Positions of the apparent sources localised by BELLA compared to the expected scattering-free positions determined by the Parker density model. The localisations are shown in polar coordinates (a) and Cartesian coordinates (b) for the readers’ convenience. An Archimedean Parker spiral is a linear function in polar coordinates; the linear trend in panel (b) shows that the BELLA-localised sources are consistent with the path of a Parker spiral. The fitted spiral results in a solar wind velocity of V_sw = 492.98 ± 6.19 km s⁻¹ and a source longitude of ϕ₀ = 74.62° ±1.25°.