Magnetic Dipole Modelling Applet

Please read the description and instructions below before using the applet.

Objective, and additional details

• For an outline of the calculations have been set up for this applet, please see the mag.pdf page (Acrobat PDF format).
• Further discussion of magnetic units and how they are applied by this applet can be seen on the magunits.html page.
• A drag-and-drop quiz helps ensure you are aware of the sign convention for inclination and declination.

What is shown

• The colour map shows the strength of the chosen parameter (B_t, B_g, B_x, B_y, or B_z) as a function of position.
• Imagine doing a two dimensional survey over a susceptible sphere that has been magentized by the Earth's magnetic field specified by inclination and declination.  "Measurement" location is the centre of each coloured box. This is a simple (but easily programmable) alternative to generating a smooth contour map.
• The anomaly depends upon magnetic latitude, direction of the inducing (Earth's) field, the depth of the buried dipole, and the magnetic moment of the buried dipole.
• You can generate a profile along any line across the survey area by dragging the mouse in any direction over the top of the map. The amplitude scale is changed along with the colour map scale.
• Click on the anomaly profile to see the width of the anomaly at the point you have clicked. Anomaly width is noted on the graph by small blue marks on the axis, and a number (in metres).

Important Notes:

1. Inclination and declination describe the orientation of the Earth's ambient field at the centre of the survey area. Positive inclination implies you are in the northern hemisphere, and positive declination implies that magnetic north is to the east of geographic north.
2. The "length" adjuster changes the size of the square survey area. The default of 72 means the survey square is 72 metres on a side.
3. The "data spacing" adjuster changes the distance between measurements. The default of 4 means measurements were acquired over the survey square on a 4-metre grid. In other words, "data spacing = 4" means each coloured box is 4 m square.
4. The "depth" adjuster changes the depth (in metres) to the centre of the buried dipole.
5. The "magnetic moment" adjuster changes the strength of the induced field. Units are Am².  This is related to the strength of the inducing field, the susceptibility of the buried sphere, and the volume of susceptible material.
6. If you do not see a smooth 60 colour colourmap, click on the colourbar to use only 7 colours.
7. B_t, B_g, B_x, B_y, B_zare Total field, Gradient field, X-component (positive northwards), Y-component (positive eastwards), and Z-component (positive down) of the anomaly field respectively.
8. Clicking the Reset colours button changes the colour scale so that the end points of the colour scale are minimum and maximum values for the current data set.
9. Measurements are taken 1m above the surface.
10. For gradient data, measurements are taken at 1m and 2m.