Thanks Elizabeth, Jean From: [email protected] To: [email protected] Subject: RE: [geonet] Susceptibility unit Date: Mon, 16 Jun 2014 18:11:48 +0000
Hello Jean Thank you for bringing the susceptibility unit discrepancy forward along with a descriptive illustration. The delay in responding is due to the fact that we checked the code and indeed the units are SI (not e.m.u). The help content is being corrected to indicated SI units. You will see the correction in the next Oasis montaj update. Elizabeth Baranyi Technical Product Manager, Geophysical GEOSOFT INC. freedom to explore T +1 416.369.0111 #356 C +1 647.504.6006 F +1 416.369.9599 Visit our site at www.geosoft.com -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of JeanH Sent: Thursday, June 12, 2014 2:27 PM To: Geosoft Oasis montaj and Target Subject: [geonet] Susceptibility unit I calculated the susceptibility with 1D-FFT. In FFTUSC GX help, it is noted: "The susceptibility filter calculates the apparent magnetic susceptibility of the magnetic sources using the following assumptions: • The magnetic field has had the IGRF removed. • There is no remnant magnetization. • All magnetic response is caused by a collection of vertical prisms of infinite depth extent. • The result is in unit of e.m.u. So, I used the residual : Total field- IGRF. Resulting susceptibilitity values ranges from -0.042 and 0.081 with a mean of -0.000 and a stadard deviation of 0.002 And I calculated the susceptibility with MagMap. In FFT2CON SUSC help, it is noted: "The susceptibility filter operator calculates the apparent magnetic susceptibility of the magnetic sources using the following assumptions: • The IGRF has been subtracted from the input magnetic field prior to filtering. • There is no remanent magnetization. • All magnetic response is caused by a collection of vertical, square-ended prisms of infinite depth extent. • The resulting susceptibility data is in SI units. I gridded the Residual and I calculated the susceptibility grid with Magmap. Susceptibility stats for the grid are : Min: -0.0133 Max: 0.0363 Mean: -0.0004 SD: 0.0012 I sampled the grid to the database. Sampled susceptibility values are between -0.008 and 0.0232 with a mean of -0.0004 and SD of 0.0011. I calculated the ratio Susc_2Dfft/Susc_1Dfft and the mean is 1.26 If Magmap give the susceptibility in SI and 1DFFt in e.m.u., the mean of the ratios should be around 4* PI or 12.6664. If, in the database, I do the profile of both susceptibilities with the same scale, they almost coincide, but the profile of the convert 1D-FFT susceptibilities in SI goes off-scale. So there is probably an error in the help file. Both Magmap and 1D-FFT give the susceptibility in the same unit, but which one? emu or SI? In the figure, green is Susc_1D-FFT(emu), gray is Susc_2D-FFT(SI) and red Susc_1D_FFT*4*PI (SI). --- 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 --- 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 --- 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
