Comparison of Travel-Time and Amplitude Measurements for Deep-Focusing Time--Distance Helioseismology
arXiv:1804.02311 · doi:10.1007/s11207-018-1283-8
Abstract
The purpose of deep-focusing time--distance helioseismology is to construct seismic measurements that have a high sensitivity to the physical conditions at a desired target point in the solar interior. With this technique, pairs of points on the solar surface are chosen such that acoustic ray paths intersect at this target (focus) point. Considering acoustic waves in a homogeneous medium, we compare travel-time and amplitude measurements extracted from the deep-focusing cross-covariance functions. Using a single-scattering approximation, we find that the spatial sensitivity of deep-focusing travel times to sound-speed perturbations is zero at the target location and maximum in a surrounding shell. This is unlike the deep-focusing amplitude measurements, which have maximum sensitivity at the target point. We compare the signal-to-noise ratio for travel-time and amplitude measurements for different types of sound-speed perturbations, under the assumption that noise is solely due to the random excitation of the waves. We find that, for highly localized perturbations in sound speed, the signal-to-noise ratio is higher for amplitude measurements than for travel-time measurements. We conclude that amplitude measurements are a useful complement to travel-time measurements in time--distance helioseismology.
18 pages, 10 figures
References in corpus (5)
- Meridional circulation in the solar convection zone: time-distance helioseismic inferences from four years of HMI/SDO observations
- Computational helioseismology in the frequency domain: acoustic waves in axisymmetric solar models with flows
- Generalization of the noise model for time-distance helioseismology
- The amplitude of the cross-covariance function of solar oscillations as a diagnostic tool for wave attenuation and geometrical spreading
- Deep-Focus Diagnostics of Sunspot Structure