## Abbreviations  
The following abbreviations are used in this manuscript: \begin{tabular}{l l} \(\alpha\) & The half apex angle \\ \(\alpha_{\text{s}}\) & Shadow fractions (equal to \(\text{P}_{\text{S}}\)) \\ \(\rho\) & Canopy reflectance from Unispec-DC \\ \(\rho_{\text{r}}\) & Radiance of the canopy sensor \\ \(\rho_{\text{i}}\) & Irradiance of the canopy sensor \\ \(\rho_{\text{iDC}}\) & Daytime DC for irradiance \\ \(\rho_{\text{rDC}}\) & Daytime DC for radiance \\ \(\xi\) & Angle between the sun and the viewer \\ \(\theta\) & Solar zenith angle \\ \(\theta_{v}\) & View zenith angle \\ \(\Omega\) & The value of clumping index \\ \(\gamma\) & The needle-to-shoot area ratio \\ APAR & Absorbed photosynthetically active radiation \\ APAR\({}_{\text{sun}}\) & Photosynthetically active radiation absorbed by sunlit leaves \\ APAR\({}_{\text{sh}}\) & Photosynthetically active radiation absorbed by shaded leaves \\ BRDF & Bidirectional reflectance distribution function \\ CERN & Chinese Ecosystem Research Network \\ \end{tabular} \begin{tabular}{l l} CHM & Canopy height model \\ \(C_{i}\) & The intercellular CO\({}_{2}\) concentration \\ CI & Clearness index \\ CV & Coefficient of variation \\ DC & Dark current \\ DOY & Day of year \\ EC & Eddy covariance \\ FIP & The first intersection point \\ FPAR & The fraction of PAR \\ \(\mathrm{fAPAR_{chl}}\) & The fraction of PAR absorbed by chlorophyll \\ G(\(\theta\)) & The projection of unit leaf areas \\ GPP & Gross primary production \\ GOST & Geometric-optical model \\ Ha & The height of the lower part of the tree (trunk space) \\ Hb & The height of crown \\ LAI & Leaf area index \\ L\({}_{\mathrm{sun}}\) & Sunlit leaf area index \\ L\({}_{\mathrm{sh}}\) & Shaded leaf area index \\ LUE, \(\epsilon\) & Light use efficiency \\ MODIS & Moderate Resolution Imaging Spectroradiometer \\ NADPH & Reduced pyridine nucleotide \\ NDVI & Normalized difference vegetation index \\ NEE & Net ecosystem productivity \\ NPQ & Nonphotochemical quenching \\ PAR & Photosynthetically active radiation \\ PQ & Photochemical quenching \\ PRI & Photochemical reflectance index \\ PRI\({}_{\mathrm{b}}\) & Big-leaf PRI \\ PRI\({}_{\mathrm{inv}}\) & Inversely calculated PRI at each view angle \\ PRI\({}_{\mathrm{obs}}\) & Observed PRI at each view angle \\ PRI\({}_{\mathrm{sh}}\) & PRI of shaded leaves \\ PRI\({}_{\mathrm{sun}}\) & PRI of sunlit leaves \\ PRI\({}_{\mathrm{t}}\) & Two-leaf PRI \\ PS I, II & Photosystem I and II \\ PTU & Pan-tilt unit \\ \(P_{T}\) & The observed fraction of sunlit leaves \\ \(P_{S}\) & The observed fraction of shaded leaves \\ \(P_{VG}\) & The observed fraction of background \\ \(P_{G}\) & The observed fraction of sunlit background \\ \(P_{Z}\) & The observed fraction of shade background \\ QYZ & Qianyanzhou Experimental Station \\ r & The diameter of the crown \\ R\({}_{0}\) & The extraterrestrial radiation at the top of the atmosphere \\ R\({}_{\mathrm{can}}\) & Canopy reflectance \\ R\({}_{\mathrm{T}}\) & Reflectance of sunlit leaves \\ R\({}_{\mathrm{G}}\) & Reflectance of sunlit background \\ R\({}_{\mathrm{S}}\) & Reflectance of shaded leaves \\ R\({}_{Z}\) & Reflectance of shaded background \\ \(R_{dif}\) & The ratio of diffuse radiation to total radiation \\ \(R_{e}\) & Daytime ecosystem respiration \\ R\({}_{\mathrm{g}}\) & The global solar radiation on the surface of the earth \\ R\({}_{\mathrm{leaf}}\) & Leaf reflectance \\ R\({}_{\mathrm{SL}}\) & The ratio of canopy reflectance to leaf reflectance \\ \end{tabular}