Which statement best captures what remote sensing measures: interaction and/or emission of electromagnetic radiation from a target?

Introduction / Context:
Remote sensing captures the radiative signature of targets. This signature arises from how targets interact with incident radiation (reflection, absorption, scattering) and from their own emission (especially in the thermal infrared). Understanding both pathways is essential for interpreting imagery and retrieving geophysical variables.

Given Data / Assumptions:

• Passive optical sensors depend on reflected sunlight.
• Thermal sensors measure emitted longwave radiation related to temperature and emissivity.
• Active sensors (radar, lidar) measure returned energy after interaction with the target.

Concept / Approach:
Targets interact with incoming EM energy via reflection (specular/diffuse), absorption, and scattering, altering the spectrum and intensity recorded by the sensor. In addition, targets emit radiation according to their temperature and emissivity (Planckian behavior for thermal IR). Hence, remote sensing encompasses both interaction with incident radiation and self-emission, depending on wavelength and sensor type.

Step-by-Step Solution:
Identify key mechanisms: reflection/scattering/absorption and emission.Recognize that sensors capture the net radiance reaching the detector.Conclude that both interaction and emission are relevant and measured.

Verification / Alternative check:
Thermal IR images at night demonstrate pure emission-based sensing; daytime VNIR images show reflection dominance. Radar (active) measures interaction via backscatter.

Why Other Options Are Wrong:

• Only interaction or only emission is incomplete.
• 'Neither' contradicts the fundamental operation of remote sensing.
• 'Only reflection' excludes emission and active sensing returns.

Common Pitfalls:
Assuming optical remote sensing equals reflection only; ignoring emissivity and temperature effects in thermal imagery.

Final Answer:
Both (a) and (b)