GMS:Observations: Difference between revisions
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{{Infobox Calibration}} | {{Infobox Calibration}} | ||
Observations can be either point observations or flow observations. | |||
==Point Observations== | ==Point Observations== | ||
The primary type of field data used in a typical calibration exercise is point observations. Point observations represent values that are measured at some location in the field. Point observations generally correspond to water table elevations measured at observation wells. However, multiple observed values can be defined at each observation point. Observation points are managed in the Map module using the [[GMS:Coverages#Coverage_Setup|''Coverage Setup'']] dialog. | The primary type of field data used in a typical calibration exercise is point observations. Point observations represent values that are measured at some location in the field. Point observations generally correspond to water table elevations measured at observation wells. However, multiple observed values can be defined at each observation point. Observation points are managed in the Map module using the [[GMS:Coverages#Coverage_Setup|''Coverage Setup'']] dialog. | ||
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<!--<math>\frac{1}{ \big( \text{Standard Deviation} \big) ^2 * \text{Group Weight} }</math>--> | <!--<math>\frac{1}{ \big( \text{Standard Deviation} \big) ^2 * \text{Group Weight} }</math>--> | ||
[[Image:observeq1.jpg]] | :[[Image:observeq1.jpg]] | ||
Note that GMS will automatically convert from an interval and a confidence to a standard deviation, or directly enter the standard deviation. | Note that GMS will automatically convert from an interval and a confidence to a standard deviation, or directly enter the standard deviation. | ||
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<!--:sd = CI/z | <!--:sd = CI/z | ||
:<math>sd = \frac{CI}{z}</math>--> | :<math>sd = \frac{CI}{z}</math>--> | ||
[[Image:observeq2.jpg]] | :[[Image:observeq2.jpg]] | ||
where sd is the standard deviation, CI is the confidence interval, and z is the the "z statistic" based on the specified confidence and the normal distribution. | where ''sd'' is the standard deviation, ''CI'' is the confidence interval, and ''z'' is the the "z statistic" based on the specified confidence and the normal distribution. Enter an interval and confidence, and the standard deviation will be computed; or enter a standard deviation and confidence, and the interval will be computed. | ||
In practical terms entering an interval (or standard deviation) and confidence is an indication of how much error | In practical terms entering an interval (or standard deviation) and confidence is an indication of how much error is believed to be associated with the observed value. | ||
The standard deviation becomes important when using an inverse model. The weight assigned to each of the observations points is a function of the standard deviation. This weight is used in the objective function that the inverse model tries to minimize. An observation point with a small standard deviation will have a greater influence on the objective function than a point with a large standard deviation. | The standard deviation becomes important when using an inverse model. The weight assigned to each of the observations points is a function of the standard deviation. This weight is used in the objective function that the inverse model tries to minimize. An observation point with a small standard deviation will have a greater influence on the objective function than a point with a large standard deviation. | ||
Enter an interval (or standard deviation) and confidence in the [[GMS:Feature Objects#Feature Object Properties|''Properties'']] dialog. Although these values are rarely quantified the following examples may prove helpful. | |||
For example, if having the following set of head measurements for one observation well: | |||
{| style="text-align:center; border: 1px solid gray; padding: 5px;" | :{| style="text-align:center; border: 1px solid gray; padding: 5px;" | ||
!width="150"|Date | !width="150"|Date | ||
!width="75"|Head | !width="75"|Head | ||
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|} | |} | ||
The mean of the data is 52.17 and the standard deviation is 3.25. | The mean of the data is 52.17 and the standard deviation is 3.25. Enter this standard deviation and a confidence of 95%. | ||
Many times | Many times there is not this much data available. Usually there will only be one measured value. In this case use engineering judgement to estimate an interval or standard deviation. For example, if there is a single head measurement of 45.7 ft and it is believed that observation is accurate to within a 1 foot. Then enter 1 foot as the interval. | ||
==See also== | ==See also== | ||
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[[Category:Calibration]] | [[Category:Calibration]] | ||
[[Category:Calibration Dialogs]] | |||
[[Category:GMS Dialogs|O]] | [[Category:GMS Dialogs|O]] | ||
[[Category:Equations|O]] | [[Category:Equations|O]] | ||
[[Category:Observations]] |