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SEPARATION OF SPIN SYNCHRONIZED SIGNALS

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T. HIGUCHI, G. K. CRAWFORD, R. J. STRANGEWAY AND C. T. RUSSELL

*Institute of Geophysics and Planetary Physics, University of California,*

Los Angeles, CA 90024-1567, U.S.A.
(Received March 16, 1992; revised November 17, 1993)

**Abstract.**
In the measurements of VLF electric fields with the
Pioneer
Venus spacecraft in sunlight, spin synchronized signals often dominate over the
naturally generated emissions. We present a method to separate natural emissions
from the several possible sources of noise. Our major objective by this
method is
not to remove all spin modulation, but to effectively subtract the
background noise
caused by the identifiable noise sources. Examination of the data shows that the
background spin synchronized noise is quite sensitive to *theta*(*n*), the angle
between the sense axis and the solar direction. We model the observed data as
*y*(*n*) = *w*(*n*)*t*(*n*)*f*(*theta*(*n*)) + *x*(*n*), where *f*(*theta*) represents the phase
response
of the background noise and *x*(*n*) is the estimated natural emissions.
*t*(*n*) and
(*n*) are the long-term trend component and time- and phase-independent
component
of the intensity of the background noise, respectively. The method to decompose
*y*(*n*) is based on the Bayesian approach which has been recently applied to
various
inversion problems such as nonstationary time series modeling and image
reconstruction. In this procedure, the estimated parameters *w*(*n*), *t*(*n*),
*f*(*theta*), and *x*(*n*) can be determined automatically. We will describe the
Bayesian scheme and its application to the Pioneer Venus VLF electric field
data.

*Key words and phrases*:
Time series, Bayesian
approach, outlier detection, smoothing, nonlinear
modeling.

**Source**
( TeX ,
DVI ,
PS )