Plasma structure extraction from lasco images by the dual-tree complex wavelet transform

Abstract

Images of the Sun obtained in distinct electromagnetic ranges can be very useful to investigate electrodynamical processes that occur in this star. This work analyzes the application of a two-dimensional version of the Dual-Tree Complex Wavelet Transform (DTCWT) to highlight physical features in the Large Angle and Spectrometric Coronograph images. The importance of those features is that they are related with coronal ejections of magnetized solar plasma, which can produce geomagnetic disturbances at the Earth. The DTCWT is a laborious improvement of the well-known Discrete Wavelet Transform (DWT) with additional properties of shift invariance, ability to analyze multiple directions for multidimensional signals, and computationally efficient algorithms. The multilevel decomposition of an image with the DTCWT generates complex wavelet coefficients, which are manipulated for providing a proper visualization of the plasma structures, highlighting features, and helping further analyses. The methodology implemented here is of interest to space weather laboratories and has been shown to be a very useful tool to a better identification and characterization of the features related to magnetized plasma phenomena in the solar corona.