Magnetic Anomalies: Anywhere and Anytime – Accurate Information for Use in Alternative Navigation

Alternative navigation (AltNav) includes development of magnetic navigation (MagNav) using the Earth’s magnetic field as a reference. Current implementation requires highly accurate estimates of the full expected magnetic field along the predicted travel path. This is a challenging problem.

This presentation focuses on delivery of trustable estimates of the crustal magnetic anomaly as a component of the full field. In many operational situations (depending on altitude and speed), the variations of the crustal magnetic field represent the primary signal for use in MagNav.

One key challenge is the integration of original survey data into a comprehensive grid/model with accompanying estimation of the anomaly uncertainty. The required resolution and accuracy of this information will vary depending on navigational operation, but current MagNav implementations are dependent on highly accurate anomaly estimation. To meet this requirement, it is important to assess and optimize: (1) the quality and sampling of the original survey data; (2) the methods used to interpolate the survey data into a regular grid; and (3) the upward (or downward) continuation of the data (both for anomaly and directional gradient) to the required navigational position.

We report on methods developed for these 3 requirements using (1) FFT-based power spectrum analysis of initial survey sampling, (2) a new method for magnetic grid cell uncertainty estimation, and (3) experimentation with generalized equivalent source techniques for on-the-fly calculation of anomaly and directional gradient at selected locations.