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Session 10 - SOHO Helioseismology II, Interior.
Oral session, Saturday, June 28
Ballroom A, Chair: Thomas Bogdan

[10.03] Sensitivity of Time-Distance Helioseismology to Unwanted Instrumental and Solar Effects

J. Harvey, S. Jefferies (NSO/NOAO), T. L. Duvall Jr. (NASA/GSFC)

Correlation of the wave motions at one point on the surface of the sun with other points at different times and distances is the basis of time-distance helioseismology. This technique is especially promising for studies of local sub-surface structure and dynamics. Like any observational technique, the results depend on proper correction of instrumental effects and limitations, and also on an allowance for other signals and effects arising from the object that interfere with the desired signal. The former effects arise mainly from temporal and spatial sampling restrictions, data processing methods, geometrical distortion, and signal-to-noise limitations. The solar effects include the solar background noise, and surface and atmospheric excitation, propagation, and damping characteristics that tend to mask the small signals that represent internal conditions. In this study, we concentrate on instrumental effects. Based on data obtained at the geographic South Pole for 18 days in 1994, we find that time-distance correlations are not systematically affected by most instrumental characteristics with one exception. This exception is the spatial frequency response of the instrument. There is a substantial difference between correlations computed with and without allowance for spatial frequency response. This factor should be carefully considered when doing time-distance helioseismology analyses.

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