Design of A Hyperspectral Nitrogen Sensing System for Citrus

Abstract. Citrus is one of the most important agricultural crop in Florida. Heavy reliance on agricultural chemicals and low fertilizer efficiencies have raised environmental and economic concerns. In this study, a system to sense nitrogen levels in a single citrus leaf was developed. Based on chlorophyll and protein spectral absorption bands, the sensing system’s wavelength ranges were chosen to be 620-950 nm and 1400-2450 nm. A reflectance housing was designed to block environmental noise and to ensure single leaf measurement. A halogen light source, two detector arrays, linear variable filters and a data acquisition board with a 16-bit ADC were used. The designed system had no moving parts, so it would be robust and resistant to vibration. The spectral resolution was less than 30 nm. The test results also showed that the sensing system had good signal-to-noise ratio and linearity. The visible (VIS) detector had linearity (r >0.99), and the near infrared (NIR) detector also had linearity (r>0.999). The stability of the VIS detector was within ±0.1%, and the stability of the NIR detector was within ±0.5%.