PhoSim Tutorial 10: How to Generate Sequences of Images

In addition to generating single images or groups of images across multiple chip focal planes, PhoSim can also naturally generate time sequences under different observing conditions. A variety of physics including the weather/clouds, will correctly follow time correlations and patterns. 

A powerful aspect of the stars and galaxy module generator is that it is repeatable. This means that you can generate multiple catalogs and get the same set of stars & galaxies appearing at the same right ascension and declination. Thus, a simple catalog like the following would generate stars and galaxies covering a 0.1-degree-diameter circle.

The image from the first catalog is:

Then, if this were followed by a second catalog, like the one below, with the seed changed and the ID different (so the filenames are distinct), the same stars and galaxies would appear. However, the observing conditions (e.g. weather, airmass, filter etc.) would be different, so you would get a different-looking image for the same scene.

The image from the second catalog is:

There are many more complex uses of this. For instance, you could specify the exact time of the observations or the filter if you were simulating a pre-defined cadence. These additional parameters are optional, though. You could also specify an individual object along with the star and galaxy commands. The individual object could then appear only in some of the catalogs in order to simulate variability.