Goniopolarimetric inversion using SVD: An application to type III radio bursts observed by STEREO

Abstract

Type III radio bursts are intense solar radio emissions generated by beams of energetic electrons injected into the interplanetary medium. They can be routinely observed by the S/Waves instruments on‐board the STEREO (Solar Terrestrial Relation Observatory) spacecraft. We describe goniopolarimetric (GP) inversion of a signal measured on non‐orthogonal antennas using the Singular Value Decomposition (SVD) technique. This wave propagation analysis can be applied to spectral matrices built from measurements by the High Frequency Receiver (HFR; a part of the S/Waves experiment). We have found an empirical relation between the decomposed spectral matrices and apparent source sizes for waves with a low degree of polarization. Simulations of electromagnetic emissions with various senses and degrees of polarization, and source shapes show that SVD gives us reasonable results with respect to the polarization ellipsoid geometry. An error analysis considering inaccuracies of HFR has been performed in order to test the validity of the k‐vector direction estimation and the obtained empirical relation. We present a joint observation of a type III radio burst by the STEREO and Wind spacecraft during small separation distances. We obtain consistent results for the k‐vector direction and apparent source size using different analysis methods for the measurements of the STEREO and Wind spacecraft. We demonstrate that SVD can be an effective tool for the wave analysis of radio emissions measured on non‐orthogonal antennas even with very extended sources.