Air photo scale sensitivity: Which factor does NOT affect the scale of vertical aerial photographs?

Introduction / Context:
The scale of a vertical aerial photograph is the ratio of a photo distance to the corresponding ground distance. It is governed by the camera geometry and the effective flying height over terrain. This question asks which listed factor does not affect scale.

Given Data / Assumptions:

• Vertical (or near-vertical) photography with known focal length f.
• Flying height above mean terrain H varies with topography.
• Ground elevation differences cause local scale variation.

Concept / Approach:
For vertical photos, average scale S ≈ f / H, where H is the flying height above the ground point (not sea level). Thus, focal length directly affects S; greater f increases scale (larger features). Flying height inversely affects scale. Ground elevation changes H locally, altering local scale. Therefore, all three listed factors a–c affect scale, meaning “None of these” is the correct response to “does not affect.”

Step-by-Step Solution:
Recall S ≈ f / H for vertical photos.Focal length f ↑ ⇒ S ↑ (larger scale).Flying height H ↑ ⇒ S ↓ (smaller scale).Ground elevation modifies local H ⇒ local scale variation across relief.Therefore, none of the listed a–c can be said to “not affect” scale; choose “None of these”.

Verification / Alternative check:
Relief displacement and scale variation are key reasons for orthorectification; DEMs are used to correct for ground elevation effects on scale and geometry.

Why Other Options Are Wrong:
Focal length/flying height/ground elevation each demonstrably change scale via S ≈ f/H.Any one of a–c marked as “does not affect” would contradict basic photogrammetry.

Common Pitfalls:
Confusing atmospheric clarity with geometric scale; while haze affects radiometry, it does not change geometric scale.

Final Answer:
None of these.