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Implementation and Comparison of Acoustic Travel-Time Measurement Procedures for the Helioseismic and Magnetic Imager Time-Distance Helioseismology PipelineThe Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO) satellite is designed to produce high-resolution Doppler velocity maps of oscillations at the solar surface with high temporal cadence. To take advantage of these high-quality oscillation data, a time-distance helioseismology pipeline has been implemented at the Joint Science Operations Center (JSOC) at Stanford University. The aim of this pipeline is to generate maps of acoustic travel times from oscillations on the solar surface, and to infer subsurface 3D flow velocities and sound-speed perturbations. The wave travel times are measured from cross covariances of the observed solar oscillation signals. For implementation into the pipeline we have investigated three different travel-time definitions developed in time-distance helioseismology: a Gabor wavelet fitting (Kosovichev and Duvall, 1997), a minimization relative to a reference cross-covariance function (Gizon and Birch, 2002), and a linearized version of the minimization method (Gizon and Birch, 2004). Using Doppler velocity data from the Michelson Doppler Imager (MDI) instrument on board SOHO, we tested and compared these definitions for the mean and difference travel-time perturbations measured from reciprocal signals. Although all three procedures return similar travel times in a quiet Sun region, the method of Gizon and Birch (2004) gives travel times that are significantly different from the others in a magnetic (active) region. Thus, for the pipeline implementation we chose the procedures of Kosovichev and Duvall (1997) and Gizon and Birch (2002). We investigated the relationships among these three travel-time definitions, their sensitivities to fitting parameters, and estimated the random errors they produce
Document ID
20100031217
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Couvidat, S.
(Stanford Univ. Stanford, CA, United States)
Zhao, J.
(Stanford Univ. Stanford, CA, United States)
Birch, A. C.
(Northwest Research Associates, Inc. Boulder, CO, United States)
Kosovichev, A. G.
(Stanford Univ. Stanford, CA, United States)
Duvall, T. L., Jr.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Parchevsky, K.
(Stanford Univ. Stanford, CA, United States)
Scherrer, P. H.
(Stanford Univ. Stanford, CA, United States)
Date Acquired
August 25, 2013
Publication Date
January 1, 2009
Subject Category
Solar Physics
Funding Number(s)
CONTRACT_GRANT: NAS5-02139
Distribution Limits
Public
Copyright
Other

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