A plant health sensing system was developed for determining nitrogen status in plants. The system consists of a
multi-spectral optical sensor and a data-acquisition and processing unit. The optical sensor’s light source provides
modulated panchromatic illumination of a plant canopy with light-emitting diodes, and the sensor measures spectral
reflectance through optical filters that partition the energy into blue, green, red, and near-infrared wavebands.
Spectral reflectance of plants is detected in situ, at the four wavebands, in real time. The data-acquisition and
processing unit is based on a single board computer that collects data from the multi-spectral sensor and spatial
information from a global positioning system receiver. Spectral reflectance at the selected wavebands is analyzed,
with algorithms developed during preliminary work, to determine nitrogen status in plants. The plant health sensing
system has been tested primarily in the laboratory and field so far, and promising results have been obtained. This
article describes the development, theory of operation, and test results of the plant health sensing system.