SEPARATION OF SPIN SYNCHRONIZED SIGNALS

In the measurements of VLF electric fields with the Pioneer Venus spac ecraft 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 objec tive by this method is not to remove all spin modulation, but to effec tively subtract the background noise caused by the identifiable noise sources. Examination of the data shows that the background spin synchr onized noise is quite sensitive to theta(n), the angle between the sen se 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 respon se of the background noise and x(n) is the estimated natural emissions . t(n) and w(n) are the long-term trend component and time- and phase- independent component of the intensity of the background noise, respec tively. 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.