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The effect of spacecraft radiation sources on electron moments from the Cassini CAPS electron spectrometer

Arridge, Chris S. and Gilbert, Linda K. and Lewis, Gethyn R. and Sittler, E.C. and Jones, Geraint H. and Kataria, D.O. and Coates, Andrew J. and Young, D.T. (2009) The effect of spacecraft radiation sources on electron moments from the Cassini CAPS electron spectrometer. Planetary and Space Science 57 (7), pp. 854-869. ISSN 0032-0633.

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Data from the Cassini plasma spectrometer (CAPS) electron spectrometer (ELS) have been found to be contaminated with an energy-independent background count rate which has been associated with radiation sources on Cassini. In this paper we describe this background radiation and quantitatively assess its impact on numerically integrated electron moments. The general properties of such a background and its effects on numerical moments are derived. The properties of the ELS background are described and a model for the background presented. A model to generate synthetic ELS spectra is presented and used to evaluate the density and temperature of pure noise and then extended to include ambient distributions. It is shown that the presence of noise produces a saturation of the electron density and temperature at quasi-constant values when the instrument is at background, but that these noise level moments are dependent on the floating spacecraft potential and the orientation of the ELS instrument with respect to the spacecraft. When the ambient distribution has a poor signal-to-noise ratio (SNR) the noise determines the density and temperature; however, as the SNR increases (increasing primarily with density) the density and temperature tend to those of the ambient distribution. It is also shown that these noise effects produce highly artificial density–temperature inverse correlations. A method to subtract this noise is presented and shown to correct for the presence of the noise. Simulated error estimates for the density and temperature are also presented. The analysis described in this paper not only applies to weak background noise, but also to more significant penetrating backgrounds such as those in radiation belt regions of planetary magnetospheres.

Item Type: Article
Keyword(s) / Subject(s): Cassini, electrostatic analyser, penetrating radiation, moments, noise subtraction
School or Research Centre: Birkbeck Schools and Research Centres > School of Science > Earth and Planetary Sciences > UCL/Birkbeck Centre for Planetary Sciences
Depositing User: Administrator
Date Deposited: 28 Jul 2011 08:39
Last Modified: 17 Apr 2013 12:21

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