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Levelogger User Guide - Software Version 3.4.0 or Higher
Page 49
A second important element of Barometric efficiency is time lag – the time
differential between a unit change in barometric at the surface to the time
of transmission of that change to the aquifer. Calculating general barometric
efficiency should not be done on a single barometric event, but rather on a
statistically significant number of events. As a result, it may take a month or
more of submerged Levelogger and Barologger data to determine barometric
efficiency and time lag. As Barometric pressure fluctuates over time in excess
of 60 cm water column equivalent pressure and as barometric efficiency can be
such an important factor in accurately monitoring groundwater levels, it is vital
that barometric compensation of the Levelogger data be performed.
Barometric efficiency and time lag cannot be determined with vented pressure
transducers in which barometric efficiency is assumed to be 100% no time lag.
The inherent error these assumptions can cause in the incumbent data can be
quite significant. The absolute pressure method used in the Levelogger and
Barologger provide the user with the data necessary to determine barometric
efficiency. If a barometric efficiency value has been determined from the
Levelogger and Barologger data, that value can be applied to Barologger
data in the Compensation Wizard. Application of this feature can produce
net groundwater level data of an accuracy that cannot be produced by vented
transducers.
Wells puncturing an aquifer have a negligible to non-existent effect on directly
transmitting barometric changes to the larger aquifer. Barometric pressure is
transmitted through overlying layers. To obtain the best and most accurate long
term water level readings from Leveloggers, the user must first understand how
the Levelogger calculates a depth of water above the transducer and second
whether barometric efficiency should be considered in barometric compensation.
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