IPA IP 2024 Question 99
A question IPA Japan published in 令和6年度 ITパスポート試験 公開問題 問99, translated into English. ITPEC is based on the same exams.
Which of the following achieves higher positioning accuracy by taking an orbit that stays over a specific region for a relatively long time and by being used together with GPS, so that positions can be measured even in places where it is difficult to catch GPS radio waves, such as between tall buildings and in narrow alleys?
Explanation
Quasi-zenith satellite — a positioning satellite whose orbit keeps it high over one region for hours at a time, so it adds to GPS where GPS signals are blocked.
GPS positioning needs signals from at least four satellites. Between tall buildings or in a narrow alley, satellites low in the sky are hidden, and too few can be received. Quasi-zenith satellites, such as Japan's Michibiki (QZSS), fly an inclined orbit that keeps one of them close to straight overhead of the region for long periods, and a signal from near the zenith reaches the street even among buildings. They transmit GPS-compatible signals, so a receiver uses them as extra GPS satellites, and they also broadcast correction data that raises the accuracy further.
Answer (c)
Why not others:
- •(a) Assisted GPS — a phone gets the satellites' orbit data and its rough position through the mobile network to find its position faster; it adds no satellite and takes no orbit
- •(b) Gyro sensor — detects angular velocity (rotation), for example to keep estimating a car's position where satellite signals are lost; it is a sensor on the ground, not in orbit
- •(d) Probe car — a vehicle that sends its position and speed as traffic data; it uses positioning rather than providing it
Key rule: Satellite positioning improves with more satellites in view; a quasi-zenith satellite adds one that is nearly overhead, where buildings block it least.
Networks · AI-written, may contain errors
This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.