Tutorials¶
This section provides links to the tutorial JupyterLab notebooks.
The examples show the necessary and common parameters passed to each function. There are other parameters available for many of the functions providing additional options. Further information can be seen in the API.
You can download any, or all, of the Jupyterlab notebooks from github and run them yourself once you have galileoQC installed and running. Once you have copied a notebook, you can modify it and use it on your own data.
The notebooks are available at the galileoQC repository.
Prepare XYZ data¶
The Geosoft XYZ data format file is commonly used in geophysics to transmit geophysical survey data in a text-readable form.
We need all the data in HDF5 geoWhizz format because all the QC functions expect that format. (More on the geoWhizz format here.)
For three of the example data sets (Eastern Victoria gravimetry, Melbourne magnetometry, and Vinton Dome), the field data are supplied in Geosoft XYZ format. This tutorial demonstrates the preparation of these XYZ data files as geowhizz HDF5 files for later use in quality control checks.
The appropriate Prepare_* tutorial should be run before running any of the other tutorials that utilise the relevant data.
Prepare ASEG-GDF2 data¶
One of the example data sets is supplied in ASEG-GDF2 format, a geophysical standard format used to transmit geophysical survey data in a text-readable form[1]. This tutorial demonstrates the preparation of these data as a geowhizz HDF5 files for quality control checks.
For this example we are using the data from the Kauring airborne gravity survey flown by SGL in 2012[2].
This tutorial should be run before running any of the other tutorials that utilise these data.
Intersection Analysis¶
An important analysis tool in airborne geophysics generally is intersection analysis which analyses the differences in some channel of data at the intersections of traverse and control flight-lines.
Repeat Lines¶
Another important analysis tool in airborne gravimetry in particular is repeat line analysis which analyses the repeatability in some channel of data over a series of flight-lines flown over the same planned line.
Odd - Even Grids¶
For surveys where the flight-lines are more closely spaced than the low-pass filter wavelength, odd-even grid analysis ([3]) is useful for assessing the noise in gravimeter data.
Gravimetry Corrections¶
There are four standard corrections that must be made to airborne gravity data: atmospheric correction, free-air correction, Eotvos correction and latitude correction. These corrections must be made using the modern standard formulae appropriate to airborne gravimetry. The formulae for the atmospheric, free-air and latitude corrections used here were taken from [4] where they appear in units of \(mGal\). Here they are modified to be in \(\mu ms^{-2}\) but galileoQC uses the units of the measured data, either \(mGal\) or \(\mu ms^{-2}\). The Eotvos correction formula was taken from [5] and also appears in [6].
Falcon Noise Analysis¶
The primary measure of noise in a Falcon survey is difference noise[7], and its relationship to turbulence. High frequency noise[8] is also a useful check for the QC of Falcon airborne survey data.
FTG Noise Analysis¶
The FTG is a single-complement, three-axis gradiometer. On each axis, it measures (\(\Gamma_{xy}^{i}\) and \(\Gamma_{uv}^{i}\)) relative to that (\(i\)-th) axis. Theoretically, the sum of the three \(\Gamma_{uv}^{i}\) should equal zero and variations from zero reflect error in the measurement. The actual quantity, called the in-line sum[9], must be scaled for the number of axes and is expressed as:
\[ \eta = \frac{\Gamma_{uv}^{1} + \Gamma_{uv}^{2} + \Gamma_{uv}^{3}}{\sqrt{3}} \]
The in-line sum tends generally to increase with turbulence so it is useful to plot it against turbulence.
In-line noise, and its relationship to turbulence, is the standard noise measure for FTG surveys.
There are mechanisms [8] by which gravity gradiometer noise at a frequency higher than the data frequency band can be down-converted to the data frequency band, resulting in errors in the data. This can occur in both AGG and FTG systems.
The checkHighFreq function checks for periods of high amplitude, high frequency signal in the raw gradiometer channels. It highlights sections of a survey line with excess high-frequency signal which might result in high gradient error. It is important to know that these erroneous gradients are true acceleration gradients and can be difficult to see by other methods.
Ground Gravity Comparisons¶
Airborne gravity test lines are flown to allow comparison with ground gravity. When making such comparisons, it is useful to know the sampling and quality of the ground gravity and, in Australia, this can be assessed by plotLinesOnGroundStns. This code relies heavily on the data collection[10] in its compiled form[11].
Statistical Analyses¶
Airborne survey data typically contain a large number of channels of data collected along a large number of flight-lines. It is useful, when reviewing any airborne geophysical survey, to be able to rapidly analyse and plot simple statistics so that any discrepancies or unusual behaviour can be rapidly found.
Grid Imaging¶
Most of the QC work is done on a line-by-line basis across the survey data. It is also useful to review images of the survey data interpolated to a regular grid because problems or artefacts in the data can be easier to see in an image. The following tutorial demonstrates some of the gridding and imaging functions.
Craig transform¶
The Craig transform method transforms differential curvature components \(G_{UV}\) and \(G_{NE}\) into vertical gravity[12]. This is useful because gravity interpreters are used to working with the gravity data, and because there are often regional or other gravity data that cover part or all of the survey area with which the transformed gravity data can be compared.
If regional gravity data are available, it is also possible to conform [13] the survey gravity, derived from the Craig transform , to the regional gravity.
The following tutorial demonstrates the use of the Craig transform and the conforming process.
Aeromagnetics¶
The following tutorial demonstrates some of the aeromag QC functions.
Data Acknowledgements¶
The tutorials use field data from airborne gravity surveys to demonstrate the use of galileoQC on real data. Permission to use field data has been kindly given by:
Stephan Sander (Co-President, Sander Geophysics),
Chris van Galder (Chief Geophysicist, Xcalibur Smart Mapping), and
Colm Murphy (Chief Geoscientist, Bell Geospace)
The Kauring AirGrav data were collected by Sander Geophysics in 2012 and are available, with report, at [2].
The Canobie Falcon field data were collected by Xcalibur Multiphysics in 2021. The final data and report are available at [14].
The Vinton Dome FTG final data were supplied by Bell Geospace. The data are described in [15].
The Eastern Victoria airborne gravimeter survey field data were supplied by Sander Geophysics in 2022-25. Details can be found at [16].