithm, it should be possible to detect and identify the signals associated with geo-hazards such as a tsunami.
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