Name the two main GNSS observation types and summarize their characteristics.

• A. Pseudorange (code) observations provide range with meter-level precision; carrier-phase observations provide phase data enabling centimeter- to millimeter-level precision with ambiguity resolution.
• B. Pseudorange observations provide phase data enabling centimeter-level precision; carrier-phase observations provide range with meter-level precision.
• C. Pseudorange and carrier-phase observations both provide centimeter-level precision without ambiguity resolution.
• D. Carrier-phase observations provide only code-like measurements; pseudorange provides phase data.

Answer: (A)

Two main GNSS observation types are the pseudorange (code) measurements and the carrier-phase measurements. Pseudorange uses the coded signal to estimate how long the signal took to travel from satellite to receiver, giving a distance with meter-level precision in typical standalone use. Carrier-phase looks at the phase of the carrier wave itself, and because phase can be measured with much finer resolution, it can reach centimeter- to millimeter-level precision—but you must determine the exact number of whole cycles between satellite and receiver, the integer ambiguities, to convert that phase information into a true range. Resolving these ambiguities is essential for the high-precision results. The pseudorange measurements provide robust, coarse range data, while carrier-phase measurements enable very high precision once ambiguity resolution is achieved. The other statements mix up which measurement type yields code versus phase information or claim high precision without ambiguity resolution, which doesn’t fit the true characteristics.