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.

More common:

• 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.