Experiences with the Use of the Local Correlation Tracking Method when Studying Large-Scale Velocity Fields

Recently, we have used the local correlation tracking (LCT) method for mapping horizontal velocity fields in the solar photosphere [Švanda et al, 2005]. The method was applied to processed full-disc dopplergrams acquired by the MDI instrument on board the SoHO observatory. Now, the reliability of this method is verified on synthetic dopplergrams obtained by a very simple numerical simulation of the supergranular pattern. A series of synthetic dopplergrams was stretched by the known vector field and the LCT was applied. The results were compared with the original vector field. Applying the LCT method on synthetic data we got an important experience in the behaviour of this method when used on full-disc dopplergrams. On the basis of the described tests we assume that the use of LCT on full-disc dopplergrams provides sufficiently reliable results, so that method could be used for mapping the large-scale velocities with resolution 60 and an accuracy 10 m s.