Bias in velocity determinations from full-disk solar observations

Abstract

Estimates for the global solar surface velocity field can be obtained from time series of full-disk solar images. However, bias is introduced by mistakes in the assumptions about the geometry of the observations, and by imperfections in the optical system. I investigate many sources of bias and determine their first-order influence on the measured velocity field (both the transverse and longitudinal components). Results are presented in analytical and pictorial form. By comparing bias velocities of unknown origin with the results, one may obtain clues to the cause of the bias.