Multi-band photodiode sensor

A method for managing the irrigation of plants comprising the steps of:

• a) providing the multi-band sensor in the vicinity of plants within a target control area subject to irrigation, the multi-band sensor comprising:
• 1) an infrared thermometer effective for remotely measuring a surface temperature of a plant canopy or soil;
• 2) a multi-photodiode array effective for measuring surface reflectance of a plant canopy or soil within the near infra-red, red, green, and blue regions, comprising the region from 880±50 nm to 450±40 nm, said surface reflectance being measured using ambient sunlight;
• 3) a microprocessor in communication with and effective to receive and store measured data from said infrared thermometer, and said surface reflectance data from said multi-photodiode array;
• b) measuring and collecting surface temperature data for a plant canopy or soil at time (t) and designating the measured temperature Tsurf(t), and collecting spectral reflectance data in the near infrared, red, green and blue bands from said multi-band sensor for said target control area;
• c) transmitting said temperature data and spectral reflectance data to a remote microprocessor-based computer control unit;
• d) correcting said temperature data and spectral reflectance data for the sun angle at which it was collected;
• e) evaluating the corrected temperature data and spectral reflectance data to determine if they were collected from soil or plant canopy by calculating normalized difference vegetative index (NDVI) at time (t) to get NDVI(t), and identifying NDVI for a soil type in a target irrigation management zone to determine a value designated NDVIsoil, wherein if NDVI(t) is less than or equal to NDVIsoil, then corrected Tsurf(t) is not used to calculate said crop canopy temperature in evaluating the spectral reflectance data to determine if the plant canopy is diseased or healthy, and determine if the plant is diseased or healthy, and
• 1) if the data are from a plant canopy, evaluating the spectral reflectance data to determine if the plant is diseased or healthy, if the plant is diseased, optionally withholding irrigation;
• 2) if the plant is healthy, evaluating the temperature data to determine if the plant is water-stressed;
• and
• 3) generating an irrigation signal for irrigation or automatically initiating irrigation if the plant is water-stressed.