Depth Module with FTMG
data products

The Depth Module includes our well tested AutoMag full survey processing system and our interactive QuickDepth, AI assisted anomaly focussed method. QuickDepth has the added bonus of generating full magnetic gradient tensor (FTMG) line data and grids along with a complete suite of FFT grid transformations.

Interactive and Process Oriented

AutoMag focuses on using all your line data for quality depth and dip estimation of semi-linear magnetic anomalies. QuickDepth works on individual anomalies along lines using AI to analyse the anomaly and help you select the best depth estimation method for the mapped anomaly shape.

The Depth Module utilises AI assisted depth interpretation:

Creates a full tensor magnetic gradient dataset (FTMG) from a TMI survey
Use the FTMG grids and other specialised grids for map interpretation
NSS, RTP, 1VD, Trend, Confidence,
Bxx, Byy, Bzz, Bxy, Bxz, Byz, Bx, By, Bz
AI assist uses the magnetic tensor for 3D shape detection
AI assist suggests the best estimation method
AI assist lets you know when an anomaly is unsuitable for depth estimation
FTMG line data provides maximum depth resolution
Compare results from the Tensor, Euler, Werner, Peters’ Length, and Tilt methods

For further details on the Depth Module refer to the Depth Module Technical Sheet.

QuickDepth

AI assisted anomaly depths

QuickDepth applies AI principles to the estimation of depth, magnetic properties and geological style from magnetic data. The AI speeds up the interpretation process but leaves the interpreter in control of the geological interpretation. It uses both the line data for the highest possible depth precision and the associated grids to gather intelligence on the shape characteristics of each anomaly.

QuickDepth is a new approach to calculating the depth to a magnetic source for isolated magnetic anomalies using a variety of interpretation techniques that do not require inversion. The method operates by dragging the mouse across the anomaly you want to interpret to produce immediate feedback on the depth to the source of the anomaly.

The input data is a high quality total magnetic intensity grid and the magnetic line data including the levelled magnetic field, sensor elevation and ground surface elevation or radar altimeter channels.

The magnetic tensor and a range of other magnetic measures are computed from the total magnetic field grid. This data provides key geological information that is used to assist in the depth interpretation and improve the quality of the estimates compared with conventional automated processes. Importantly, the depth is estimated from the data along the flight line to preserve the highest quality gradient information to produce the best possible depth estimates.

The tensor of the total magnetic field is used to derive geological characteristics such as strike direction, body type, centre of magnetization and depth to the top of the magnetic unit. This information is used to constrain and improve the precision of the other geophysical methods which include:

Euler 2D Method
Peters' Length Method
Tilt Depth Method
Euler 3D Method
Werner Deconvolution Method

We use the peak of the normalised source strength (NSS) from Clark (2014) to define the horizontal (X, Y) location of the centre of magnetisation which simplifies the calculations of depth for the Euler 2D, Werner and Tilt Depth methods. The strike direction of the anomaly (Pederson & Rasmussen, 1990) is used to correct the depth estimates for acute angle flight lines for the Tensor, Peters' Length, Werner Deconvolution and Tilt Depth methods.

The tensor analysis also provides a dimensionality index which automatically differentiates between pipe-link magnetic sources and linear magnetic formations or dykes. This allows for different depth correction techniques to be applied according to the geology. Some methods, such as Euler 2D analysis, are very sensitive to an incorrect choice of the geological magnetic source type. The tensor also provides some information about the width of the magnetic source and classifies it as thin, intermediate or thick.

Example images from the ModelVision magnetic depth interpretation tool QuickDepth

Importantly, the user is in control of the geology. While the underlying code does its best to determine the characteristics of the geological target, the automated selection can be overridden when appropriate.

The solutions can be exported as a point dataset to a Geosoft GDB database or CSV file for use in other applications. The data can be imported into ModelVision using the Convert Point to Body option for display of bodies in cross-section and map views.

For further reading on the principles of QuickDepth refer to the AEGC 2019 paper by David Pratt et al, titled, “An AI approach to using magnetic gradient tensor analysis for quick depth and property estimation”.

AutoMag

Turn line data into depth estimates

AutoMag is the best geologically focused automated magnetic depth interpretation system available with many productivity tools and cross-checks that enable you to interpret a full survey in a short period of time. An initial tuning phase is followed by multi-line processing and then interactive global filtering of the solutions to high grade the results by filtering low quality results and extreme attributes.

Smart Points and Depth Visualisation

This AutoMag example shows a map of Smart points representing strike and dip directions that are colour-coded by the processing level. Each level expands the depth of investigation search for multiple depth horizons. On completion of the processing, you can convert the Smart points to standard points for visualisation and analysis. Here the Symbols are shown as arrows with the estimated strike direction and colour code by depth below the ground surface.

AutoMag uses a grid trend analysis process to derive the magnetic trend azimuth and at the same time produces an estimate of the trend confidence. This value is highest for linear trends and lowest for noise or small circular features. We use the trend confidence to modify the size of the depth symbol to intuitively indicate the reliability of the depth estimate. In the example below, we exported the point data with all its attributes and applied a simple, second order weighted piecewise polynomial fit to the depths. We used AutoMag’s trend confidence as the weight to build a grid of the weighted depths that makes it easier to see the underlying depth trends. Contours of the weighted depth surface are shown as an overlay to the geology and AutoMag depth symbols.

Supervised Automation for Improved Quality and Efficiency

AutoMag bridges the gap between automated depth to magnetic source methods and pure interactive modelling and improves the quality and efficiency of depth to magnetic source calculations. It operates on a profile basis and is tightly integrated into the ModelVision modelling environment. Profiles can be analysed using original flight line data or traverses selected on gridded data. Large aeromagnetic surveys can be efficiently processed in batch mode using the recent addition of automated strike correction and dynamic filtering of solutions.

Based on a Refined Version of the Naudy Method

AutoMag is based on a refined version of the Naudy dipping tabular body inversion method which provides quality geological information for depth, magnetic susceptibility, thickness and dip. An innovative strike azimuth estimator has added the ability to automate corrections for geological units that cross the flight lines at an acute angle. This method out performs other automated methods because it uses a realistic geological model for steeply dipping, semi-linear magnetic rocks such as volcanics, ironstone formations and dykes.

Solutions produced by AutoMag can be converted directly into ModelVision 3D models, displayed as annotated symbols in map views or exported for use in other applications.

Depth Module with FTMG data products