ATMOSPHERE AND TERRAIN ENERGY INTERACTIONS

Radiant Energy

The capacity of electromagnetic radiation within a specified spectral band to do work, measured in Joules

Radiant Flux

The amount of radiant energy hitting, leaving, or passing through a surface per unit of time, measured in Watts

Irradiance

The radiant flux incident upon a surface per unit area, measured in Watts per square meter

Radiant Exitance

The radiant flux leaving a surface per unit area, measured in Watts per square meters

Radiance

The radiant intensity per unit of projected source area in a specified direction, measured in Watts per square meter per steradian

Steradian

A unit of solid angle that encompasses an area on a sphere equal to the square of its radius

Path Length

The distance light travels through the atmosphere, affecting the degree of energy attenuation.

Attenuation

The reduction or loss of radiant energy intensity as it travels through the atmosphere due to scattering and absorption.

Scattering

The unpredictable diffusion or redirection of electromagnetic energy by atmospheric particles.

Rayleigh Scattering

Molecular scattering caused by atmospheric gas particles that are smaller in diameter than the EMR wavelength, primarily affecting shorter wavelengths like blue light.

Mie Scattering

Non-molecular or aerosol scattering caused by particles (such as smoke or dust) with diameters roughly equal to the EMR wavelength, affecting longer wavelengths.

Non-Selective Scattering

Atmospheric scattering caused by large particles (such as water droplets or ice crystals) at least 10 times larger than the EMR wavelength, which scatters all wavelengths equally without preference.

Transmission

The passage of energy through a medium or atmosphere without being attenuated or reduced in intensity.

Absorption

The process in which radiant energy is taken up by atmospheric gases or terrain materials and converted into other energy forms.

Absorption Band

A specific region of the electromagnetic spectrum where energy is absorbed by a particular atmospheric substance or gas.

Atmospheric Window

A region of the electromagnetic spectrum that allows radiant energy to pass through and transmit effectively with little to no atmospheric absorption.

Refraction

The bending or deflection of electromagnetic radiation as it travels through atmospheric layers of varying optical densities.

Index of Refraction

The ratio comparing the speed of light in a vacuum to the speed of light within a specific material or atmospheric layer

Specular Reflection

The predictable, directional bouncing of radiation off a smooth surface at equal angles of incidence and exitance.

Diffuse Reflection

The scattering or reflection of radiation uniformly in many directions off a rough or Lambertian surface.

Lambertian Surface

A perfectly diffuse reflecting surface that distributes reflected energy equally in all directions regardless of the viewing angle.

Radiation Budget Equation

The mathematical expression balancing incident radiant flux against the sum of reflected, transmitted, and absorbed energy components.