Hi everyone, and special thanx to Ken for all the Calgary Meeting updates. While SEG-members will be busy giving each other esteemed awards, Crebs will hopefully be discovering orebodies <grin>; to that: Interpretation geophysicists should be aware that Fugro's helicopter electromagnetic (HEM) systems now normalize the coplanar-coil signal response DIFFERENTLY than the Dighem systems prior to 1999. The new normalization process essentially doubles the response magnitude (in units of ppm); and apparently is normalized similar to the previous High-Sense, Aerodat, and SIAL HEM-systems. The coaxial-coil normalization remains the same as earlier pre-1999 systems. This is very important to interpretation geophysicists who rely on coaxial-to-coplanar (@ "nearby" frequencies) response-ratios to help discriminate conductive ore-geometries from culture and graphitic conductors. Whereas spherical-shaped ore-geometries prior to 1999 yielded a Dighem theoretical-ratio of 1/4 ; the new Fugro coplanar normalization yields a ratio of 1/8! (Here's a real example, the Voisey's Bay "Ovoid" orebody yielded a coaxial-to-coplanar ratio of about 2/7 (@ near 900-hertz) when surveyed by Dighem for me in 1995; therefore, under the new Fugro normalization its ratio would be 1/7.) This could also be important when comparing older Dighem surveys with newer Fugro-acquired data. If you use older Dighem characteristic curves for profile interpretations, make a note of the change. Processing geophysicists should also be aware of this normalization change; so fix your filtering/modeling/inversion algorithms accordingly. Good Prospecting, Terry J. Crebs formerly, Chief Geophysicist, Diamond Fields Resources, Inc. Lakewood, CO USA http://www.crebs.com _______________________________________________________ List archive: http://www.mail-archive.com/[email protected]
