Sectional views of the photosphere evolution in velocity space for our fiducial model, as seen by observers at different viewing angles. The line of sight is oriented vertically downward in each plane, and only the cross-section through the ejecta center is shown. Here, v_∥ and v_⊥ represent the velocity components parallel and perpendicular to the line of sight, respectively. Colored lines indicate the photospheric contours at various epochs following the WD–NS merger.