Several concepts for canopy hotspot measurements from space have been investigated. The most promising involves active illumination and bistatic detection that would allow hotspot angular distribution （BRDF） measurements from space in a searchlight mode. The concept includes a pointable illumination source

such as a laser operating at an atmospheric window wavelength

coupled with a number of high spatialresolution detectors that are clustered around the illumination source in space

receiving photons nearly coaxial with the retroreflection direction. Microwave control and command among the satellite cluster would allow orienting the direction of the laser beam as well as the focusing detectors simultaneously so that the coupled system can function like a search light with almost unlimited pointing capabilities. The concept is called the HotSpot SearchLight （HSSL） satellite. A nominal satellite altitude of 600 km will allow hotspot BRDF measurements out to about 18 degrees phase angle. The distributed are taking radiometric measurements of the intensity wings of the hotspot angular distribution without the need for complex imaging detectors. The system can be operated at night for increased signaltonoise ratio. This way the hotspot angular signatures can be quantified and parameterized in sufficient detail to extract the biophysical information content of plant architectures.