Surface Reflectance/Bidirectional Reflectance Distribution Function

Light interacts with physical matter by being either absorbed by it, reflected from it, or passed through it, depending on the structural and chemical composition of the object’s surface. Measuring the radiant flux reflected from an object, relative to the radiant flux received by it therefore allows conclusions about the chemical or structural composition. Earth science has long used this principle for characterizing earth surface properties through optical remote sensing. However, light received by satellite sensors orbiting our planet has passed through Earth’s atmosphere twice before it is being recorded. Reflectance measured at the top of the atmosphere (TOA) is therefore a function not only of the composition of the earth surface, but also the earth’s atmospheric conditions as well as the geometric configuration of sun, earth, and observing instrument. This is because surface properties are typically not Lambertian, thus the reflectance measured at the sensor will depend on the angle with which the reflected light beam hits the target. Disentanglement of the contributions of both aerosol properties and surface bidirectional reflectance effects is not trivial and can formmajor obstacles for accurate inference of surface properties.