Hello Doug: Your question brings up a whole range of questions. Some of which are not possible to answer without more information.
Reduction to the Pole. Generally it is assumed that when one applies a RTP filter that the causative magnetisation is primarily induced. That is one should be using the Dec and Incl for the observation site for the correct time and year. When applied the resulting magnetic anomaly pattern should then be centred over the source body. The anomaly should be symmetric. If remanent magnetisation is present then as you state the effective, or total magnetic vector at the observation site is the vector summation of the induced and remanent components. Applying standard RTP filter as described on an effective vector above would result in a change in the distribution of anomaly pattern, BUT teh pattern would not be symmetrical over teh source body. Cordani has described a method where one uses a number of different dec and inc values at the source point to search for optimum "symmetry". Once the symmetry value is found then you have the direction of teh effective vector. You do not know the remanence vector since for that you would need to know the Koenigsberger ration (rem/induced). You do know that the remanenc direction does lie somewhere on the great circle connecting the PEF direction and your computed effective vector direction. Dealing with remanently magnetised sources is always a challenge. If you look at papers published by Clive Foss and colleagues in Australia you will find many suggestions. Simplest one is to transform your magnetic data into analytical signal and then to compute model on teh AS data. Recent versions of Geosoft's Voxi inversion software is designed to operate with remanently magnetised source bodies... this is the magnetic vector inversion procedure. I would start with Analytical Signal and then move to tmi and then to gradient data... using this progressive interpreatation protocol one can get structure and remanence information. And one last warning. If the rocks you are dealing with have been folded and the folding postdates acquisition of the remanence then you will have to have variable remanence correction. Best of luck. This is not easy stuff to deal with. Bill Morris On 10/24/2013 5:21 PM, Doug Perkin wrote: > Hi > I have a general question about the USGS Reduce to pole GXs. I always > use the simple reduce to pole calculation where you only need to > specify the geomagnetic inclination and declination. Has anyone used > the complete reduce to pole GX? This one also asks for the > magnetization inclination and declination, which I guess is the total > magnetization (remnant + induced). Which method is best for > estimating the average total magnetization inclination and declination? > Is this a good idea if you suspect strong remant magnetization? Or > should you just work with TMI and forget about RTP? > cheers, > Doug > > --- > > Forum archives can be accessed here: > http://lyris.geosoft.com/read/?fourm=geonet > > You are currently subscribed to geonet as: [email protected] > <mailto:[email protected]>. > > To subscribe or unsubscribe from any of our forums, select the User > Forum selection on the Geosoft Community page: > http://www.geosoft.com/support/community > -- Bill Morris Professor of Geography & Earth Sciences SGES, McMaster University Phone: 905-525-9140 x20116 --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?fourm=geonet You are currently subscribed to geonet as: [email protected]. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community
