A vegetation canopy scatters and transmits a significant amount of NIR radiation towards the soil surface, irradiating the soil underneath as well as in between individual plants. A fraction of the NIR radiation incident on the soil, fraction that is determined by the optical properties of the soil surface, is reflected back towards the sensor and scattered and transmitted by the canopy. By contrast, red light is strongly absorbed by the uppermost leaf layers of the canopy, and irradiance at the soil surface is limited to that received directly from the sun and sky through canopy gaps