Combining Satellite and Aeromagnetic Data Using Equivalent Source Technique

Abstract:

High-resolution aeromagnetic data have been collected for decades. These decades of magnetic survey data are merged to form province‐scale or even continental‐scale compilations (e.g., Australia). However, the long-wavelength part of the continental- scale compilation is often unreliable due to the procedures used in the survey data processing (leveling, reference field subtraction, diurnal variation correction) and the merging technique. It is difficult to assess the distorted part quantitatively although the wavelength could be up to distances comparable to the survey dimensions.

Satellite data might provide reliable long-wavelength components with a homogeneous global coverage and the use of satellite data to improve the long-wavelength components of near surface magnetic data is a common routine. The challenging task is to find the spectral ‘gap’ between satellite and aeromagnetic data. The conventional way of combining these two data sets is carried out by Fourier filtering. However, Fourier domain method suffers from spectral leakage and flat earth approximation problematic for continental-scale area.

Due to the limitations of the Fourier filtering method, we propose an equivalent dipole method to improve the long-wavelength part of the aeromagnetic data. First, physical parameters were derived from the magnetic data using equivalent source method. Then, physical parameters were converted to spherical harmonic coefficients in regional area. Consequently, the classical spherical harmonic analysis can be applied to validate the spectral consistency of the two data sets.

We tested our approach on a high quality, large-scale magnetic compilation of Australia. To investigate the efficiency of our proposed method, we used the LCS-1 satellite model and World Digital Magnetic Anomaly Map for comparison.