On the feasibility of correlation tracking at moderate resolution

Abstract

The SOUP experiment demonstrated that photospheric surface flows can be measured by correlation tracking of white-light intensity features at high resolution (November et al., 1987). In order to assess the feasibility of this technique with observations made at lower resolution, we have applied it to the same SOUP data artificially degraded, but still free of seeing distortion. Comparison with the velocity structures inferred from the original data shows generally good agreement when the resolution is better than about 2″. The radial outflow from a sunspot penumbra, however, can only be seen with resolution of better than 1″. With resolution of worse than 2″, the inferred velocity fields rapidly lose coherence, while resolution of better than 1″ yields little improvement. We conclude that apertures as small as 10–14 cm on a space-based platform will be useful for the measurement of large-scale horizontal motions.