Illustration of the SPICE PSF issue in the y − λ plane. The PSF is tilted in the y − λ plane as shown in panel (b), causing leakage of signal from bright features to adjacent pixels, not strictly at the same y or λ values, as shown in panels (c) and (d). Measurements of Doppler velocity from the data in panels (c) and (d) would lead to artificial Doppler shifts, as shown in Figure 2.