Design and validation of portable optical instrument for crop diagnose

Abstract

In this paper, a portable diagnostic instrument was designed and tested, which can measure the normalized difference vegetation index (NDVI) and structure insensitive pigment index (SIPI) of crop canopy in field. The instrument have a valid survey area of 1 m*1 m when the height between instrument and the ground was fixed to 1.3 meter The crop growth condition can be assessed based on their NDVI and SIPI values, so it will be very important for crop management to get these values. The instrument uses sunlight as its light source. There are six special different photoelectrical detectors within red, blue and near infrared bands, which are used for detecting incidence sunlight and reflex light from the canopy of crop. This optical 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 the NDVI and SIPI value based on the A/D value. 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 RS232 serial interface. The prototype was tested in the crop field at different view directions. This paper also provided the method of calibration, the results showed that the average measurement error to SIPI value of instrument was 5.25% and the average measurement error to NDVI value in vegetation-covered region is 6.40%. It reveals the on-site and non-sampling mode of crop growth monitoring by fixed on the agricultural machine traveling in the field.