Which set of factors does NOT influence GNSS observation time?

• A. I, II and III
• B. II, III and IV
• C. I, II and IV
• D. I, III and IV

Answer: (D)

The key idea here is that how long you observe in GNSS is about collecting enough usable data to meet the required solution quality. The duration is driven mainly by satellite availability and the geometry of the visible satellites. If the constellation is favorable, you can finish sooner; if there aren’t enough or the geometry is weak, you need to observe longer to accumulate enough observations.

Factors that affect the accuracy or quality of each observation—like atmospheric conditions, multipath, receiver noise, and the need for corrections—change how good your result is, but they don’t typically force you to extend the observation length to obtain a solution, unless you’re specifically trying to mitigate those errors with more data. The one factor that does influence how long you must observe is satellite availability/geometry, since poor visibility or poor geometry requires more time to reach the target reliability.

So the set that does not influence the observation time consists of the environmental and processing-related factors, while the duration itself is governed by satellite availability and geometry.