9.5.6 Visualization

We can and should use Spot's visualization tools to verify that the observation is doing what we think it is doing. Our whole region will fit in one retrieval of an ISSA image; see §9.4 for instructions on image retrieval. After retrieving an ISSA image (or any other image), to visualize the observations we have planned, highlight the AOR, go to the ``Overlays'' menu and select ``Current AOR on current image.'' It will calculate visibility windows and ask when you want to visualize; pick any time where the ONC is visible. It will then overlay the map on the region you have selected. (To avoid common errors during this process, be sure that you have retrieved an image of the desired target as opposed to a different target in your list, then be sure that you have selected the appropriate AOR such that the ``current AOR'' refers to the target whose image you have retrieved.) Because this particular map is so large and dense, it is likely to take some time for Spot to render it. While this visualization is turned on, the rest of Spot could be sluggish. Be patient! See Figure 9.12 for what it should display. Note that on the right hand side of the image window, when we added the overlay, a layer appeared with the label of the AOR. The symbols are, from left to right, a check mark (to turn on and off), a $\times$ (to remove the overlay entirely), a small red and blue table (to get a listing of each pointing), and a crosshairs (to turn on and off the visualization of each wavelength).

Figure 9.12: Visualization of MIPS observation.

The three wavelengths are represented by blue $(24 \; \mu {\rm m})$, green $(70 \; \mu {\rm m})$ and pink $(160 \; \mu {\rm m})$. The overscan regions discussed above can clearly be seen on the edges of the map. By clicking on the crosshairs icon on the right side of the ISSA window, we get a dialog box enabling us to turn off and on the visualization for each wavelength. Be patient; it may take a little while for the computer to respond. If we have a lot of computer RAM, we can try animating the scan to see exactly what it's doing. In order to do this, we click on the small red-and-blue table icon on the right edge of the ISSA image window to get a listing of each pointing. Select ``Animation'' or ``Animation with Trail'' to watch it step through the mapping procedure. Note that specifically for MIPS scan maps, this is not for the impatient or those with limited RAM (``faint of RAM''?). To turn off the visualization (or animation) after verifying that it's doing what we think it's doing, click on the $\times$ under the name of the observation in the ISSA window. Note how much faster Spot runs now!

Note: Had this been an observation in which we expected to get $160 \; \mu {\rm m}$ data, because it is an extended object, we should have requested three more passes in two sets of two pairs (for a total of 4) to make sure that the $160 \; \mu {\rm m}$ data are high-quality and includes no asteroids. Moreover, since it is a bright extended object, we should be sure to have sufficient low background observations before and after the object to ensure a good calibration; see ``extrapolated stims'' section in the MIPS Data Handbook for more information.

The observation as currently designed takes about 1.5 hrs, and we can go up to three hours in a single MIPS AOR. We might want to design an AOR to cover a larger area. We can play with the values in the AOT window, hitting ``Calc. Obs. Time'' after each change. If we design an observation that exceeds 3 hours, Spot will tell us. In order to figure out the area covered by the AOR, we can use the tools within Spot. Under the ``Overlays" menu, there is a ``distance tool'' option. By clicking and dragging, we get the distance measured in arcseconds. (The measurement appears near where you clicked before dragging. Click on the little red and blue ``table'' icon to change the display color or units of the measurement.) By following this general process, we discover that we can make a $1^{\circ} \times 1^{\circ}$ map that takes less than 3 hours; see Figure 9.13.

Figure 9.13: MIPS Scan Map AOT window, final values for the planned observation.

Now, we're done with the MIPS part of the survey, and we should move on to IRAC. Before we do, though, let's consider another option for the MIPS scan map, covering an even larger region.