3.6. Batch data updates
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3.6. Batch data updates

3.6.1. Shift gravity readings time

If instrument clock or GMT Difference settings are not set properly, tidal corrections were not computed correctly. Shifting of gravity readings times is a way how to fix this problem.

Typical problem is incorrect sign set for GMT difference in the firmware of the Scintrex CG-5 gravimeter. E.g. if the survey loop was completed with the GMT difference value +2 for the survey in Eastern Europe instead of the correct value of -2, all readings have to be shifted 4 hours backwards.

[Caution]Caution

GMT difference sign in the Scintrex CG-5 firmware is opposite to the sign used in BlueWhaleProcessing Project Properties settings. BlueWhaleProcessing CG-5 import procedure converts the GMT difference correctly. Internally, BlueWhaleProcessing stores all time data in GMT.

To shift gravity readings time of a single loop by a given number of hours:

  1. When desired loop is selected (highlighted) in the Projects window, click the Shift gravity readings times icon or select Tools - Shift gravity readings times from the main menu.

    Shift readings time

  2. Input required time shift in hours, e.g. -4 or 3.3333338

    Positive value means forward shift, negative value means backward shift.

  3. Press Shift button.

  4. Save, close and reopen the project when finished with time shifting.

To shift readings for the entire project, highlight the project item when opening the Shift readings time dialog.

BlueWhaleProcessing can try to estimate proper time shift based on repeated readings from the selected loop.

To estimate time shift from repeated readings, select the loop which should be used for time shift estimation, open the Shift readings time dialog and press Find optimal time shift button.

Output window shows computation progress. The best time shift is presented in the topmost line. When the estimation is finished, loop is shifted back to the initial state.

Running time shift computation can be stopped at any moment by pressing the Stop computation button. When the button is pressed, current computation step is finished and the loop is shifted back to the initial state. Do not close the Shift readings time dialog while the computation is not completely stopped yet.

[Note]Note

Searching for optimal time shift can take a reasonable amount of time.

Check coordinates of base stations used in the processed loop before running time shift determination procedure.

Time shift determination procedure needs reasonable amount of repeats for proper operation. Overnight drift test with the instrument sited on a base continuously registering is an optimal case.

Maximum time shift which can be determined by the automatic otpimal time shift determination procedure is +/- 6 hours.

3.6.2. Group readings selection

When a new gravity loop is imported into the BlueWhaleProcessing project, repeated readings at the same station occupation are ignored with exception of the last reading before the instrument is moved to the next station. The last reading is expected to be the most acceptable by the operator and this reading is selected for further processing.

Selection of individual readings can be changed in the Loop table. In addition, all readings of a gravity loop can be processed by group readings selection procedure.

To change selection for all readings of a loop:

  1. Select (highlight) the required loop in the Projects window.

  2. Click the Group select readings icon or select Edit - Group select readings from the main menu.

    Shift readings time

  3. Choose desired action in the dialog:

    Select the last reading at each station (default)

    This option behaves similarly to the selection after loop data import. The last reading for each station occupation is selected.

    Any previously selected readings reamin selected when this option is processed. If it is not the required behavior, clear all selections first before using this option.

    Unselect all readings

    When this option is processed, all readings of the selected loop are unselected.

    Select last reading and readings in interval...

    For this selection, first of all the last reading at a station occupation is selected. As the next step, all readings of this occupation are scanned in reverse order until interval between selected and current reading exceeds provided limit in minutes. If such a reading is found, it is selected and backward scanning continues until all readings for the occupation are exhausted.

    This procedure is suitable e.g. for processing of an overnight drift loop test. When the instrument is sited on a base registering in an infinite loop, group selection of readings with a given interval can be helpful for further drift processing, reporting and plotting.

  4. Click the Proceed! button to start the selected action.

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3.5. Import gravity data from a text dump Home Chapter 4. Work with lines and stations