Automatic Barometric Compensation
Submersed Leveloggers measure total or absolute pressure (water column equivalent + barometric pressure). In order to accurately determine the true changes in water level only, barometric pressure fluctuations must be taken into account.
The simplest method to accomplish this is by the use of a Barologger suspended above high water level in one well on-site (approximate coverage is 20 miles (30 km) and within an elevation of 1000 ft (300 m)). This records ambient barometric fluctuations over time and allows quick and intuitive barometric compensation via the software wizard, using the data files from both the Barologger and any Leveloggers in the area.
|Manual Barometric Compensation
If an on-site Barologger is not available, your data can be compensated using alternate barometric data (e.g. from a local weather station).
To accomplish an accurate manual barometric compensation, the atmospheric pressure station should not be greater than 20 miles (30 km) away and within an elevation change of 1000 ft (300 m). In addition, the date and time of the barometric data should cover the range of data collected by the Levelogger.
Since most atmospheric pressure devices output barometric data in inches of Hg or kPa, the data must be converted to feet or meters of water. Then 31.17 ft or 9.50 m must be subtracted, since Levelogger Golds only record readings above that value.
Conversion from Inches of Hg to Feet of water column equivalent: Example: 30 inches of Hg:
30 Inches of Hg x 1.1330 = 33.99 – 31.17 = 2.82 feet H2O
Conversion from kPa to meters of water column equivalent: Example: 101.40 kPa:
101.40 kPa x 0.1022 = 10.36 – 9.50 = 0.86 meters H2O
* Values in red denote pressure conversion factors; consult the Levelogger User Guide to obtain common pressure conversions
Once the final calculated barometric pressure values are obtained, they are subtracted from the Levelogger data set. Since the Levelogger data can be easily exported as a .csv (comma separated value) file using Levelogger Software, all manual corrections can be performed in an external spreadsheet program, such as Excel.
In an example where the uncompensated Levelogger data is a water level of 10 ft, from the calculation above, the manual compensation for a barometric pressure 30 inches of Hg, would be: 10 ft – 2.82 ft = 7.18 ft.