Amplitude (upper row) and Doppler (lower row) fits to the IRIS (panel a), IRIS with SPICE PSF and pixelization (“IRIS synthetic SPICE”; panel b), and SPICE (panel c). Before fitting, the IRIS data on the left were first binned down 2 × 2 to better match the SPICE pixel size. Both the “synthetic SPICE” and real SPICE Doppler (panels b and c) show clear ridge artifacts that are absent from the IRIS Doppler (panel a). Some specific artifacts are highlighted. Comparison with the amplitudes in the upper row shows that these artifacts are associated with bright features in intensity. The elongated, rotated effective y − λ PSF causes bright intensity features to alias into Doppler, as further discussed in the text.