UV-Vis-NIR Leaf Reflectance Spectroscopy with Pine needle and Small Leaf Adapter

With the growing influence of climate change, it is critical to have effective tools to monitor environmental health. Climate change and land use change are affecting ecosystems drastically, and vegetation is often the first to show symptoms. Stress factors can come in the form of invasive species, reduced water availability, and land use change.

Increasing economic activity, growing populations, and changes in temperature and precipitation regimes pose major threats to freshwater ecosystems and biodiversity in many catchments (Ramoelo et al., 2014). Climate change will compound the threat of alien plants on water resources, and it is predicted to accelerate the rate of invasive plant spread. Remote sensing using a small leaf adapter can give a robust analysis of the overall health of plants by analyzing indices like NDWI, leaf water potential, leaf nitrogen, moisture stress index, and many more.

The small leaf adapter, combined with Spectral Evolution’s unique Leaf-clip Reflectance Probe and the high sensitivity of the NaturaSpec™ UV-Vis-NIR spectroradiometer, allows researchers to measure precise reflectance data over the spectral range of 350nm to 2500nm.

Here we demonstrate the spectral differences in small leaf samples, including three species of pine needle and a small leaf. Measurements were taken bundled and compared to the small leaf adapter. With a regular leaf clip, typically, a sample will be taken with the needles or small leaves bunched up in the field of view. Arranging mats or needle holders, in turn, enhances mutual shading of adjacent needles, multiple scattering, or re-absorption (Rajewicz et al. 2019).

These tests yielded excellent results, showing the ability of the small leaf adapter to collect accurate leaf spectra. This was shown by the similarities between spectral shapes in Figure 1, showing that the single needle reflectance is of the same quality as the bundled spectra.

In Figure 2, there are differences between the singular needle and the bundle, primarily at the water absorption features near 1425nm and 1925nm. This shows the ability to capture the difference between the average of several needles compared to the singular leaf. In this example, the needle was less hydrated than the bundle.

In Figure 3, we demonstrate the resolution difference between the standard resolution RS-3500 and the high-resolution Naturaspec™. The RS-3500 is comparable to industry standards. The Naturaspec™ has high resolution and sensitivity. This is shown in Figure 3, where the RS-3500 begins to show noise in the single needle measurements due to the significantly lower reflectance signal of a single needle.

Figure 4 demonstrates the new ability to differentiate between different parts of an individual leaf, like the top and bottom leaf spectra, which show the ability to be very targeted even on a small leaf.

Spectral Evolution’s UV-Vis-NIR field-portable spectroradiometers are rugged and offer the best combination of high resolution and high sensitivity resulting in the most precise spectral data from any field instrument available on the market. The wide variety of accessories & fore optics makes our instruments the most versatile spectroradiometers for all types of measurements, including reflectance, radiance, irradiance, & transmittance.

References

Dzikiti, S., Schachtschneider, K., Naiken, V., Gush, M., Le Maitre, D., 2013. Comparison of water-use by alien invasive pine trees growing in riparian and non-riparian zones in the Western Cape Province, South Africa. Forest Ecology and Management 293, 92–102. https://doi.org/10.1016/j.foreco.2013.01.003

Ramoelo, A., Dzikiti, S., van Deventer, H., Maherry, A., Cho, M.A., Gush, M., 2015. Potential to monitor plant stress using remote sensing tools. Journal of Arid Environments 113, 134–144. https://doi.org/10.1016/j.jaridenv.2014.09.003