Sensor Data Noise

Use the Sensor Data Noise option (geogxnet.dll(Geosoft.GX.AirborneQC.SensorDataNoise;Run)*) from the Airborne QC menu to identify noise in the data by calculating the fourth differences between values in a channel.

Sensor Data Noise dialog options

Input database file

Select the database from which you wish to calculate the 4^th difference values. This field is auto-populated with the name of the active database.

Data channel

Select the input data channel from which the fourth differences will be calculated.

Script Parameter: QCNOISE.CHAN

4^th difference tolerance

Specify the 4^th difference tolerance. See the Application Notes below for further details.

Script Parameter: QCNOISE.TOL

Normalize differences

By default, the normalized fourth differences are calculated: these are equal to the fourth differences divided by 16.0.

Uncheck this field if you do not want to normalize the differences.

Script Parameter: QCNOISE.NORMAL [1 – Normalize, 0 – Do not normalize]

Plot results

Specify if the outcome (flight lines, flagged locations, legend) should be plotted on the current map, on a new map, or not at all:

Existing map: this is the default option. If the legend group already exists on the map ('LEGEND_QC_<database>' in the Base view), new legend items will be added to it. If this group already exists and contains a survey path ('PATH_<database>' group in the Data view), the path will not be replotted, and the Line Attributes tab in the expanded section will not be active. The Flag Attributes tab will allow you to customize the colour, thickness, and offset from the survey path of the flagged locations.
New map: the Line Attributes tab in the expanded section is active and prompts for the label size and position as well as the colour, thickness, and break on gaps of the survey path.
Do not plot: the output plot will not be generated. The two Attributes tabs are hidden.

In order to visualize multiple QC test results on the same map, flag symbols signifying data that are outside of specifications are plotted using a unique colour and offset for each QC test.

Script Parameter: QCNOISE.MAP [0 – Display on current map (default), 1 – Display on a new map, 2 – Do not plot]

Map name

Specify the name of a new or existing map on which to plot the results. The map will open in the foreground. If the map is new, you will be prompted to interactively specify the location of the legend. New information will be added to the map; the legend will indicate the line path colour as well as the colour of the flagged locations and the percentage of the survey that is not within the specifications.

When a new map is generated, the map is scaled to the input database extents, and the map projection is set to the projection of the database.

Script Parameter: QCNOISE.MAP_FILE

[More]

Flag Attributes

Color

Readings exceeding the specified tolerance are indicated by colour-coded symbols along the survey path. Select a colour for plotting these symbols. By default, this is set to orange.

Script Parameter: QCNOISE.FLAG_COLOR

Thickness

Specify the symbol size in mm. By default, it is set to 0.2.

Script Parameter: QCNOISE.FLAG_THICKNESS

Offset

Specify the symbol offset (the distance from the survey line) in mm. By default, it is set to -0.3.

A negative value will plot the symbols to the left of the survey line; a positive value will plot the symbols to the right of the survey line. Set the offset to 0 to plot the symbols on top-of-the-line path.

Script Parameter: QCNOISE.FLAG_OFFSET

Line Attributes

Colour	Select a colour for plotting the line path. By default, the colour is set to black. Script Parameter: QCNOISE.LINE_COLOR
Thickness	Specify the line thickness in mm. By default, it is set to 0.15. Script Parameter: QCNOISE.LINE_THICKNESS
Label location	Select the label position relative to the ends of the lines: End (default): the labels are displayed centered off the ends of the line Above: the labels are displayed above the ends of the lines Below: the labels are displayed below the ends of the lines None: the line labels are not plotted Script Parameter: QCNOISE.LINE_LABEL_LOCATION
Label size	Specify the label size in mm. The default is 2.5. Script Parameter: QCNOISE.LINE_LABEL_SIZE
Break on gaps>	Specify the maximum gap (in units of distance) before breaking the line. The default is 0 (no gap). Script Parameter: QCNOISE.LINE_BREAK_ON_GAPS

Application Notes

This GX assumes that the current database is the one containing the actual survey data. The database is called the survey database. If you wish to process a different database, you may browse to add it to the project or select one from the workspace list.

Quality Control Specifications and Indicators

This GX creates a channel called Flag_Noise. Fourth differences are calculated for the input channel. The difference values outside the range defined by +/- the specified tolerance will have the value of 1 placed in the Flag_Noise channel (differences with a dummy result in a dummy). The sign of the flag is the sign of the 4^th difference. Values within the tolerance range will be flagged with a 0.

Indicator Definition

0	Noise level is acceptable.
±1	Noise level exceeds the specified limit.

*The GX.NET tools are embedded in the geogxnet.dll file located in the \Geosoft\Desktop Applications\bin folder. To run this GX interactively (outside the menu), first navigate to the bin directory and provide the GX.NET tool in the specified format. See the Run GX topic for more guidance.