Abstract:
Chlorophyll is substance in vegetation for photosynthesis, ultimately affecting the net primary production, which can also indicate the healthy condition of vegetation living in a stressed environment. Hyperspectral remote sensing can provide a possibility for quick and accurate estimation of vegetation chlorophyll concentration in large areas. Soybean canopy reflectance data collected with ASD spectroradiometers (350~1050 nm), which were cultivated in water—fertilizer coupled control conditions, and chlorophyll content data were collected simultaneously. First, correlation between reflectance, derivative reflectance against chl-A and chl-B was conducted; second, RVI, RARSa and PSSRb regressed against chl-A and chl-B; and finally, ANN-BP was established for soybean chlorophyll concentration estimation, which had different nodes in hidden layers. It was found that soybean canopy reflectance shows a negative relationship with chl-A and chl-B, while it shows a positive relationship with chl-A and chl-B in near infrared region. Reflectance derivative has an intimate relationship with chl-A and chl-B in blue, green and red edge spectral region, with the maximum correlation coefficient in red edge region. Chlorophyll specified absorption vegetation index has intimate relationship with chl-A and chl-B, with regression determination coefficient
R2 greater than 0.736. ANN-BP model can greatly improve soybean chlorophyll concentration estimation accuracy. Determination coefficient (
R2=0.94) obtained with four nodes in hidden layers, however,
R2 still can be improved with nodes in hidden layers increasing, and
R2 reached 0.98 with six nodes in hidden layers. By above analysis, it indicated that, ANN-BP model can be applied to in-situ collected hyperspectral data for vegetation chlorophyll content estimation with quite accurate prediction, and in the future, ANN-BP model still should be applied to hyperspectral data for other vegetation biophysical and biochemical parameters estimation.