Spitzer Documentation & Tools
MIPS Instrument Handbook

Chapter 3      Operating Modes

There are four major operational modes (or Astronomical Observation Templates; AOTs) of the MIPS instrument:

· Scan Map (includes slow, medium and fast scan rates, where incomplete coverage at 160 µm is obtained at the fast scan rate).

· Photometry and Super Resolution (PH/SR; includes super-resolution, large source, and small source options, and can be used to obtain multiple images through the cluster and raster-map options).

· Spectral Energy Distribution (SED; can be used for a single spectrum or step and stare spectral mapping).

· Total Power Mode (TP; used to obtain absolute brightness measurements for highly extended sources).

Observing in any of these modes involved the acquisition of multiple data frames, not just a single frame.  The multiplicity of frames provides for rejection of cosmic rays, calibration of the Ge:Ga focal plane array data in the light of the two-time-constant behavior of those detectors, adequate sampling of the point spread function (PSF; especially for super resolution observations), and, in the case of the 160 µm array, for building up a filled image using multiple offset exposures of that 2x20 pixel array.  The total number of images obtained depends on the total integration time needed, the observational mode, and the array. 

 

For all AOTs, the number of cycles is the number of times the basic observing sequence or full map sequence was executed, as described below. Observers are reminded that in photometry/super-resolution mode, MIPS always took multiple, dithered frames, each with the specified exposure time.  Because of this, the total exposure time is an integer multiple of the single frame exposure time and the number of dither positions imposed on all photometry AORs; the total on-source integration time is quantized as a result.  The number of cycles selection determines how many of these integration-time quanta will be obtained.  Likewise, on-source integration time is quantized in scan-map mode, depending on the selected scan rate, and selecting more than one scan cycle will build up integration time in multiples of that single-cycle integration time.

 

Observers could specify that a small region (a raster map) be covered in photometry mode.  The entire AOT cycle is repeated at each raster map location; the number of map cycles is different and refers to the number of times the whole map is repeated.

 

Because of noise improvements relating to characteristics of the stressed Ge:Ga 160 µm detectors, when a 10 sec exposure time is selected, the 160 µm detectors were reset twice within the exposure interval.  This effectively resulted in two exposures at 160 µm before dithering when using the 10 sec exposure option.  The 160 µm sensitivities for 10 sec exposures include the multiple resets.

 

The Cluster Option was a way to conveniently specify repetitions of one or multiple observations at several closely grouped pointings (within approximately 1° of initial target).  The observations done at each cluster position are identical, and done in the same pointing sequences as for a single target AOR.  The observational modes that can be specified under the cluster option are MIPS Photometry/Super Resolution, SED, and TP. Also, observations of moving targets could be made in a co-moving frame for all MIPS AOTs, including Scan Map.