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Direct effects of barometric pressure

Besides tilting the ground, the continuously fluctuating barometric pressure affects seismometers in at least three different ways: when the seismometer is not enclosed in a hermetic housing, the mass will experience a variable buoyancy which can cause large disturbances in vertical sensors. Changes of pressure also produce adiabatic changes of temperature which affect the suspension (see the next subsection). Both effects can be greatly reduced by making the housing airtight or installing the sensor inside an external pressure jacket, but then the housing or jacket may be deformed by the pressure and these deformations may be transmitted to the seismic suspension as stress or tilt. While it is always worthwile to protect vertical long-period seismometers from changes of the barometric pressure, it has often been found that horizontal long-period seismometers are less sensitive to barometric noise when they are not hermetically sealed. This may, however, cause other problems such as corrosion.



Erhard Wielandt
2002-11-08