What does the D in DGPS stand for?

The correct answer is Differential. The term DGPS stands for Differential Global Positioning System. This system enhances the accuracy of GPS signals, which can be subject to errors due to atmospheric conditions, satellite orbital variations, and other factors. By using a network of fixed ground reference stations that know their exact positions, DGPS calculates the difference between the known positions and the positions given by GPS. The corrections are then transmitted to GPS receivers, which apply them to improve the overall accuracy of the position data.

In this context, the other terms do not accurately reflect the specific technology that DGPS refers to. For instance, while "Dynamic" could imply a real-time system, it does not capture the essence of the differential corrections used in DGPS. "Digital" pertains to the type of signals rather than the correction method. Similarly, "Directional" suggests a focus on orientation rather than position accuracy, which is not the primary goal of DGPS. Thus, Differential is the most accurate and contextual choice regarding the purpose and function of the system.