Recent advances in the verification and geologic interpretation of satellite‐altitude magnetic anomalies

Application of satellite magnetic observations for estimating near-surface magnetic anomalies

“…The term "joint inversion" in geophysics refers to the inversions of independently observed data sets (e.g., Ravat et al, 1998Ravat et al, , 2002Li and Oldenburg, 1990;von Frese et al, 1999a). For this application, the design matrix is given by A = [A aero A sat ] T , where A aero and A sat are submatrics of respective orders (n aero × m) and (n sat × m) that reflect the geometric relationships between the crustal prism source coordinates and the respective aeromagnetic and satellite observation coordinates.…”

“…Local representations from equivalent source models (e.g., Dampney, 1969;Mayhew, 1982;von Frese et al, 1981b;Purucker et al, 1996;) can more fully account for the local data qualities and errors in the magnetic observations. Excepting the long wavelength magnetic anomalies over Canada (Arkani-Hamed et al, 1995;Pilkington and Roest, 1996;Ravat et al, 2002), however, comparisons of downward continued satellite magnetic anomalies with nearsurface survey data, or upward continued near-surface survey anomalies with satellite anomalies have mostly yielded poorly correlated and inconsistent results (e.g., von Frese et al, 1982;Sexton et al, 1982;Schnetzler et al, 1985;Grauch, 1993;Whaler, 1994;Ravat et al, 1998). Figure 1 shows an example of the inconsistencies of continuing individual anomaly fields over great altitude differences.…”

“…Hence, in the absence of measurements in the intervening altitudes to constrain the nonunique continuation estimates, there seems to be little recourse but to consider the continuations of these anomalies in the context of anomaly models that jointly satisfy both the satellite and near-surface measurements. This joint inversion approach was initially implemented over Canada by weighting the satellite and aeromagnetic anomalies to adjust the inversion for the different survey error levels (Ravat et al, 1998(Ravat et al, , 2002. However, simple unweighted inversions of near-surface and satellite magnetic anomalies have also yielded geologically plausible results, such as for the Weddell Sea region of Antarctica where magnetic anomaly error levels were poorly constrained at all altitudes (von Frese et al, 1999a).…”

Crustal analysis of maud rise from combined satellite and near-surface magnetic survey data

“…We fit these anomalies to an array of crustal dipoles using least squares matrix inversion to solve for the magnetizations of the dipoles (von Frese et al, 1981a;von Frese, 1998). We then evaluated our point dipole model at 700 km for anomaly estimates over the Agulhas Plateau region to compare with our Ørsted anomalies over the Maud Rise region.…”

“…Specifically, we determined another set of volume magnetic susceptibilities for the crustal prisms in Fig. 2(D) from the joint inversion (Ravat et al, 1998) of these ADMAP near-surface residuals and the Ørsted residuals in Fig. 4(B).…”