Estimation of Foliar Pigment Concentration in Floating Macrophytes using Hyperspectral Vegetation Indices

The peer-reviewed and edited version of this article was published in Volume 34, Issue 22 of the International Journal of Remote Sensing in 2013. The final publication is available at Taylor & Francis via http://www.tandfonline.com/doi/abs/10.1080/01431161.2013.828183Foliar pigment concentrations of chlorophylls and cartenoids are important indicators of plant physiological status, photosynthesis rate and net primary productivity. Although the utility of hyperspectral derived vegetation indices for estimating foliar pigment concentrationhas been documented formany vegetation types, floating macrophytes have not been assessed despite their ecological importance. This studysurveyed 39 wetland species (12 floating macrophytes (FM), 8 grasses/sedges/rushes(GSR) and 19 herbs/wildflowers (HWF)) to determine whether foliar pigments concentrations could be estimated from hyperspectral reflectance. Hyperspectral reflectance of samples was recorded using an ASD FieldSpec3 Max portable spectroradiometer with the plant probe attachment orvia a typical laboratory setup. A semi-empirical relationship was established using either alinear, second-degree polynomial or logarithmic function between 13 candidate vegetation indices and Chl-a, Chl-b, Car and Chl-a+bpigment concentrations.Vegetation indices R-M, CI-Red and MTCI were strongly correlated with foliar pigment concentrations using a linear fitting function. Chl-a+band Chl-b concentrations for all samples were reasonably estimated by the R-M index (R2: 0.66 and 0.64), although Chl-a and Car concentration estimates using CI-Red were weaker (R2: 0.63 and 0.51).Regression results indicate that pooled samples to estimate individual foliar pigments were less correlated than when each type of vegetation type was treated separately.For instance, Chl-a+bwas best estimated by CI-Red for FM (R2: 0.80), MTCI for HWF (R2: 0.77) and R-M for GSR (R2: 0.67). Although floating macrophytes feature unique adaptions to their aquatic environment, their foliar pigment concentrations and spectral signatures were comparable to other wetland vegetation types. Overall, vegetation indices that exploit the red-edge region werea reasonable compromise that had good explanatory power for estimation of foliar pigments across the sampled wetland vegetation types with CI-Red the best suited index for floating macrophytes