Spectral signature of olive groves in areas of east Lesvos, Greece. On the horizontal axis we have the central wavelength in nanometers (nm) and on the vertical axis the reflectance of foliage in W/m^-2/sr^-1/μm^-1. The most vigorous trees have higher reflectance in the infrared spectrum (760-900 nm). Moderate vigor trees have low reflectance values and then the unhealthy trees have the lowest reflectance.