The Sun-Earth Lagrange point L4, which is called a parking space of space, is considered one of the unique places where solar activity and the heliospheric environment can be observed continuously and comprehensively. The L4 mission affords a clear and wide-angle view of the Sun-Earth line for the study of Sun-Earth connections from remote-sensing observations. The L4 mission will significantly contribute to advancing heliophysics science, improving space weather forecasting capability, extending space weather studies far beyond near-Earth space, and reducing risk from solar radiation hazards on human missions to the Moon and Mars. Our paper outlines the importance of L4 observations by using remote-sensing instruments and advocates comprehensive and coordinated observations of the heliosphere at multi-points including other planned L1 and L5 missions. We mainly discuss scientific perspectives on three topics in view of remote sensing observations: (1) solar magnetic field structure and evolution, (2) source regions of geoeffective solar energetic particles (SEPs), and (3) stereoscopic views of solar corona and coronal mass ejections (CMEs).

The Korean Solar Radio Burst Locator (KSRBL) is a solar radio spectrograph observing the broad frequency range from 0.245 to 18 GHz with the capability of locating wideband gyrosynchrotron bursts. Due to the characteristics of a spiral feed, the beam center varies in a spiral pattern with frequency, making a modulation pattern over the wideband spectrum. After a calibration process, we obtained dynamic spectra consistent with the Nobeyama Radio Polarimeter (NoRP). We compared and analyzed the locations of bursts observed by KSRBL with results from the Nobeyama Radioheliograph (NoRH) and Atmospheric Imaging Assembly (AIA). As a result, we found that the KSRBL provides the ability to locate flaring sources on the Sun within around 2′.