Identification and removal of flight system-generated AC fields
Abstract
Definitive detection of the remanent magnetic field of small bodies in our solar system such as asteroids, comets and small moons have been elusive. For example, past missions have determined only the upper limit on the magnetization of objects like (21) Lutetia and (433) Eros, (9969) Braille and other asteroids. Given the typical sub-nT sensitivity of modern magnetometers, the main noise source for most spacecraft magnetometry investigations are stray fields from the flight system. Techniques for removing the flight system-generated AC signatures typically involve band-pass, low-pass or notch filtering the measurements based on ancillary and housekeeping data. A key limitation of this approach is that filters remove all of the fluctuations in a given range including those associated with the ambient field that is the target of the science investigation. Peak suppression is an alternative signal processing technique in which fluctuations at specific frequencies are removed from a data set. The main difference between peak suppression and a notch filter is that you select specific frequencies and set their power to zero rather than selecting a frequency band to attenuate. Peak suppression can be used to remove dominant spectral peaks in order to study smaller fluctuations or to remove smaller scale fluctuations in order to retrieve a clean measurement. For example, in nuclear magnetic resonance spectroscopy, peak suppression is used to remove the known emissions from dominant molecules, such as oxygen, in order to study the behavior of trace elements (Antoine et al. 2000). We demonstrate that, for magnetic field investigations that include two or more instruments in a gradiometer configuration, peak suppression is a viable method for removing flight system-generated AC fields from magnetic field measurements. The dominant frequencies in the flight system field can be identified using the spectral content of $\Delta$B=B$ _{in$}-B$ _{out$} and peak suppression can be used to set the power at those frequencies to zero in the spectra of the observed field. In particular, this method can be used to identify and remove flight system-generated fluctuations without affecting the ambient field anytime the flight system and ambient field frequencies differ by more the 0.1 Hz. Reference: Antoine, J.-P., Coron, A., & Dereppe, J.-M. (2000). Water peak suppression: Time-frequency vs time-scale approach. Journal of Magnetic Resonance, 144(2), 189 -194. Retrieved from http://www.sciencedirect.com/science/article/pii/S1090780799920116 doi: https://doi.org/10.1006/jmre.1999.2011
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.304R