Fuente: Wipo "precision farming" A handheld sensor is disclosed. The sensor has a microcontroller, a current pulse control unit coupled to a light emitting diode (LED), and a photodiode. The microcontroller controls the current pulse control unit to provide a pulsed illumination of a target plant and the photodiode reads the magnitude of the reflectance from the target plant. The microcontroller accepts the reading from the photodiode and computes a normalized difference vegetative index (NDVI) based at least on the reading.