Reflectance

Reflectance is the fraction of incident electromagnetic radiation that a surface or material reflects. It varies with wavelength, angle, polarization, and the material’s condition.

Fresnel equations: Equations that calculate reflection and transmission of light at an interface between materials. They quantify how incidence angle and refractive indices determine interface reflectance.
Reflectance spectrum: A measurement or representation of reflectance as a function of wavelength. It shows how reflectance changes across the visible and other spectral regions.
Spectrophotometry: The measurement of how much light a sample reflects or transmits at different wavelengths. It produces quantitative reflectance measurements for materials and samples.
Hemispherical reflectance: The fraction of incident radiation reflected into the entire hemisphere above a surface. It totals reflected energy over outgoing directions rather than measuring one direction.
Refractive index: A measure of how light propagates through a material, including its phase velocity and absorption. The refractive indices on either side of an interface set its reflection behavior.
Absorptance: The fraction of incident radiation absorbed by a material. Together with reflection and transmission, it accounts for incident energy.
Remote sensing: The acquisition of information about objects or regions without direct physical contact, often using reflected radiation. Reflected sunlight enables satellite and airborne instruments to characterize Earth's surface.
Directional-hemispherical reflectance: The fraction of radiation arriving from one direction that a surface reflects into all outgoing directions. It captures total reflection for a specified incoming beam.
Specular reflection: Reflection in which light leaves a smooth surface in a defined direction. It concentrates reflected light directionally, unlike diffuse reflection.
Transmittance: The fraction of incident radiation transmitted through a material or interface. It distinguishes light passing through a sample from light reflected by it.

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