Processing Parameters
Use the Gravity > Processing Parameters menu option (GRPARM GX) to view and modify the gravity project parameters.
If the current database is a "single survey database" (i.e., data is imported from a single gravity instrument dump file or from a single "day" survey file), you will be presented with the Survey Parameters dialog. Otherwise, the Global Survey Parameters dialog will display. The Survey Parameters dialog includes survey specific parameters together with "global" parameters that apply to the entire project.
Survey Parameters dialog options
Database |
If the current database is a survey database, this entry simply displays the name of the database for your information. Script Parameter: GRAVRED.SURVEY_DATABASE |
Source file |
The name of the original source data file. Script Parameter: GRAVRED.FILE |
Survey date |
The survey date. Script Parameter: GRAVRED.DATE |
Operator |
The instrument operator. Script Parameter: GRAVRED.OPERATOR |
Instrument |
The instrument ID, which is the instrument name or number which designates a particular instrument. Script Parameter: GRAVRED.INSTRUMENT |
The instrument scale factor if you are not using a calibration file. If you are using a calibration file, this entry must be blank. Script Parameter: GRAVRED.INSTRUMENT_SCALE |
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OR scale factor file |
The name of an instrument scale factor calibration file. If you are using a single scale factor, this field must be left blank. See the GRCALIB GX for information on how to create a calibration scale factor file. Script Parameter: GRAVRED.INSTRUMENT_SCALE The script parameter can either be a calibration file name or a scale factor. If the setting is a number, it is assumed to be a scale factor.
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Hours to GMT (+ in W) |
This is the time difference between the time recorded in the survey database and GMT. This is a positive number in the Western hemisphere. If this field is left blank, no tide correction is applied. Script Parameter: GRAVRED.GMT_DIFFERENCE |
Global Survey Parameters dialog options
Base station database |
The name of the database that contains base station information. See the GRBASEDB GX topic for information on the base station database. Script Parameter: GRAVRED.BASE_DATABASE |
Location database |
The name of the database that contains location information. See the GRXYEDB GX for information on the base station database. Leave this entry blank if there is no location database, and the location data is already entered into the gravity survey database. The location data, if specified, will be merged into the survey database as part of the drift correction. The longitude & latitude of each station are used to calculate the gravity earth tide correction. Script Parameter: GRAVRED.LOCATION_DATABASE |
Latitude correction |
Select a gravity latitude formula from the list.
The first time the latitude correction is executed, the five formulas defined using Oasis montaj expressions are saved in the file "Gravity_Latitude.lst" located in the folder %USERPROFILE%\Documents\Geosoft\Desktop Applications \etc. If you would like to provide alternate equation(s), append them in the "Gravity_Latitude.lst" file. For syntax details, see the Application Notes section under the Latitude Correction topic.Script Parameter: GRAVRED.FORMULA |
Free-air correction |
Select an elevation (free-air) correction formula from the list. The elevation correction formulas are defined using Oasis montaj expressions (the full ellipsoid expression as a function of height and latitude from Heiskanen and Moritz (1967), and the constant gradients 0.308596 mGal/m and 0.3086 mGal/m) and are stored in a file named "Gravity_Free_Air.lst" located in the folder %USERPROFILE%\Documents\Geosoft\Desktop Applications \etc. You can add other formulas by editing this file. For syntax details, see the Application Notes section under the Free Air Anomaly topic. Script Parameter: GRAVRED.FREE_AIR |
Earth density |
The density of the earth in g/cm³ for calculating the Bouguer correction. Script Parameter: GRAVRED.DENSITY_EARTH |
Water density |
The density of water to be used for the Bouguer correction for gravity readings over water (on ice or marine surveys). The density of fresh water is 1.0 g/cm³ ; the density of salt water ranges from 1.02 to 1.07 g/cm³. The "Water" channel is assumed to contain the depth of water below the gravity station for calculating the water correction, which is only applied if a "Water" channel exists. Script Parameter: GRAVRED.DENSITY_WATER |
Ice density |
The density of ice to be used for the Bouguer correction for gravity readings on ice. The density of freshwater ice is 0.97 g/cm³ and varies for sea water. The "Ice" channel is assumed to contain the thickness of ice below the gravity station for calculating the ice correction, which is only applied if an "Ice" channel exists. The depth of "Water" must include the "Ice" thickness. Script Parameter: GRAVRED.DENSITY_ICE |
Survey type |
The gravity survey types provided are:
Script Parameter: GRPARM.SURVEYTYPE |
Application Notes
The GRPRAM GX enables you to view and change the parameters of a gravity project or of an individual gravity survey database. The changes will propagate to all applicable Gravity and Terrain Correction GXs: the associated parameters in the corresponding dialogs will default to the values set through GRPRAM GX.
This GX can be used from a script to change or set any global parameters that may be required by other GXs in a script. All global parameters begin with "GRAVRED".
To change the survey parameters of a specific file from a script, set the "GRAVRED.FILE" parameter to the file name.
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