Coronal Streamer Brightness Profiles Investigated with BriLo Using Parker Solar Probe White-Light Data

We present the Brightness-Location (BriLo) method, a novel single-spacecraft technique which exploits the Thomson scattering theory for localizing extended coronal features such as streamers using white-light (WL) imaging. Beyond determining the longitude and latitude of coronal features, the method also provides estimates of their geometrical properties, such as angular width (column depth). Validation is performed through geometrical triangulation with multi-viewpoint coronagraphs (the Solar TErrestrial RElations Observatory A COR2 and the Solar and Heliospheric Observatory C2-C3). The method is applied to ten coronal streamers observed by the Wide-Field Imager for Solar Probe (WISPR) on board the Parker Solar Probe (PSP) between encounter 1 - 17. We applied BriLo to two different data products, L3 and LX, which differ in K-corona treatment and absolute brightness levels. The L3 and LX results show good agreement in deriving streamer directionality, with differences of 2 - 30° in longitude and 1 - 6° in latitude. Both datasets provide longitude and latitude estimates that are broadly consistent with triangulation results. We further classified streamers and compared their locations with potential-field source surface (PFSS) extrapolations of the heliospheric current sheet (HCS). Helmet streamers are generally found close to the HCS, whereas pseudostreamers in proximity to active regions. In conclusion, the application of BriLo to LX data yields realistic streamer widths of several to ten degrees, while L3 data produce unrealistically narrow values below one degree. This discrepancy arises from the line of sight (LOS) integration of the observed signal and the dependence of F-corona removal on background estimation and coronal conditions. Overall, BriLo proves to be a robust tool not only for streamer localization but also for assessing and validating WL imaging techniques.