Electronic distance measurement — Geodimeter operating principle A Geodimeter measures distance primarily based on which carrier and modulation principle?

Introduction / Context:
Electronic distance measurement (EDM) instruments determine distance by measuring the phase or time of flight of a modulated carrier. Classical instruments split by carrier type: optical (light), infrared, or microwave. Knowing which instrument uses which carrier is a standard surveying MCQ topic.

Given Data / Assumptions:

• Geodimeter is one of the earliest EDM instruments.
• It uses an optical (visible light) carrier with intensity modulation.
• Tellurometer is the microwave counterpart; Distomat and others may use IR.

Concept / Approach:

Geodimeter employs a visible-light (optical) carrier, typically intensity-modulated and phase-compared upon return, to infer distance. While the optical carrier frequency is on the order of 10^14 Hz, the modulation frequency is low and measurable for phase comparison.

Step-by-Step Solution:

Verification / Alternative check:

Instrument taxonomy: Geodimeter (optical), Tellurometer (microwave), later IR EDMs (infrared). This mapping is standard in surveying texts and exam prep guides.

Why Other Options Are Wrong:

• (b) Over-specifies IR only; not the classical Geodimeter.
• (c) States a true attribute of visible light frequency but is not the operating principle itself.
• (d) Describes microwave EDM (Tellurometer), not Geodimeter.

Common Pitfalls:

• Confusing carrier frequency (optical) with modulation frequency (radio-range).
• Mixing up instrument names across carrier types.

Final Answer:

Propagation of modulated light waves (optical carrier).