(color online) (a) The amplitude of the fundamental frequency component of the gravitational background signal in small parts versus time, and (b) the amplitude of second harmonic components of the in small parts versus time. Each blue point denotes the obtained amplitude with the cosine oscillation influence corrected in a small part by the improved correlation method, and each black point denotes the obtained amplitude without correcting the cosine oscillation influence in a small part in the same way. The asterisks and their error bars denote the final values and uncertainties of the amplitudes. Some blue points overlap with corresponding black points, since their differences are too small to distinguish.