First Aug.

J. Atherton , C.J. Nichol, A. Porcar-Castell. Using spectral chlorophyll fluorescence and the photochemical reflectance index to predict physiological dynamics. Remote Sensing of Environment. 2016, 176: 17-30.

Firstly, I have to say this paper is quite hard to understand, because not only it involves a lot of biology knowledge and terms, but also the author missed a lot of commas, making it difficult to punctuate.

Anyway, this paper presents a framework that links physiological fluorescence theory with spectral remote sensing measurements at the leaf scale.

As you can see, the study built a system to observe leaf both passively and actively.

This study proves that by coupling canopy scale radiative transfer models to dynamical biological process-based models, optical measurements (chlorophyll fluorescence and PRI) can potentially be linked to physiological parameters (such as ΦPSII). Consequently track short term fluctuations of leaf physiological situation.

But I believe, actually, the canopy level will be much more problematic.