Inversion of Airborne Electromagnetic Survey Data, Styx River Area, Alaska

Abstract:

A joint effort by the US Geological Survey (USGS) and the Alaska Division of Geological & Geophysical Surveys (DGGS) aims to add value to public domain airborne electromagnetic (AEM) data, collected in Alaska, through the application of newly developed advanced inversion methods to produce resistivity depth sections along flight lines. Derivative products are new geophysical data maps, interpretative profiles and displays. An important task of the new processing is to facilitate calibration or leveling between adjacent surveys flown with different systems in different years. The new approach will facilitate integration of the geophysical data in the interpretation and construction of geologic framework, resource evaluations and to geotechnical studies.

Four helicopter airborne electromagnetic (AEM) surveys have been flown in the Styx River area by the DGGS; Styx River, Middle Styx, East Styx, and Farewell. The Styx River flown in 2008 and Middle Styx in flown 2013, cover an area of 2300 square kilometers. These data consist of frequency-domain DIGHEM V surveys which have been numerically processed and interpreted to yield a three-dimensional model of electrical resistivity. We describe the numerical interpretation methodology (inversion) in detail, from quality assessment to interpretation. We show two methods of inversion used in these datasets, deterministic and stochastic, and describe how we use these results to define calibration parameters and assess the quality of the datasets. We also describe the difficulties and procedures for combining datasets acquired at different times.