An investigation into robust spectral indices for leaf chlorophyll estimation

Remote sensing bio-control damage on aquatic invasive alien plant species

“…In the near infrared region (NIR) (700-1300nm), plants under stress, exhibit a low reflectance owing to extensive damage to the cellular structure of the leaf (Carter, 1993). The red-edge region is characterised by an abrupt change in reflectance between the VR (670nm) and NIR (800nm), caused by the combined effects of strong chlorophyll absorption in the red wavelengths and high leaf structure-driven reflectance in the NIR (Main et al, 2011). In the short wave infrared region (SWIR) (1300-2500nm) incident radiation is both reflected and absorbed with reduced absorption, centered at 1400nm and 1900nm (Huang and Apan, 2006).…”

“…Decades of research has been undertaken to identify biochemically sensitive regions that can be exploited to form vegetation indices (Main et al, 2011). Differences in reflectance between healthy and stressed vegetation due to changes in chlorophyll content primarily occur in the green region and red-edge region (Ustin et al, 2009).…”

“…A study conducted by Dennison et al (2009) caused by defoliation was apparent despite partial defoliation within the study area. However, the application of broadband NDVIs are limited by their instability owing to variations in canopy structure, illumination and viewing angle (Main et al, 2011). Additionally, broadband NDVIs asymptotically approach a saturation level after a Leaf Area Index (LAI) of approximately four; therefore overestimating the vegetation condition (Seller, 1985;Mutanga and Skidmore, 2004).…”

“…However, chlorophyll indices are generally species specific as the size, shape, surface and internal structure of the leaves vary from one plant species to another (Zhang et al, 2008). Ideally, the goal for researchers would be to develop vegetation indices that are not only as sensitive as possible to the desired parameter, but also robust across plant species and leaf structures (Main et al, 2011). Inorder to improve the robustness and generality of chlorophyll indices it is important to test their performance over a range of species (Zhang et al, 2008).…”

“…Inorder to improve the robustness and generality of chlorophyll indices it is important to test their performance over a range of species (Zhang et al, 2008). Main et al (2011) assessed the robustness of 73 published chlorophyll spectral indices using leaf level hyperspectral data collected from three crop species and a variety of savannah tree species. The authors identified two red-edge derivative based indices (red-edge position via linear extrapolation index and the modified red-edge inflection point index) that were the most consistent and robust.…”