A further result of extended rasters on Neptune has been the verification of the point spread function of the spectrometer. Remarkable agreement with predictions from telescope and instrument modeling has been found. A measurement for a typical spatial pixel of the PACS spectrometer can be compared in Figure 4.8 and Figure 4.9 to a convolution of a calculated PSF (from actual telescope model including known wave-front errors) with a square pixel of 9.4"x9.4".
Figure 4.8. Calculated spectrometer PSF at 62 µm (left) and measurement on Neptune (right) done at the same wavelength. Both are normalised to the peak and scaled by square-root, to enhance the faint wing pattern. The calculation includes the predicted telescope wave-front error, which dominates the overall aberrations.
