Which of the following best describes almanac data?

• A. The weather data used to calibrate GPS signals.
• B. Information the GPS receiver can obtain from one satellite describing the approximate orbital positioning of all satellites in the constellation.
• C. The time and date information used to synchronize the GPS receiver with GPS time.
• D. The precise clock error of each satellite's atomic clock.

Answer: (B)

Almanac data provides coarse orbital information for all GPS satellites, broadcast by the satellites to help the receiver quickly know where to look for each satellite and plan acquisitions. It lets you predict approximate satellite positions for days ahead, so you can acquire satellites faster when you start tracking or reacquire after a loss of lock. This data is not about weather or timing synchronization, nor does it give the precise clock error for each satellite—that level of precision comes from the ephemeris data associated with individual satellites. Since the statement describes the constellation-wide, approximate orbital information obtainable from one satellite, it best matches the purpose of almanac data.