Title: Spectral Estimation of Plasma Fluctuations I: Comparison of Methods,
Abstract: The relative root mean squared errors (RMSE) of nonparametric methods for
spectral estimation is compared for microwave scattering data of plasma
fluctuations. These methods reduce the variance of the periodogram estimate by
averaging the spectrum over a frequency bandwidth. As the bandwidth increases,
the variance decreases, but the bias error increases. The plasma spectra vary
by over four orders of magnitude, and therefore, using a spectral window is
necessary. We compare the smoothed tapered periodogram with the adaptive
multiple taper methods and hybrid methods. We find that a hybrid method, which
uses four orthogonal tapers and then applies a kernel smoother, performs best.
For 300 point data segments, even an optimized smoothed tapered periodogram has
a 24 \% larger relative RMSE than the hybrid method. We present two new
adaptive multi-taper weightings which outperform Thomson's original adaptive
weighting.