survey depth

The phrase survey depth indicates how far an astronomical survey reaches, but is cited using different measures. The obvious measure of distance (parsecs or light-years) is probably most often used for explanations for public consumption, e.g., news releases, presumably estimated from those more commonly used for scientific purposes, which include:

• largest apparent magnitude number reached, often specifying bands.
• exposure time, i.e., length of time used to image each part of the survey field, using measures of seconds (or kiloseconds), hours, or days, or sometimes for space observatories, orbits.
• highest redshift reached or targeted.

A survey may also have a minimum reach, and the term survey depth might be used for a specification of both maximum and minimum, or for the difference between maximum and minimum. Such a declared minimum could be because of the restriction of atmospheric windows on ground-based observation, or could merely be because the survey is targeting a particular era of the universe.