Hello everybody,
I was wondering which method is better when processing a residual magnetic field over an underground buried body, is that to do the RTP reduction to pole at first , then calculating the depth to the center or top of the body by using the x1/2 method? .Or calculating depth from the dipolar anomaly of the body by using Peters method before reducing to pole?
Regards.
I think is better to first reduce the magnetic anomaly to pole then calculating the depth.
The RTP map show the correct situation of a anomaly source. Also, after reduction to pole is change the form of the magnetic field map (in most areas) , thus deep estimated will be different, specific in resulted solutions from Euler method.
Ata
In my opinion, it is better to avoid RTP transform for depth estimation. In RTP transformation, it is assumed that the overall magnetic vector is parallel with the undisturbed geomagnetic field. However, in an anomalous zone, the mentioned vector can be very different due to remanent magnetization especially for very intensive anomalies (e.g. magnetite ore bodies). This effect could be more severe on manual or semi-manual depth estimation results. Furthermore, in areas with great variations of inclination and declination, it must be avoided because it is contaminated by great errors.
There are a lot of methods for magnetic anomaly depth estimation:
1. Euler deconvolution (if you want to apply it, you MUST read at least three papers on that, those written by "Reid" and others. Just search you can find them (i think that the years of publication was 1990, 2014,2015).
2. Half-slope
3. Estimating by using Tilt derivative
4. Amplitude method
5. Parasnis method
6. An-Eul method (uses euler basic technique)
7. Bot & Smith method
8. Werner Deconvolution
....
There are many methods, but i have not seen or experienced which one is better.
I have compared the mentioned methods (except werner and amplitude) in a case study in my BSc thesis. I am not certain of the results because it was just one case study. The results are as follows:
In my small test, the Euler is better to be used just in regional recognaissance surveys. I have seen a lot of cases in the iranian mineral exploration programs using this incorrectly in small surveys. The other methods was almost scattered within 20-30% of the average estimated depth. The great differences might be OK since the accuracy of magnetic depth is too lower than electrics or seismics.
Hope this notes could help you.
Regards
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