Red Edge Characteristics and SPAD Estimation Model Using Hyperspectral Data for Rice in Ningxia Irrigation Zone

Chlorophyll content is an important parameter when assessing rice cultivation and production. In order to estimate chlorophyll content quickly and precisely, different nitrogen level experiments for Ninggeng 43 were conducted. Canopy hyperspectral reflectance and the SPAD value at different growth stages were measured. We analyzed the red edge characteristics of hyperspectral reflectance at the canopy level and built the SPAD estimation models. Our results revealed that the SPAD value increased with an increasing nitrogen level, and reached a maximum value at the booting stage and then drops. Spectral reflectance gradually became smaller in the visible wavelengths and bigger in the near infrared wavelengths with increasing nitrogen levels, there were 'red shift' and 'blue shift' phenomena from jointing to booting, before the filling stage for the red edge position, amplitude and region of the canopy spectra. All three red edge parameters increased with increases in the nitrogen level. The model with the red edge region area as the independent variable was determined to be the optimalfor the SPAD of the rice canopy at jointing stage, but for the booting and filling stages, the model based on red edge position was more reliable for predicting SPAD values.These results are a little different from rice in south China, using hyperspectral technology can quantitatively retrieve the SPAD values of rice at the canopy level, and therefore provide a theoretical basis for rice growth monitoring based on remote sensing.