Delta-g observations

 

Delta-g observations are shown in the Delta table on the network adjustment tab:

 

 

Delta-g observations (also called relative-gravity differences) must be populated (that is, copied from their respective loops to the Network Adjustment tab) using menu commands on the Adjustment menu. Delta-g's for all surveys can be populated at once, or individual surveys, or individual loops. The latter options are useful to verify that individual loops can be adjusted correctly before adjusting the entire survey or campaign.

 

Delta-g's can be unchecked to exclude them from the network adjustment. For the "none", "adjustment", or "continuous" drift methods, the start/end times, and duration between them are shown. For the Roman method, the time at which the delta-g is calculated is shown.

 

Two columns for standard deviation are shown: that calculated from the station observations and/or drift method ("Std. dev." column), and the standard deviation used in the network adjustment ("SD for adj." column). The latter can be adjusted if needed by specifying a minimum value, or multiplier (see Network adjustment options). This is helpful to avoid giving too much weight to delta-g's with very small standard deviations.

 

The standard deviation for the network adjustment ("SD for adj." column) can also be manually edited. Care should be taken with this option because the fact that the standard deviation was modified may not be obvious. The modified standard deviation will be saved with the workspace, and a record of the modification is stored in the log file. If the standard deviations are scaled after the initial adjustment, the user-modified standard deviations are also scaled.

 

If the drift-correction type is none, network adjustment, or continuous, the delta-g value can also be modified. This can be useful when troubleshooting bad observations, or hand-entering datasets. If modified, the delta-g value is shown in red.

 

The other items in the table cannot be modified. However, stations can be renamed in the tree view.

 

Before network adjustment, the Residual column shows the default value -999. After network adjustment this column shows the difference between the adjusted delta-g and the measured delta-g. Clicking the column header sorts by residual magnitude.