Landsat satellites use a sun-synchronous orbit crossing the equator at approximately 10:00 AM local time. What is the primary advantage of maintaining the same local crossing time?
AIt maximizes the amount of sunlight reaching the sensor
BIt ensures consistent solar illumination geometry across dates, making multi-temporal comparisons valid
CIt avoids orbital decay caused by atmospheric drag
DIt prevents the satellite from passing over the same area twice
Consistent local time means consistent sun angle, shadow length, and illumination intensity across repeat passes. This is critical because differences in reflectance between dates should reflect actual surface change, not varying illumination geometry.
Question 2 True / False
A geostationary weather satellite can image the same hemisphere every 10-15 minutes, but its spatial resolution is typically 0.5-4 km. This coarser resolution compared to low-earth-orbit satellites exists because geostationary orbit altitude is approximately 36,000 km.
TTrue
FFalse
Answer: True
Spatial resolution is inversely related to altitude for a given sensor aperture. At 36,000 km, each detector element covers a much larger ground area than the same detector at 700 km. The trade-off is temporal resolution versus spatial detail.
Question 3 Short Answer
Why do most land-observation satellites use near-polar sun-synchronous orbits rather than equatorial orbits?
Think about your answer, then reveal below.
Model answer: Near-polar orbits allow the satellite to observe nearly every point on Earth as the planet rotates beneath it, providing global coverage. An equatorial orbit would only image a narrow band around the equator. The sun-synchronous variant adds constant local solar time at each latitude, ensuring repeatable illumination conditions. The slight inclination (~98 degrees) causes the orbital plane to precess at exactly the rate Earth orbits the Sun.
Global coverage plus consistent illumination makes sun-synchronous polar orbits the standard for land and environmental monitoring missions.