Hydrological signals in gravity — foe or friend?

Abstract

Although hydrological effects on gravity are known nearly as long as the influence of barometric pressure, they are not as well understood as the latter. The improvement of gravity data quality during the last years adds weight to the importance of understanding the hydrological influence. Moxa observatory is one station at which studies regarding hydrological effects are carried out. From soil moisture, water level and meteorological observations the effects of different hydrological contributors including snow can be modelled and compared to the gravity residuals of the superconducting gravimeter (SG). The total peak-to-peak amplitude amounts to 35 nm/s 2. Contributions from the various areas around the observatory partly compensate due to the hilly morphology. The comparison between residuals and computed total hydrological effect yields a good agreement, but also shows that not all hydrological influences have been taken into account. A significant additional hydrological influence is due to the hill flank near the SG.Besides the possibility of giving an additional constraint to water balance computations, gravity observations might become of interest to hydrologists studying interflow processes. A local gravity network was established around Moxa observatory in order to find out whether slow, e.g. seasonrelated hydrological changes or large-scale fluctuations as caused by snow melt can be detected by repeated gravity measurements. From the six campaigns carried out so far a trend becomes visible: Wet conditions lead to a decrease in the gravity differences between observation points at the foot of the hill and on the upper part of the hill flank. Dry conditions result in increased gravity differences. The changes in the differences which are in the range of several ten nm/s 2 can be explained by variations in the amount of water stored in the hill flank.

Detection of small hydrological variations in gravity by repeated observations with relative gravimeters

“…Effects in time-dependent gravity observations due to water level and soil moisture variations, precipitation events, and snow covering have been discussed for a while (e.g. Abe et al, 2006;Amalvict et al, 2004;Bonatz, 1967;Bower and Courtier, 1998;Crossley et al, 1998;Elstner, 1987;Elstner and Kautzleben, 1982;Harnisch and Harnisch, 1999;Imanishi, 2000;Kroner, 2001;Kroner et al, 2007;Lambert and Beaumont, 1977;Mäki-nen and Tattari, 1988;Meurers et al, 2007;Peter et al, 1995;Sato et al, 2006;Virtanen, 2000;Zerbini et al, 2001). They range from a few nm/s 2 to some 10 nm/s 2 (10 nm/s 2 = 1µGal).…”

“…The water masses are located above and below the level of the superconducting gravimeter and the aquifers are partially confined. The rain water partially drains off on the surface, partially percolates into the fissured rock and is partially stored in the soil layer (Hasan et al, 2006;Kroner et al, 2007). Gravity changes observed with the superconducting gravimeter turned out to be correlated with hydrological variations (Kroner, 2001).…”

Influence of temperature variations on the noise level of the data of the LaCoste and Romberg Earth tide gravity meter ET18

“…From this it follows that for future recordings of the gravity variations a constant room temperature is absolutely important to achieve a high signal‐to‐noise ratio. Thereby, the separation and analyzes of small amplitude signals like hydrological effects [ Kroner et al , 2007; Naujoks et al , 2008] or the Earth core resonance effect [ Kroner , 2002] are improved.…”

A comparison of the gravity field over Central Europe from superconducting gravimeters, GRACE and global hydrological models, using EOF analysis

“…2006; Hasan et al. 2008), although investigations around MO considered a larger radius of 1 km (Kroner & Jahr 2006; Kroner et al. 2007).…”