Abstract
Gaussian phase-speed filters are widely used in time-distance helioseismology to select specific wave packets whose travel times are then measured at the solar surface. This filtering increases the signal-to-noise (S/N) ratio of the temporal cross-covariances that are fitted to derive the travel times. The central phase speeds of these Gaussian filters are prescribed by a solar model; their widths are typically chosen empirically. No systematic study has been published on the effect of this filter width on the S/N ratio of the travel times. Such an analysis requires the ability to generate both noise and signal travel-time perturbations, this is now possible due to the recent introduction of a noise model and Born-approximation sensitivity kernels. These kernels allow for a derivation of travel-time perturbations as functions of a given sound-speed perturbation and are dependent on the phase-speed filters applied to the data, unlike simpler kernels. In this paper, we show that there is indeed an optimum value of the filter width that results in a maximum S/N ratio for the travel-time maps. Narrower filters exclude too much signal to produce useful travel-time perturbation maps, while broader filters are not selective enough.
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Birch, A.C., Kosovichev, A.G., Price, G.H., and Schlottmann, R.B.: 2001, Astrophys. J. 561, L229.
Birch, A.C., Kosovichev, A.G., and Duvall, T.L. Jr.: 2004, Astrophys. J. 608, 580.
Braun, D.C., Duvall, T.L. Jr., and LaBonte, B.L.: 1987, Astrophys. J. 319, L27.
Couvidat, S., Gizon, L., Birch, A.C., Larsen, R.M., and Kosovichev, A.G.: 2005, Astrophys. J. Suppl. 158, 217.
Couvidat, S., Birch, A.C., and Kosovichev, A.G.: 2006, Astrophys. J. 640, 516.
Duvall, T.L. Jr., Jefferies, S.M., Harvey, J.W., and Pomerantz, M.A.: 1993, Nature 362, 430.
Duvall, T.L. Jr., et al.: 1997, Solar Phys. 170, 63.
Gizon, L. and Birch, A.C.: 2002, Astrophys. J. 571, 966.
Gizon, L. and Birch, A.C.: 2004, Astrophys. J. 614, 472.
Jensen, J.M.: 2001, Ph.D. thesis, University of Aarhus, Denmark.
Jensen, J.M., Duvall, T.L. Jr., and Jacobsen, B.H.: 2003, in H. Lacoste (ed.), Proceedings of the SoHO 12/GONG+ 2002 Workshop, ESA publications SP-517, ESA Publications Division, Noordwijk, Netherlands, p. 315.
Kosovichev, A.G. and Duvall, T.L. Jr.: 1997, in F.P. Pijpers, J. Christensen-Dalsgaard, and C.S. (eds.), Proceedings of SCORe’96: Solar Convection and Oscillations and Their, Aarhus, Denmark, Astrophysics and Space Science Library, Kluwer Academic, Vol. 225, p. 241.
Kosovichev, A.G., Duvall, T.L. Jr., and Scherrer, P.H.: 2000, Solar Phys. 192, 159.
Rajaguru, S.P., Hughes, S.J., and Thompson, M.J.: 2004, Solar Phys. 220, 381.
Scherrer, P.H., et al.: 1995, Solar Phys. 162, 129.
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Couvidat, S., Birch, A.C. Optimal Gaussian Phase-Speed Filters in Time-Distance Helioseismology. Sol Phys 237, 229–243 (2006). https://doi.org/10.1007/s11207-006-0209-z
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DOI: https://doi.org/10.1007/s11207-006-0209-z