Hello, Thanks for the suggestions. Best regards, Ana De: Gerry Connard <[email protected]> [mailto:[email protected]] Enviada: segunda-feira, 23 de Novembro de 2015 18:44 Para: Geosoft Oasis montaj and Target Assunto: RE: [geonet] Potential field data modeling in GM-SYS
As Ed points out, using RTP where remanence is present can cause problems. In general it is better to use TMI data. GM-SYS does not apply a correction to the TMI data but uses the external field parameters to calculate the model response in the presence of that external field. The only exception to this recommendation is the case where the external field varies significantly over your model (for example a long profile near the magnetic pole). In this case you may be better off doing a variable RTP before trying to model because GM-SYS only allows you to enter 1 definition for the external field. Most modern aeromag surveys remove the variations in the IGRF/DGRF from the final delivered data. They typically subtract the appropriate field based on the location & elevation of each measured point. Alternatively, the contractors compute a grid of IGRF values across the survey area and subtract that from the observed data. The ‘total field” magnetic anomaly is a scalar value derived by taking the dot product of the observed vector magnetic field with the regional field (i.e. the IGRF) at that point. See Blakely (1995, p178-179). GM-SYS 2D and 3D need the regional field strength value and direction to calculate the total field anomaly. Blakely, R.J., 1995, Potential Theory in Gravity & Magnetic Applications: Cambridge University Press, pp.441. Gerry From: edcunion <[email protected]<mailto:[email protected]>> [mailto:[email protected]] Sent: Monday, November 23, 2015 9:19 AM To: Geosoft Oasis montaj and Target Subject: Re: [geonet] Potential field data modeling in GM-SYS On your latter general remanence query, the RTP filtered product can show affects when remanence is present, the affects can be exacerbated at low magnetic latitudes. Comparing the TMI and RTP with the analytic signal or its individual derivative components (dX, dY, dZ) for your data can add some insight. The ASVI (analytic signal of the vertical integral, in Macleod et al 1993) can also be tried and compared, the reference is quoted below and outlines this method- "Macleod, I.N., Vieira, S., Chaves, A.C., 1993; Analytic signal and reduction to the pole in the interpretation of total magnetic field data at low magnetic latitudes, Proceedings of the third international congress of the Brazilian Society of Geophysicists." Ed On Monday, November 23, 2015 9:17 AM, author.nameemail <[email protected]<mailto:[email protected]>> wrote: Hello, I want to clarify some doubts about potential field data modeling in GM-SYS. I can use the TMI or the RTP anomaly when I am modeling magnetic data. But when I am modeling simultaneously magnetic and gravity data is better to use the gravity and reduced to the pole magnetic anomaly? Because the dipolar effect is removed and magnetic anomalies are transformed to monopolar like the gravity anomaly. Ideally what anomaly should I use in this case? Or does the GMSYS apply some correction to the TMI data, because when I create a gmsys model I have to define the magnetic field parameters (magnitude, inclination and declination) at the measurement location? Other question is related to the presence of remanance magnetization. When remanent magnetization is present is better to use the TMI data and not the RTP anomaly? Or I can use other derivative grid like the analytical signal? Best regards, Ana --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet<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/forums/register/ --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet<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/forums/register/ --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet<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/forums/register/ --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=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/forums/register/
