Which method is used to study the effects of Earth's gravitational field from space-based observations?

• A. SATELLITE GRAVITY, from orbits
• B. GRAVIMETRY, from surface gravity
• C. ASTROGEODETIC DEFLECTIONS, from triangulation
• D. Seismology

Answer: (A)

Studying Earth's gravitational field from space relies on how gravity shapes the motion of a satellite in orbit. By precisely tracking a satellite’s position and velocity over time, scientists detect tiny variations in its orbit caused by differences in gravity across the planet. From these orbital perturbations, a global map of the gravity field is produced. This approach, satellite gravimetry, directly leverages space-based observations because the gravity field is inferred from the satellite’s orbital behavior, not from measurements taken on the ground or from distant reflections.

Surface gravity measurements (taken at ground level) don’t involve space-based observations. Deflections in astrogeodetic measurements would rely on observing how gravity bends light or signals, which isn’t the same as mapping the gravity field from orbit. Seismology uses seismic waves to image Earth's interior, not to measure the gravity field from space.