Identification and characteristic analysis of urban vegetation spectra

Identification and characteristic analysis of urban vegetation spectra under different dust deposition

In recent years, the ecological environment of cities has suffered a lot from damages due to the acceleration of urbanization. The transportation network, traffic flow, industrial activities, and the use of fossil fuels are sources of serious particulate pollutants in the urban greening environment. People pay more and more attention to dust pollution. Dust deposition capacity of plants, that is, the amount of dust deposited within unit time and unit leaf area, can reflect air quality status and can be used as an index to characterize air pollution. Many scholars have researched the dust deposition capacity of plants, which promoted the relevant research on spectral characteristics. More and more scholars combined hyperspectral remote sensing technology to study the effect of dust deposition on plant spectra.

To confirm the impact of plant dust deposition capacity on urban atmosphere and spectral characteristics, the scientists from School of Environmental and Geographical Sciences, Shanghai Normal University carried out experiments in Xuhui District and Minhang District of Shanghai, and they selected 4 common greening species as research objects. In order to explore the changes in vegetation spectral characteristics, they measured the spectral data (ASD FieldSpec 3 Spectrometer) and dust data of samples.

Study area and sample locations.

Results:

Leaf reflectance spectra curves under different dust deposition levels.

Canopy reflectance spectra curves under different dust deposition levels.

Conclusions: It can be concluded that dust deposition had great influence on the spectral characteristics of different tree species. 380-680 nm and 750-1350 nm are the best wavelength ranges for analyzing the interference of dust deposition on spectrum, and subsequent spectral studies can be carried out on the basis of this range. For the four tree species, the greater the amount of dust is, the lower the canopy reflectance can be. The spectral curve changes most obviously at 750-1350 nm. The leaf spectrum of Osmanthus fragrans is relatively undisturbed by dust, indicating that dust deposition has little effect on the growth of Osmanthus fragrans. Osmanthus fragrans is one of the shrub species that can be considered for urban dust management. The first derivative and the second derivative are important parameters for observing the influence of dust deposition on the judgment of the red edge position. The change in the slope of the spectral curve at the red edge position is also amplified, and it is found that the red edge position is prone to move under the interference of dust. The direction and size of the movement depend on the tree species and the amount of dust deposition. These conclusions will be helpful to provide a foundation for a series of dust deposition research based on the hyperspectral reflectance spectrum, such as dust estimation in the whole city. In the future, the study of plant spectrum and its dust deposition effect in the visible and near-infrared bands can also be further developed.