This turret type scans deep into the ground, and detects all naturally occuring resources within its scanning range. It can be automated if mobile. The Surveyor turret is especially suited for detecting hostile entities. Such turret types are manadatory in order to see hostile forces approaching, as well as their attacks. Offensive turrets usually lack the necessary scanning range to see where they are shooting and depend on this turret type to reside in the vicinity.
Surveyor vehicles and towers serve two purposes: Their most immediate purpose lies in detecting previously unknown natural resources. Their second, arguably more important purpose lies in detecting changes in underground terrain. Regular radars have very limited capacity to penetrate the ground. Surveyors, on the other hand, can scan deep into the ground to detect new caves and hostile units.
Surveyor vehicles may be automated to search for new resources on their own, prioritizing the vicinity of terraformer vehicles. This should not be done, however, in the proximity of known hostile entities that are not currently present in the form of actual contacts or ghosts (the surveyor can only avoid what is visible in the client game state).