preliminary investigation; preliminary survey
A formal term for an initial fact-finding step before a full-scale study, inspection, or research project.
We conducted a preliminary investigation before the full-scale survey.
We will revise the plan based on the results of the preliminary survey.
事前調査 also means a preliminary or advance investigation, but 予備調査 emphasizes a preparatory or pilot nature, often as a smaller-scale step before the main research.
Compound of 予備 (yobi, 'preparatory, reserve') and 調査 (chōsa, 'investigation, survey').