Which of the following satellite orbits is most suitable for obtaining moderate-to-high spatial resolution images of the same location on Earth at a fixed local solar time repeatedly?
- AGeostationary orbit
- BSun-synchronous polar orbitCorrect
- CHighly elliptical orbit
- DLow-inclination equatorial orbit
Solution
Concept
Characteristics of sun-synchronous polar orbits
Formula
Ωdot = 360 deg / 365.25 days approx 0.9856 deg/day
Step-by-step solution
1. High-resolution land monitoring requires consistent solar illumination angle across revisits to eliminate sun-angle artifacts. 2. Sun-synchronous polar orbits precess eastward at roughly 0.986 degrees per day to match Earth's annual solar journey. 3. This maintains a fixed local solar crossing time across successive orbits, making option B the correct answer. Answer: B
Explanation
A sun-synchronous polar orbit is uniquely suited for land-cover mapping because its orbital plane precesses at the same rate as Earth rotates around the sun. This ensures the satellite crosses every latitude at the same local solar time, providing constant sun illumination and shadow conditions essential for consistent multi-temporal optical imagery. Hence, option B is correct.
Why the other options are wrong
A) Geostationary satellites stay fixed over the equator at 35,786 km and provide coarse spatial resolution, mostly for meteorology. C) Highly elliptical orbits (e.g. Molniya) serve high-latitude communications. D) Equatorial orbits cannot cover mid to high latitude global land masses.
Shortcut
Sun-synchronous = Fixed sun angle & polar pass; Geostationary = Fixed above equator (36,000 km).
Common mistake
Selecting geostationary orbit, which is located at ~35,786 km above the equator and cannot provide high spatial resolution polar/global land cover.
Correct answer: B) Sun-synchronous polar orbit