rms and covariance spectra of U1-U3 (left panels) and O1-O2 (right panels). Blue curve is the best-fit model to the covariance spectrum. rms and covariance spectra of O1-O2 are also overplotted on those of observations U1-U3 (left panel, grey squares) for an easier comparison. The bottom panels show the ratio of rms and covariance spectra to the best-fit model of the covariance spectrum.