3.1.6 Photometry - 160 µm, Large Source (Large Field)
Figure 3.9: Photometry of a 4´x5.3´ region at 160 µm. A first sequence of measurements uses the scan mirror to offset the field by 2.5´ and the spacecraft to make smaller offsets to provide a filled 2´x5.3´ photometry region with a similar sky region. Compare with Figure 3.8. The spacecraft is then maneuvered to provide a second set of measurements on the opposite side of the source.
If the source to be measured is large, then a procedure similar to the 70 µm large-source one is used: first a 2´x5´ target field and corresponding sky field are imaged, then a telescope offset allows imaging of a second target field abutting the first, along with an additional sky field. This results in a fully sampled image over a ~ 4´x5´ field, as illustrated in Figure 3.9. This large-source AOT cycle at 160 µm provides only one fully sampled image of the source. In order to obtain good results, observers were strongly encouraged to specify at least four cycles of the large-source 160 µm AOT, so that redundancy can be used to reject artifacts in the images. Figure 3.10 shows how the large-source AOT can be used to image a moderately large target, and the placement of the individual images relative to such a target. If multiple cycles of the AOT were requested by the observer, they were automatically dithered to provide sampling on 1/2 pixel centers. Stimulator flashes are inserted at the beginning, middle and end of the sequence to calibrate the data, but are not shown in the figures.
Figure 3.10: The data acquisition sequence for the 160 µm large-source option. See also Figure 3.9. The image and sky data are acquired by a series of mirror motions (source to sky) and spacecraft motions to fill in the field of view. The sequence goes from left to right and top to bottom. The current array field of view is shown in red (or bold) and already acquired fields are shown in green (or light).