The reflectivity measures the fractional amplitude of the reflected electromagnetic field, and the reflection refers to the fraction of the incident electromagnetic power, which is reflected at the interface. This measurement is the square of the reflectivity value. The reflectivity is usually expressed as a complex number using the Fresnel equations for one layer, while the other is always a positive real number.
In photometry and heat transfer, reflectivity is the fraction of random radiation reflected by a given surface. This must be before being considered as a directional property, which is a function of the reflected direction, the direction of incidence and the incident wavelength. It is also often averaged over the reflected hemisphere to obtain a hemispherical spectral reflectivity. Reflectivity is an important concept in the field of solar thermal energy, telecommunications and radar.
In some areas of research, reflectivity differs from reflection by the fact that reflectivity is the value that applies to thick reflective objects. When reflection occurs on thin layers of material, internal reflection effects can cause fluctuations depending on the thickness of the surface. The reflectivity is a limiting value as the surface becomes thicker. The reflectivity is given without regard to other parameters, such as the reflection of the back surface, since reflectivity is a directional property; Most surfaces can be divided into those that are specific reflections, and those that are diffuse reflections.
For mirror surfaces such as glass or polished metal, the reflectivity will be close to zero at all angles, with the exception of the corresponding reflected angle. For diffuse surfaces, such as matte white paint, the reflectivity is uniform, and the radiation is reflected in all corners equally or almost equally. These surfaces are called Lambert surfaces.
If the surface exhibits Lambert reflection, the light incident on it is scattered so that the apparent brightness of the surface to the observer is the same regardless of the viewing angle of the surface. Although not all irregular surfaces are ideal Lambrot reflectors, this often gives a good approximation when other surface characteristics are unknown.
In computer graphics, Lambert reflection is often used as the basis for diffuse reflection. This method causes closed polygons to reflect light evenly in all directions when rendering. The effect from the perspective of the viewer is that rotating or scaling an object does not change the perceived brightness of the object's surface. However, in the real world, objects usually have some combination of diffuse and specular reflective properties. Reflection can be seen when light passes from a medium with one refractive index into one with another refractive index.
This part of the incident light, reflected from the body of water, is specular and is calculated using the Fresnel coefficients; Fresnel's reflection is directional. Therefore, it does not make a significant contribution to the albedo, which reflects the diffuse reflection of light. Reflectivity, assuming a flat surface, as required by the Fresnel equations, can be compensated for given the waviness. The generalization of the reflection to the diffraction grating, which is used to scatter light along the wavelength, is called diffraction efficiency.
