Method: Estimating the upward motion vector (previous frame, current frame) a)Pass frames to the Farneback algorithm to estimate the overall motion vector (previous frame, current frame); b) Apply the following selection criteria: Subtract all vectors with magnitude <2 Pixels $(\Vert {\overrightarrow{\alpha }}_n\Vert <2)$; Subtract all vectors that have a Y component >0 (pointing downward).