New multi-taper spectral analysis of GONG data
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Multi-taper spectral analysis significantly increases the number of frequency measurements that GONG is able to extract from its data. Seen here are the results for a typical 108-day time series (GONG Months 58-60), with the traditional approach on the left and the multi-taper results on the right. Dots indicate multiplets where some modes were fitted, while crosses indicate that the mode coverage was high enough to fit the multiplet. The colors indicate the fraction of all (2+1) modes per multiplet that are fitted, and the thick solid line indicates the boundary of the region where leakage makes fitting difficult. The multi-taper method leads to more modes and multiplets at low frequencies and at low values. Overall, the number of good fits increases by about 28 percent, and the number of multiplets increases by about 14 percent, while introducing no bias in the frequencies. See the GONG update report in the December 2001 NOAO Newsletter (currently only available in PDF format).
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