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1.5 The effect of changing latitude on anomaly shapes in magnetic data

The sequence of images show the effect on anomaly shape of calculating the TMI for an East-West dyke and vertical cylinder, at different southern hemisphere latitudes. For latitudes between -30°S and -60°S the anomaly shapes are quite similar, with the main changes being the increasing anomaly amplitude with higher latitudes (because the Earth's field increases in intensity towards the poles). At latitudes near the pole and the equator the anomaly shape starts to become noticeably more symmetric, with highs over the bodies at the pole and lows over the bodies at the equator.

The cylindrical plug shows only orthogonal symmetry at the equator, whereas at the pole it shows radial symmetry.
Note how the offset of the magnetic high varies with latitude.

The grey scale images share a fixed look up table to illustrate the anomaly amplitude variations.
The colour images each have a look up table clipped to their maximum and minimum values to highlight the anomally shapes.

The plug is centred at 4800N 4000E and the dyke is centred on 2100N. The grid overlay has 1000 m spacing.
Click on the images to launch Noddy. A legend is provided at the end of this page.

	View of 500 m wide East-West dyke and 1000 m radius vertical cylindrical plug. LOAD JPEG IMAGE View direction is from SW.

	TMI at different latitudes with varying intensity of the Earth's magnetic field
Link	-0° eg Jakarta	-15° eg Singapore	-30° eg PNG	-45° eg Townsville	-60° eg Broken Hill	-75° eg South of Tasmania	-90° ie South Pole
Grey Scale	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Psuedo Colour	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Psuedo Colour Contours	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE	LOAD JPEG IMAGE
Earth's Field	25,000 gamma	35,000 gamma	44,000 gamma	50,000 gamma	56,000 gamma	64,000 gamma	70,000 gamma
Comment	Notice the orthogonal plug symmetry.						Notice the radial plug symmetry

Key	Survey Specifications	Scales
plug k = 10-2 dyke k = 10-2 background k = 0 image width 10,000 m	flying height 80 m	3000 -2000 max min

All models created using Noddy
Copyright © 1998-2002 AGCRC & Mark Jessell

WWW conversion by Ian Brayshaw