ON THE RELIABILITY OF RING DIAGRAM ANALYSIS

A comparison between the results of applying a ring diagram analysis t o two data sets is described in order to check the quality of the two sets and the reliability of the method. The series used have been obta ined with two different helioseismological instruments with the same s patial resolution. A section of 30 x 30 deg(2) about the disk center h as been tracked during 512 minutes over a series of images taken simul taneously by the Taiwan Oscillation Network instrument station at the Observatorio del Teide and the Michelson Doppler Imager on board the S olar and Heliospheric Observatory. Three-dimensional power spectra hav e been constructed from both series and fitted to get horizontal veloc ity flows as a function of frequency. Finally, an inversion process ha s been applied to obtain the depth dependence of the average velocity vector in a depth range of 0-25 Mm below the solar surface. The result s show an acceptable correlation between the velocities obtained from the fitting of the spectra of both data sets in spite of the different kinds of noise affecting the two instruments. However, the correlatio n drops when comparing the velocities obtained after the inversion pro cess based on these results.