Measuring method for photosynthetic photon flux density using a digital camera

Abstract

The paper presents a method for measuring photosynthetic photon flux density (PPFD) using a commercially available digital camera. PPFD is one of the critically important measurements to control photosynthetic reaction of plants. Conventionally a dedicated quantum sensor is used to measure PPFD. A quantum sensor, however, can measure PPFD of a target point at once. Thus considerable cost and labor would be consumed if the quantum sensors were introduced for managing photosynthetic reaction of numerous plants in a large greenhouse for growing commercial crops. In order to solve the problem, we propose a method for measuring PPFD using a commercially available digital camera. The method estimates spectral irradiance of daylight, fluctuating hour by hour according to weather condition changes, on the basis of the color information of a reference object in an image captured by a digital camera. Then PPFD is derived from the estimated spectral irradiance. For practical use, plural reference objects are placed in a plant community and captured as an image. PPFDs at the positions of the reference objects in the captured image are simultaneously measured. We believe that proposed method is useful in real cultivation. We conducted experiments in outdoor environment. During the experiments, a Nikon digital SLR camera D300 and a white plaster ball as a reference object were used. We finally confirmed that the average error rate of PPFD measurements by this method was 2.58%, and the maximum was within 5% which is equivalent to the accuracy of the quantum sensor on the market.