This study developed an approach for remote estimation of Vegetation Fraction (VF) and Flower Fraction (FF) in oilseed rape, which is a crop species with conspicuous flowers during reproduction. Canopy reflectance in green, red, red edge and NIR bands was obtained by a camera system mounted on an unmanned aerial vehicle (UAV) when oilseed rape was in the vegetative growth and flowering stage. The relationship of several widely-used Vegetation Indices (VI) vs. VF was tested and found to be different in different phenology stages. At the same VF when oilseed rape was flowering, canopy reflectance increased in all bands, and the tested VI decreased. Therefore, two algorithms to estimate VF were calibrated respectively, one for samples during vegetative growth and the other for samples during flowering stage. The results showed that the Visible Atmospherically Resistant Index (VARI green ) worked most accurately for estimating VF in flower-free samples with an Root Mean Square Error (RMSE) of 3.56%, while the Enhanced Vegetation Index (EVI2) was the best in flower-containing samples with an RMSE of 5.65%. Based on reflectance in green and NIR bands, a technique was developed to identify whether a sample contained flowers and then to choose automatically the appropriate algorithm for its VF estimation. During the flowering season, we also explored the potential of using canopy reflectance or VIs to estimate FF in oilseed rape. No significant correlation was observed between VI and FF when soil was visible in the sensor's field of view. Reflectance at 550 nm worked well for FF estimation with coefficient of determination (R 2 ) above 0.6. Our model was validated in oilseed rape planted under different nitrogen fertilization applications and in different phenology stages. The results showed that it was able to predict VF and FF accurately in oilseed rape with RMSE below 6%.

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, "Using remotely sensed spectral reflectance to indicate leaf photosynthetic efficiency derived from active fluorescence measurements," J. Appl. Remote Sens. 11(2), 026034 (2017), doi: 10.1117/1.JRS.11.026034. Abstract. Chlorophyll fluorescence (ChlF) is an important signature of photosynthesis to evaluate plant response to the environment. We explored an approach to estimate an important leaf ChlF-derived parameter, the intrinsic efficiency of photosystem II photochemistry (F v ∕F m ), using spectral indices calculated from leaf reflectance measured by a hyperspectral radiometer. It is observed that leaf chlorophyll content closely related to F v ∕F m in nonstressed leaves, thus the indices developed for chlorophyll estimation were successfully used to estimate F v ∕F m . For leaves under short-term stress, F v ∕F m dropped dramatically while leaf chlorophyll content remained almost the same. Compared to leaf chlorophyll content, reflectance was more sensitive to F v ∕F m variations. As F v ∕F m decreased, the slope of reflectance in the spectrum range of 700 to 900 nm obviously increased, and the first derivative reflectance in the red edge and infrared (NIR) regions was highly correlated with F v ∕F m . The indices using longwave red edge and NIR reflectance (NDRE 740 and CI 740 ) worked well for F v ∕F m retrieval in both stressed and nonstressed leaves with the coefficients of determination (R 2 ) above 0.72 and normalized root-meansquare errors below 0.16. Note that the relationships NDRE 740 and CI 740 versus F v ∕F m were significantly different between nonstressed and stressed leaves, which may give a good implication to detect short-term stress occurrence.