Velocity Calculation

Use the Velocity Calculation option (Geosoft.uxo.gxnet.dll(Geosoft.GX.UXO.UceVelocity;Run)*) from the Data Preparation > QC QA Tools menu to calculate the speed at which the operator collected the survey data given active database coordinates and time channel.

  • UXO Land extension:
    •  Data Preparation > QC QA Tools
  • UXO Marine extension:
    • UXO - Marine Grad > QC QA Tools
    • UXO - Marine Mag > QC QA Tools

Velocity Calculation dialog options

Current database

The current database name and location is provided.

Hover over the name until a tooltip appears: the full path of the current database file is displayed.

Time channel

The channel containing the time stamp. The time should be in (decimal) hours.

Script Parameter: UCEVELOCITY.TIMECH

Velocity unit

Specify the desired output velocity units. Select from: Mi/h, Km/h, m/sec, ft/sec, or knots.

Script Parameter: UCEVELOCITY VUNIT

Maximum velocity

Specify the maximum velocity at which the data should have been collected.

Script Parameter: UCEVELOCITY.MAX_VELOCITY_RANGE

Minimum velocity

Specify the minimum velocity at which the data should have been collected.

Script Parameter: UCEVELOCITY.MIN_VELOCITY_RANGE

Create a velocity map

Check this option to automatically generate an output velocity map.

Script Parameter: UCEVELOCITY.CREATEMAP

Application Notes

Use the Velocity Calculation test to verify that the data acquisition speed was acceptable. The dummy data points and the stationary readings are ignored.

Based on how the data is collected, the reported velocity at each measurement can be a very good indicator of poor performance during data acquisition. For example, if the survey design and anomaly selection criteria are based on given sample spacing, then the anomalies could go undetected if the data sampling rate is not increased to account for field data collected at higher speeds. The speed of data collection may also be used to verify that the anomaly selection is properly positioned. The velocity test can also be used to find positioning errors in the data. In addition, if the line & fiducial method is used, relatively small velocity jumps for any segment of the data are probably the result of a bad fiducial mark in the data, or a fiducial may have been missed altogether.

In the current database, the following channels are created:

  • Velocity: the survey speed, or velocity in the specified units.
  • Flag_VelocityAbove and Flag_VelocityBelow: indicate where the survey velocity was either above or below the specified thresholds. These channels can be used as 'Mask' channels: the channel values are set to "1" when velocity thresholds (minimum velocity & maximum velocity) are exceeded; otherwise are populated with dummy values ("*").
  • Point2Point: the distance between consecutive survey point. This will have the same units as the database coordinate (X,Y) channels.

A summary of the results are saved in the Process Report, and (if selected in the UXO Land Setup Parameters) the QC Report and DID database; see the DID Database section below.

You may optionally generate a velocity map. On this map, stations where the velocity is above the maximum are displayed in red, and the ones below the minimum are in blue. Statistics of the survey velocity are shown in the map legend.

DID Database

When using the UXO Land extension, you can choose to populate a US Army Corps of Engineers Data Item Description (DID) database. When OK is clicked, the following information will be exported to the Speed_Table table in the DID database if the database has been defined in the Setup Parameters dialog:

GX Parameter

Table Column

Comment

Current database

Dataset_ID

Name of the Geosoft database

Minimum velocity

Min_Speed

Min velocity from Velocity channel

Maximum velocity

Max_Speed

Max velocity from Velocity channel

 

Mean_Speed

Average velocity from Velocity channel

 

StdDev_Speed

Standard deviation of velocity values from Velocity channel

 

Percent_Pass

Percentage of the points within the acceptable range

 

Speed_Map_ID

Name of map if reported using UX-Process Velocity Calculation tool, if specified.

*The GX tool will search in the "gx" folder. The GX.Net tools, however, are embedded in the Geosoft.uxo.gxnet.dll located in the bin folder. If running this GX interactively, bypassing the menu, first change the folder to point to the bin folder, then supply the GX.Net tool in the specified format.