Chlorophyll Estimation Using Multi-spectral Reflectance and Height Sensing

Chlorophyll concentration relates strongly to the photosynthetic potential of a plant and subsequently to physiological and metabolic status of the plant. Chlorophyll is an indirect indicator of nitrogen status and is used in optical reflectance-based variable rate chemical application technology. This research investigated a non-destructive method of determining chlorophyll content and concentration at the individual plant level in spinach. A multi-spectral imaging system was used to determine spectral reflectance and to estimate top-view surface area. An ultrasonic distance sensor provided vegetation height estimates. Surface area estimates and height data were combined to estimate plant biomass. The relationships between reflectance, estimated biomass, and laboratory measured chlorophyll content and concentration were investigated. The product of biomass estimate and normalized difference vegetative index (NDVI680) provided the best estimate of chlorophyll content per plant (r2 = 0.91) while estimates of chlorophyll concentration per unit leaf mass were poor (r2 = 0.30).

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