Analysis at a Single Point

In addition to analyzing groundwater storage change averaged over a region, the GGST app can be used to perform an analysis at a single point location. This can be used to quickly generate a time series at a point of interest or in cases where a region of interest is too small to be processed using the Upload Region feature. For a point analysis, GGST finds the GRACE and GLDAS grid cells containing the selected point and returns the selected dataset time series for the cell.

Selecting a Point

Before performing a point analysis, you should first zoom in to your area of interest. You can do this using either the global view, or by selecting a region that has previously been uploaded. You should then select the desired storage component using the “Select Storage Component” option. These options will include: Total Water Storage (GRACE), Surface Water Storage (GLDAS), Soil Moisture Storage (GLDAS), and Groundwater Storage (Calculated). After selecting a component, click on the Select Point tool and then click on the map where you wish to perform a point analysis. If you are viewing a region, the selected point must be within the bounds of the region.

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After clicking on a point, a time series plot for the selected storage component at the point location appears:

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If the Time Series window is closed, it can be relaunched using the “View Time Series” button on the left.

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To perform a time series analysis at a new point, close the Time Series window and click on a new point while the Select Point tool is active.

Moving or Deleting a Point

To delete an existing point, click on the Delete tool and select the “Clear All” option.

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Exporting a Time Series

To export the data associated with a point time series, click on the menu icon in the upper right corner of the Time Series window and export to the selected format:

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When exporting a time series, the data in the time series are saved to a tabular file with columns for the date, and each component of the time series is exported as a separate column. The date column is saved in a unique format representing the number of milliseconds since January 1, 1970. This can be converted to a more typical date format using a spreadsheet formula. This process is described in the Water Table Fluctuation Method section.