Thanks. Looks like a good workaround. But one more thing to remember :-) Best, -tiku
On Dec 4, 2015, at 3:21 AM, lucaingv <[email protected]> wrote: > Hi Tiku, > I know very well the issue you raised but I solved it bypassing the initial > configuration. Once you try to create a new model GMSYS program requires the > values of the Earth's field in A/m. In order to obtain the parameter in nT > (which is the unit of measure that gives us the IGRF) you have to do as > follows: > in the display menu, you select as anomaly units cgs > after that, in the profile menu click the "set Earth's field parameters" and > at this time the related popup menu is finally in nT. > If you need to work with susceptibility values in A/m unit don't forget to > change the anomaly units another time. > So in this way you can put the IGRF value and start with your modeling. > I hope that this can help you > All the Best > Luca > > > > > Il giorno 03/dic/2015, alle ore 22:58, Dhananjay Ravat ha scritto: > >> On an unrelated topic, I noticed the following labeling problem today in one >> of the GM-SYS input boxes when I was showing some students in my class the >> basic model construction in GM-SYS. I believe I am using OM 8.1 or 8.2. The >> box where one inputs the earth’s magnetic field parameter, the unit for the >> field intensity is labeled as A/m. It should be nT because when one >> actually converts nT or Orsted into A/m the value is not consistent with >> what the program expects (it expects nT, e.g. 50000 nT, and not 0.5 Oe / >> (4pi x 10^-3) which would be in A/m). When IGRF calculator pulls in these >> values, it pulls in nT (but the label for the unit is still A/m I think). >> Hadn’t used GM-SYS in a while and so not noticed this before. >> >> I was wondering why my model was not producing any anomaly at all…. Anyway, >> magnetic units are already confusing to most and so if this is not already >> corrected in the later versions, it should be corrected. I.e., the label >> A/m for earth’s field intensity should be changed to nT. >> >> Best, >> >> tiku >> _____________________________ >> D. Ravat | Professor of Geophysics >> Earth & Environmental Sciences | Physics & Astronomy >> University of Kentucky >> 101 Slone Research Building | Lexington, KY 40506-0053 >> fax: +1 859 323 1938 >> >> Web: >> http://ees.as.uky.edu/users/drava2 >> https://www.researchgate.net/profile/Dhananjay_Ravat/ >> https://ees.as.uky.edu/gravity-magnetics-heat-flow-tectonics >> https://ees.as.uky.edu/near-surface-geophysics >> _____________________________ >> >> >> >> >> >> >> On Nov 23, 2015, at 1:44 PM, Gerry Connard <[email protected]> wrote: >> >>> 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]] >>> 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]> 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 >>> 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/ >>> >>> --- >>> >>> 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/ >>> >>> --- >>> >>> 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/ >>> >> >> --- >> >> 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/ >> > >>> ----- >>> >>> Luca Cocchi >>> >>> Istituto Nazionale di Geofisica e Vulcanologia, >>> Unità di Progetto "Geofisica e Tecnologie Marine" >>> >>> Villa Pezzino >>> >>> Via Pezzino Basso, 2 >>> >>> 19025 La Spezia >>> >>> Tel 0187794408 >>> fax 0187766400 >>> [email protected] > >> > > > --- > > 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/ > --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet You are currently subscribed to geonet as: [email protected]. 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