Validation of counter-streaming flows: (a, b) λ304 Å, (c, d) λ171 Å, (e, f) λ193 Å, and (g, h) λ211 Å. We show a region of 32 Mm × 32 Mm (region B in Fig. 4). The left images (a, c, e, and g) show the summed image of each wavelength over the two-hour time series superposed with the horizontal velocity vectors derived with LCT. The right images (b, d, f, and h) display a map of the angle Φ , which indicates the direction of the velocity vector (left is shown in blue and right in red). The white contour outlines the filament as seen in Hα.