Define DOP and differentiate PDOP, TDOP, HDOP, VDOP.

• A. TDOP expresses horizontal geometry.
• B. VDOP measures velocity.
• C. PDOP is only about time performance.
• D. DOP expresses satellite geometry effects; PDOP for position, TDOP for time, HDOP for horizontal, VDOP for vertical.

Answer: (D)

DOP measures how satellite geometry affects how accurately a GNSS receiver can estimate its solution. The numbers tell you how geometry impacts different parts of the solution: PDOP reflects the overall position error in 3D, TDOP relates to the clock time error, HDOP focuses on horizontal (latitude/longitude) accuracy, and VDOP concerns vertical (height) accuracy. When satellites are well spread across the sky, DOP values are low and estimates are more precise; when satellites cluster or lie in a narrow arc, DOP values rise and errors grow even if the measurements themselves are clean. The statement that DOP expresses satellite geometry effects, with PDOP for position, TDOP for time, HDOP for horizontal, and VDOP for vertical, is the correct interpretation.