Final answer:
The correct option is b. The highest level of commercial navigational accuracy is provided by the Precise Positioning Service (PPS), ensuring both high precision and high accuracy for military and authorized users.
Step-by-step explanation:
The highest level of commercial navigational accuracy is provided by Precise Positioning Service (PPS). GPS measurements can vary in terms of precision and accuracy, which are critical concepts in navigation and positioning. Precision refers to how closely multiple measurements or estimates are to each other, whereas accuracy refers to how close a measurement is to the true or actual value.
For example, when a GPS system attempts to locate a restaurant that is at the center of a bull's-eye, accurate measurements would be close to the center, even if they are not close to each other, indicating high accuracy but low precision. Conversely, precise measurements would be grouped closely together, but they may be far from the center, indicating high precision but low accuracy. The PPS is reserved for military and authorized users and provides the most precise positioning details, surpassing other services such as Standard Positioning Service (SPS), Differential GPS (DGPS), and Wide Area Augmentation System (WAAS).