Compensating Data

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Posted: March 1, 2018
Category: Products
Tags: barLog, compensating, data, logger, water level

Many people ask “Why do I need to compensate my data?”

When using pressure transducers that measure absolute pressure, barometric pressure is a component of that measurement.  Barometric pressure is not a constant and must be subtracted from the pressure recorded to realize the actual water level.

Barometric pressure is pressure exerted by the atmosphere on the ground directly below it.  Many factors can cause a fluctuation in the barometric pressure.  Temperature changes and weather systems are the most common causes of significant barometric pressure change.  As the temperature increases, air becomes less dense lessening the barometric pressure.  Conversely, increases in humidity are accompanied by increased barometric pressure.  Meteorologists use barometric pressure models to predict the weather since changes in the barometric pressure are often a forerunner of a storm.

If you live in an area that has a significant daily temperature change, such as the American Southwest, you will have an accompanying significant barometric pressure fluctuation.  This is known as the diurnal shift and can be as much of a pressure variation as 0.30m or 12” of H2O daily.

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If you are monitoring water levels over a period of time, these barometric pressure changes will be reflected in your recorded measurements.  If you do not remove these influencing pressure variations from your data you could falsely identify a draw on your water resources.

Heron Instruments barLog , our barometric logger, will remove these barometric influences from the data recorded by your Heron Instruments dipperLog data logger with a minimum of effort or fuss.  Simply programme all the dipperLog you want to compensate with the same job number or project name as the one given to the barLog which will be used as the source of the compensating data.  

It is recommended that for best results the barLog and dipperLog all be within the same 20km area and at the same altitude.

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When it is time to download your data, simply download the barLog first.  All subsequent downloads of dipperLog pressure data with the same job number or project name will be compensated by this barLog data.  To determine whether your data has been compensated with barLog data, check the Compensation Flag in the data.  If “1” this data has been compensated with data from an associated barLog, if “0” it hasn’t.  If no barLog assigned, a constant value in the software will be used as the barometric pressure for compensation.  

 

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