Joint Science Operations Center (JSOC) Data Products

Time Distance Products

Time-distance helioseismology pipeline generates subsurface horizontal flow-field maps and wave-speed perturbation maps for full-disk Sun and for selected active regions. All results are obtained from an 8-hour period, and covers 30° x 30° horizontally and 0 -- 20 Mm in depth.

Algorithm For Calculation:

The basic procedure for the time-distance data-analysis pipeline is as follows:

Track the HMI observed Dopplergrams with a local Snodgrass rotation rate, and map the area into a heliographic coordinate using Postel's projection. The tracked datacube usually has a dimension of 512 × 512 × 640, with a 0.06° sampling scale and 45-second cadence, covering a 30° × 30° area with a duration of 8 hours.
Phase-speed filtering is then applied to the datacube, and acoustic travel times are calculated from the cross-correlation functions. Two types of travel times are obtained using two different fitting algorithms:

Gabor wavelet fitting and
Gizon-Birch fitting method.

Inversions are performed based on Multi-Channel Deconvolution method, with two different sensitivity kernels employed: ray-path approximation kernel and Born-approximation kernel.

Thus, our products include two sets of acoustic travel times and four sets of inversion results in both flow fields and wave-speed perturbation fields.

Available Data products

Full-disk Data Products

For full-disk data, 25 areas are selected and are processed separately. Each day is divided into three 8-hr periods: 00:00 -- 07:59UT, 08:00 -- 15:59UT, and 16:00 -- 23:59UT. For each of these 25 areas and for each time period, we provide fitted travel times and inverted flow fields and wave-perturbations.

hmi.tdVtimes_synopHC are fitted travel times, with 'gabor' from Gabor wavelet fitting and 'GB' from Gizon-Birch defined travel times. Users can download either one or both.
hmi.tdVinvrt_synopHC are inversion results, with 'vx' for subsurface east-west direction velocity, 'vy' for subsurface north-south direction velocity, and 'cs' for subsurface wave-speed perturbations. Keywords 'Gabor' and 'GizonBirch' define which fitted travel times are used, and 'Born' and 'Raypath' define which sensitivity kernels are used.
Full-disk flow map and wave-perturbation map are then made by merging these 25 areas. Data sequence yet to be defined.
Active Region Data

References

Detailed procedure and description of results can be found in the paper :
Time-Distance Helioseismology Data-Analysis Pipeline for Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results

For details of the travel-time fittings and comparion of different fitting methods, please refer to the paper:
Implementation and Comparison of Acoustic Travel-Time Measurement Procedures for the Solar Dynamics Observatory/Helioseismic and Magnetic Imager Time-Distance Helioseismology Pipeline

Time Distance Products

Algorithm For Calculation:

Available Data products

References

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