Reliability of CHAMP Anomaly Continuations

Abstract

Summary: CHAMP is recording state-of-the-art magnetic and gravity field observations at altitudes ranging over roughly 300 -550 km. However, anomaly continuation is severely limited by the non-uniqueness of the process and satellite anomaly errors. Indeed, our numerical anomaly simulations from satellite to airborne altitudes show that effective downward continuations of the CHAMP data are restricted to within approximately 50 km of the observation altitudes while upward continuations can be effective over a somewhat larger altitude range. The great unreliability of downward continuation requires that the satellite geopotential observations must be analyzed at satellite altitudes if the anomaly details are to be exploited most fully. Given current anomaly error levels, joint inversion of satellite and nearsurface anomalies is the best approach for implementing satellite geopotential observations for subsurface studies. We demonstrate the power of this approach using a crustal model constrained by joint inversions of near-surface and satellite magnetic and gravity observations for Maud Rise, Antarctica, in the southwestern Indian Ocean. Our modeling suggests that the dominant satellite altitude magnetic anomalies are produced by crustal thickness variations and remanent magnetization of the normal polarity Cretaceous Quiet Zone.

Spherical prism gravity effects by Gauss-Legendre quadrature integration

“…However, the anomaly relationships at different altitudes over the spherical patch study area are complicated by measurement errors and the non‐uniqueness of anomaly continuation (von Frese et al 2005). Sources with measurable effects at 20 km, for example, can have integrated effects at 250 km that are not measurable so that the effects observed at 250 km at best may only marginally constrain the field at 20 km.…”

“…However, the most reliable geological assessments of satellite gravity anomalies are made at the satellite altitudes of the observations because their analytical continuation to the surface is not unique and essentially dominated by dramatically amplified noise effects of measurement errors (e.g. von Frese et al 2005).…”

Gravity‐inferred crustal attributes of visible and buried impact basins on Mars

“…In contrast to previous MGS gravity studies that have considered the gravity predictions only at the Martian surface, we conduct our analysis at essentially satellite altitudes (i.e., 100 km) where the MGS gravity model predictions are much more strongly constrained by the gravity observations and the effects of local terrain density and elevation errors are greatly reduced [e.g., von Frese et al , 1999]. Furthermore, at satellite altitude we can analyze the MGS gravity anomalies at the effective resolution of the actual observations [e.g., Potts and von Frese , 2003a, 2003b; von Frese et al , 2004], while the poor reliability of conventional surface implementations of the MGS gravity anomaly estimates typically restricts analysis to the lower degree (≤60) components [e.g., Zuber et al , 2004].…”

Utility of Slepian basis functions for modeling near-surface and satellite magnetic anomalies of the Australian lithosphere

“…Satellite observations essentially recover longer-wavelength anomaly features, but not the higher-frequency anomalies near the Earth's surface due to the measurement errors (e.g., Kim et al 2004;von Frese et al 2005). Thus, the shorter-wavelength near-surface anomalies from terrestrial, shipborne, and airborne magnetic surveys provide important constraints to augment lithospheric studies of the satellite magnetic data.…”