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

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)

Measuring how gravity changes the motion of orbiting satellites allows mapping Earth's gravity field from space. By tracking a satellite’s precise position and velocity (and, in some missions, the distance between two satellites), scientists infer variations in the gravitational potential over the globe. These measurements are inverted to produce gravity models that show how mass is distributed inside the Earth and on its surface, including temporal changes from oceans, ice, and groundwater. Ground-based gravimetry only samples local points on the surface, so it doesn’t provide the global, space-based perspective. Deflections of light due to gravity relate to general relativity and astrometric measurements, not direct mapping of the gravity field via orbital dynamics. Seismology probes interior structure with waves, not the satellite-based gravity field.

Measuring how gravity changes the motion of orbiting satellites allows mapping Earth's gravity field from space. By tracking a satellite’s precise position and velocity (and, in some missions, the distance between two satellites), scientists infer variations in the gravitational potential over the globe. These measurements are inverted to produce gravity models that show how mass is distributed inside the Earth and on its surface, including temporal changes from oceans, ice, and groundwater. Ground-based gravimetry only samples local points on the surface, so it doesn’t provide the global, space-based perspective. Deflections of light due to gravity relate to general relativity and astrometric measurements, not direct mapping of the gravity field via orbital dynamics. Seismology probes interior structure with waves, not the satellite-based gravity field.