Magnetic gradiometry using frequency-domain filtering

Abstract

Accurate measurements of ambient planetary and interplanetary magnetic fields using spacecraft magnetometers typically require accounting for interfering magnetic fields generated by the flight system (FS). The most common method for removing FS-generated time-variable magnetic fields is narrow-band and low-pass filtering of magnetic field data in the frequency domain. However, if fluctuations in the ambient field contain frequencies overlapping those in the FS field, it can be difficult to construct a filter that will not affect both signals. Here we present an alternate method for removing FS time-variable signatures from magnetic field measurements. For spacecraft that make use of a magnetic gradiometer (i.e. with two or more instruments on a boom at different distances from the center of the spacecraft), the dominant frequencies in the FS field can be identified using spectra of the differenced field components. The amplitudes of the FS field at those frequencies can then be suppressed without removing spectral peaks present in the ambient field. We demonstrate the successful application of this method, referred to as gradiometry peak suppression, both to modeled data sets and to 128 Hz Venus Express magnetometer data.

The Psyche Magnetometry Investigation

“…First, measurements from both SUs will enable gradiometry methods in which the flight system field can be characterized based on its property of being stronger in intensity at the inboard relative to the outboard sensor (Ream et al. 2021 ). Second, monitoring variations of the solar wind (Leinweber et al.…”

“…Estimated flight system >0.1 Hz fields will be identified and removed using frequency-domain filtering of gradiometry measurements (Ream et al. 2021 ). In particular, intervals containing flight system >0.1 Hz fields can be identified when a simultaneous change occurs in the rolling maximum and minimum (upper and lower envelope) of the differenced field, .…”

“…These contributions can then be suppressed by reducing the power in the identified frequencies to the noise level (Ream et al. 2021 ). Because the differenced field does not contain ambient field fluctuations, this filtering will not affect the spectral peaks of the time-variable ambient fields.…”

Separation of Spacecraft Noise From Geomagnetic Field Observations Through Density‐Based Cluster Analysis and Compressive Sensing

“…Ream et al. (2021) uses gradients in the frequency domain to identify and suppress spacecraft noise. However, this method assumes that the spectra of the ambient magnetic field and the spacecraft noise do not overlap.…”

“…This method can also be applied to higher order magnetic fields but requires arduous pre-flight characterization of the spacecraft's magnetic signature. Ream et al (2021) uses gradients in the frequency domain to identify and suppress spacecraft noise. However, this method assumes that the spectra of the ambient magnetic field and the spacecraft noise do not overlap.…”