As the starting point for the identification of an observing mode that is best suited to a given scientific goal, observers should decide whether to carry out photometry, spectrophotometry or polarimetry. For photometry and spectrophotometry observers can choose among single pointing observations and a number of multi-pointing observations (raster, map, scan). Whereas the mapping mode is designed for complete sky coverage allowing for various oversampling intervals, a raster is simply a sequence of single pointing observations, for which complete sky coverage is not strictly necessary.
The decision tree in Fig. 9 and the following summary give an overview of all observing modes and AOTs. They should serve as quick guides for a first selection of possibly appropriate observing modes.
Figure 9: Overview of PHT AOTs.
Photometry
Single-Pointing and Staring Raster Modes
to 
using PHT-P detectors.
The user selects an
arbitrary number of filters (up to 14) and one aperture for each filter.
The apertures may vary between different filters. This AOT can be
used in the staring raster mode.
Scientific application: point source photometry of compact sources (e.g. comets, stars and galaxies) and spot photometry of extended sources. In staring raster mode: photometry of smooth and homogeneously extended (background) sources.
Section 6.4
to
using PHT-C detectors. The maximum number of filters is
11. No aperture selection is required as field of view is defined
by the area of the detector arrays. This AOT can be used in
staring raster mode.
Section 6.4
to using PHT-P detectors. A reference level is obtained
and absolute flux calibration is achieved
by chopping against the internal fine calibration source (FCS).
The user selects one filter and one aperture. Raster observations may be
performed.
Scientific application: absolute sky brightness photometry of e.g. Zodiacal Light, galactic background emission, extragalactic background light.
Section 6.4
to
using PHT-C detectors. No apertures are required as field
of view is determined by the area of the detector arrays.
Section 6.4
to
using PHT-P detectors. Only one filter can be
selected and the minimum number of apertures is 2.
Only single pointing observations can be accomplished, chopping is
possible.
Scientific application: extended emission around point sources, e.g. stellar discs and shells, nucleus/disc separation in galaxies.
Section 6.5
One-Dimensional Scanning Mode
See PHT32 below, which also has one-dimensional scanning modes as an option.
Two-Dimensional Mapping Modes
to using either the PHT-C100 or PHT-C200 detector arrays.
This is the standard mapping AOT for the PHT-C detectors, and it
is designed for complete sky coverage and high spatial resolution by
over-sampling. It is not available for solar system objects to be
observed in tracking mode.
Scientific application: far-infrared photometry and mapping of structured extended sources: dust clouds, star formation regions, galaxies.
Section 6.6
to
using PHT-P detectors. (to be used in connection with AOTs PHT18
and PHT19) A sequence of up to 30 positions is measured
which may be irregularly distributed within a field of 1.5 degrees
diameter. The user selects one aperture and one filter.
The detector remains switched-on all the time increasing its
stability and minimising the times for overheads.
The dynamic range of the detectors can be adjusted to the
brightness of each individual point. This AOT is not available for
solar system objects to be observed in tracking mode.
Scientific application: efficient photometry of clustered sources, e.g. proto - planetary discs in open clusters, galaxy clusters.
Section 6.7
to
using PHT-C detectors. No aperture selection is
required as field of view is defined by the area of the detector
arrays.
Section 6.7
Spectrophotometry
to 
and 6 to 
using the PHT-S
sub-instrument. Only one sky position can be measured.
Staring or chopped observations can be performed.
Scientific application: chemical composition of interplanetary, interstellar and intracluster dust; excitation stage of heating sources.
Section 6.8
Polarimetry
and using PHT-P detectors. The
target is observed with one aperture and one filter through
3 different polarisers having orientations of 0, 120 and 240
degrees, respectively.
Scientific application: point sources, e.g. non-thermal emission of AGN; extended sources, e.g. magnetic field structure by grain alignment in e.g. star formation regions.
Section 6.9
to using PHT-C detectors.
Section 6.9
In the Cookbook section (Sect. 6.4 to 6.9) all parameters required to fully specify the observations are given for each AOT since they are necessary to calculate approximate observing times. Note, however, that for the first phase of proposal submission (phase 1) not all parameters have to be explicitly included in the proposal. Details of the phases for proposal submission are described in the document ISO CALL FOR OBSERVING PROPOSALS.