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Signal processing of diurnal and semidiurnal variations in radon and atmospheric pressure: A new tool for accurate in situ measurement of soil gas velocity, pressure gradient, and tortuosity

Year: 1997
Type: article
Abstract: Signal processing of diurnal and semidiurnal variations of both atmospheric pressure and radon concentration in soil gases is shown to be useful for estimating soil gas transport parameters. The two daily‐cycle peaks at 12‐ and 24‐hour periods in the Power Spectral Density (PSD) of atmospheric pressure seem to be present everywhere on Earth's surface, and it is the effect of these regular pressure variations on the radon concentration in soil gases that makes it possible to determine three soil gas transport parameters which can be used to estimate real gas velocity; i.e. tortuosity τ, the ratiok/nbetween intrinsic permeability and effective porosity (that part of porosity involved in gas transport), and the pressure gradient α. The parameterskandncan be determined independently if the gas flux at the surface is measured at the same time. The method is robust, representative, and accurate: since it allows reliable estimation of transport parameters, it can provide relevant information about the depth of the radon source and the time it takes for information to reach the surface when radon bursts occur at depth. Radon is an appropriate soil gas tracer because it exists in all soils. Moreover, the measurement of radon concentration requires only passive sensors that do not hamper the rising gas column. Gas flux data obtained in Andalusia, Spain, in connection with mineral exploration are processed as examples. Determining the complete set of transport parameters helps in the interpretation of recorded radon outbursts, which are found to be correlated with regional seismic activity.
DOI: 10.1029/97jb00971
Language: English
Subfield: Radiation
Open Access status: bronze
OpenAlex ID: W1988205643
FWCI: 2.035
Cites: 26
Cited by: 71
Related to: 10