Evidence of hot spot directional signature from airborne POLDER measurements

The POLDER instrument was flown during the BOREAS experiment over various sites and at various altitudes in the Canadian boreal forest and other nearby targets. The instrument design permits the acquisition of the directional signature of any surface cover. In particular, the high directional resolution of POLDER allows it to measure, with an unprecedented accuracy, the hot spot signature of natural targets. The authors present some typical examples of such highly anisotropic reflectance directional signatures. The ratio of the maximum reflectance (hot spot direction) to the minimum reflectance (broad area in the forward scattering hemisphere) varies with wavelength and canopy. It can be as large as six in the visible and three in the near IR.