5.20 Subexposures

In an Exposure Specification, each data sample collected is represented in APT by a separate entity called a subexposure. A subexposure tracks the orbit number (orbit_number) of the sample, as well as any override to the default duration (actual_duration). You need not supply these values.

5.20.1 Actual_Duration

Unless the user (or the Autoadjust feature in the Orbit Planner) fills in this field, it will be blank and defaults used. For example, if the exposure is CR-SPLIT, the sum of the exposure times of the subexposures will be equal to the parent exposure's exposure time. In all other cases the exposure time of each subexposure will be equal to the exposure time of the parent exposure.

Note, however, that if the actual_duration field is filled, this value overrides the default. So the total exposure time for an exposure will be equal to the sum of the actual_durations of the subexposures regardless of the original exposure time.

5.20.2 Orbit_Number

This determines which orbit the subexposure will be placed in. Generally, unless you need to control the orbit structure of the visit, this field can be left alone and will be filled in by the Orbit Planner.