Analysis of the Velocity Field of CMEs Using Optical Flow Methods

Abstract

Optical flow is a powerful image processing tool for measuring motion in digital images. The optical flow algorithm provides an estimate of the velocity vector at every pixel from a pair of successive images. Here we present an application of this method to images of coronal mass ejections (CMEs). The technique is first tested and validated on a simulated CME. It is then applied to several CMEs observed with the LASCO C2 coronagraph to derive their velocity fields. The resulting velocity measurements allow us to visualize the evolution of the CME plasma and to separate the ``bulk'' velocity from the expansion velocity of a given CME. To our knowledge, this is the first time that such information has been extracted from CME observations. We discuss the limitations and accuracy of our optical flow method and propose further improvements.