.

Yang, X., et al. (2016). "Seasonal variability of multiple leaf traits captured by leaf spectroscopy at two temperate deciduous forests." Remote Sensing of Environment 179: 1-12. Collection covers all the seasons. Summer is expected to have less variations on the plant's phonology. However, when the model was trained by a season data and then tested to the other seasons, the summer model showed the least RMSE. It means summer was the best season to collect leaves with divers status. It's harsh light must affect various level of stress to sunltis and shaded leaves.

Daughtry, C.S.T., Walthall, C.L., Kim, M.S., de Colstoun, E.B. and McMurtrey, J.E., 2000. Estimating corn leaf chlorophyll concentration from leaf and canopy reflectance. Remote Sensing of Environment, 74(2): 229-239. Background effects, such as LAI and soil, interfere the leaf signal. Using double indices -ratio of indices sensitive to background to those sensitive to foliar traits - would contribute to reduce redundant signals.