The wavelength selective mirror is a periodically structured diffraction grating with high reflectivity. The proportion of reflected radiation is the object's reflectivity or albedo. Absorptivity, reflectivity, and emissivity of all bodies are dependent on the wavelength of the radiation. Many reflective prisms use total internal reflection to achieve high reflectivity. Albedo features are areas of markedly different reflectivity, as seen by telescopic observation. An increase in cloud cover leads to higher albedo, or surface reflectivity, of the Earth. The amplitude modulation comes from moving surfaces of different reflectivity and angle of reflection. Cool roofs are defined as roofs with both high reflectivity and high thermal emittance. The shading coefficient depends on the color of glass and degree of reflectivity. Headlight reflectors rely on the excellent reflectivity of a thin film of rhodium. Ellipsometry is especially superior to reflectivity measurements when studying anisotropic samples. Reflectors vary enormously in size, colour, reflectivity and portability. Galinstan has higher reflectivity and lower density than mercury. The broadband mirror is usually coated with a low reflectivity coating to allow emission. The result is a map of radar reflectivity, including both amplitude and phase.