Correlation between the Shallow U-Net velocity fields and the ground truth. Panels (a1), (b1) and (c1) are the pixel-to-pixel correlations between the ground-truth v_x and the model estimated v_x by the three shallow U-Net models. Colors in these panels depict the number densities of points at each coordinate, with warmer colors for higher number densities. Black dashed lines are the corresponding linear fit results, with their functions displayed on the top left corner of each panel. Panels (a2), (b2), and (c2) are similar to panels (a1), (b1), and (c1) but for v_y. Panels (a3), (b3), and (c3) are the distribution of the angles between the ground-truth velocity fields and the estimated velocity fields by the three shallow U-Net models.