DEVELOPMENT OF A SOLAR-INDUCED CHLOROPHYLL FLUORESCENCE DETECTING INSTRUMENT BASED ON FRAUNHOFER LINE PRINCIPLE

摘要

The solar-induced fluorescence from plant canopies can be detected from field radiance spectra based on the Fraunhofer line principle. In this paper, a portable solar-induced chlorophyll fluorescence detecting instrument based on this principle was designed and tested. The instrument has a valid survey area of 1.3 X 1.3 when the height between instrument and the ground was fixed to 1.3 meter. The instrument uses sunlight as its light source. There are 2 sets special different photoelectrical detectors with the center wavelength at 760nm and 771nm respectively and every detector's bandwidth is 1nm. Both sets of detectors are composed of a upper detector which are used for detecting incidence sunlight and a bottom detector which are used for detecting reflex light from the canopy of crop. This instrument includes photoelectric detector module, signal process and A/D convert module, the data storing and transmission module and human-machine interface module. The detector is the core of the instrument which measures the spectrums at special bands. The microprocessor calculates solar-induced fluorescence value based on the A/D values get from detectors. And the value can be displayed on the instrument's LCD, stored in the flash memory of instrument and can also be uploaded to PC through the PC's serial interface. The prototype was tested in the crop field at different view directions and the results demonstrate that the instrument can measure the solar-induced chlorophyll value exactly with the correlation coefficients was 0.9 compared to the values got from Analytical Spectral Devices FieldSpec Pro NIR spectrometer. It reveals the on-site and non-sampling mode of crop growth monitoring by fixed on the agricultural machine traveling in the field. This instrument can diagnose the plant growth status by the acquired spectral response.