Effects of maize tassel at the heading stage on radiation transfer characteristics of canopy reflectance

In order to analyze the influence of maize tassel on the radiation transmission characteristics of visible and near infrared band at the heading stage of maize, 4D rail crane system was applied for 2 consecutive years in maize at the heading stage in Huailai Experimental Station in Hebei. The experiment was carried out respectively at the beginning of the heading and the end of the 3 tassel gradients. The maize canopy reflectance characteristics at the heading stage and the characteristics of male tassel dry matter content were analyzed. The results showed that: 1) the measured canopy reflectance rate was higher than the simulated value at the beginning of heading, and the simulated value of the model was higher than the measured value at the late stage of development of the growth period. However, in the visible band, the measured values were higher than the simulated values at the whole heading stage, and in the near infrared band, the simulated values were higher than the measured values. 2) By analyzing the characteristics of bidirectional reflectance of different tassel gradient canopy, we found that in visible light band, reflectance without tassel in the directions of solar main plane and vertical solar main plane was the highest, followed by half tassel and the lowest in whole tassel; in near infrared band, reflectance was not different for the 3 tassels treatments in the direction of solar main plane, however, the reflectance in backward scattering direction was higher than that of forward scattering direction, and the reflectance of tassel-free was still higher than that of half tassel and whole tassel. The same results were obtained under vertical observation conditions. 3) The correlation between the simulated value of PROSAIL model and agricultural parameters showed that the simulated value had a significant negative correlation with chlorophyll content (LCC) and leaf area index (LAI), and the measured and simulated values without tassel were highly consistent with the correlation between LCC and LAI. 4) The total fresh weight of tassel in the whole heading stage of maize varied but the difference in total dry weight was not significant. The water content of tassel decreased from 80% at the beginning to 10% at the end of tassel, indicating water content should be considered for model establishment. The research on the radiation transmission characteristics of tassel at maize heading stage on canopy would be helpful in modifying radiation transmission model and improving the accuracy of simulation.