Their approach, scholarly but accessible, was aided by their first-hand observation of many of the places and objects that were featured.

Where data and first-hand observation are concerned, what's the context?

First-hand observation determines the truth or falsity of a given statement.

Considering the shortness of their stay their account reveals very intensive first-hand observation.

These first-hand observations and experiences are among my happiest and sharpest memories, and probably account for the many nature form subjects in my sculpture.