摘要: Using a full range hand-held spectrometer (350 nm 2500 nm), this study examined the temporal profile of the spectral signature of rice crop (Oryza sativa L.). It also, examined the effects of illumination geometry for hyperspectral measurements in rice paddies. The study area was located in Axios river plain (Greece), one of the most extended and highly productive rice cultivation areas in Mediterranean ecoregions. The spectral data were collected from a set of 24 experimental plots cultivated with indica type rice, each of them under different fertilisation treatment on eleven different dates during 2014 and 2015 seasons; in total 264 spectral measurements were recorded. Reflectance from the rice paddies showed not to be influenced from the distance of the device from the plot at nadir, but only by the viewing angle, the distance off nadir, and the aspect. The variance between different treatments was found to be about 14% on average, with the maximum variance (35%) recorded on the 80th day after sowing. Comparison of signature shapes between plots, growth stages, or diachronically, was based on the 1st-order derivative of the signatures. Plotting the temporal profile of different indices together with a time series of four rice crop biometrics allowed identification of a time interval of 10 days as optimum for spectra recordings. The perspectives of the study can be seen in the establishment of a protocol of hyperspectral data collection in rice paddies using portable spectrometers and assisting in the use of hyperspectral cameras mounted on unmanned aerial vehicles towards precision farming and rice crop monitoring.
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