Development of a light-emitting-diode-based bidirectional active remote-sensing system for monitoring crop growth

Abstract

Forward-biased light-emitting diodes (LEDs) emit a stable light with a narrow band of wavelengths and work well as photodiodes when reverse-biased. Unlike other photodiodes, LEDs are optically selective sensors that are most sensitive to the same band of wavelengths that they emit. This implies that LEDs can be utilized as potential optical filters, which are used to extract only lights of certain wavelengths when needed. In this study, we fabricated a bidirectional active two-band (635 and 825 nm) spectral radiometer with two different LEDs and evaluated its ability to monitor canopy growth of paddy rice (Oryza sativa). The LED radiometer consisted of LED sensors, an amplifier, and a data logger. The fabricated LED-based bidirectional active remote-sensing system (LED-BARSS) was calibrated by comparing the reflectance of each LED sensor with its counterpart on a commercial multispectral radiometer (Cropscan). Two correction methods (dark-millivolt correction and sun angle correction) were also employed. To monitor canopy growth, the normalized difference vegetation index (NDVI) was determined using the reflectance data obtained from the LED spectral radiometer at Chonnam National University, Gwangju, Korea. We found a strong linear relationship between the NDVI values obtained from the LED spectrometer and those from Cropscan. This suggests that the LED-BARSS could be used to monitor the physiological developments in paddy rice.