a non-dimensional, unitless quantity that measures how well a surface reflects solar energy; ranges from 0 - 1; a value of 0 means the surface is a perfect absorber, where all incoming energy is absorbed, a value of 1 means the surface is a perfect reflector, where all incoming energy is reflected and none is absorbed. This quantity can also be expressed as a percent with a range from 0 to 100, with zero percent absorbing all incoming energy and 100 percent reflecting all energy.