Mapping of plant functional groups of subalpine and alpine grassland ecosystems using airborne imaging spectroscopy and soil-vegetation-atmosphere radiative transfer modelling

Grasslands are dominant vegetation ecosystems in subalpine and alpine areas and they are characterized by a high biodiversity (species variability and structural heterogeneity). Mapping of biodiversity is one of the key elements to study ecosystem functioning and its role in the global environment.

According to the theory of ecosystem functional diversity, plant species can be grouped into plant functional groups (PFGs), based on their functional role within the ecosystem. Plant functional groups can be identified according to easily measurable plants ?soft traits?, e.g. leaf area index, period of photosynthetic activity at canopy level, specific leaf area (SLA), dry matter content, nitrogen concentration, leaf phenology related to pigments concentration. Current advances in remote sensing technologies allow quantitative mapping of vegetation biochemical and structural properties and thus some of the canopy ?soft traits? may be estimated from remote sensing observations. The physically-based methods, retrieving vegetation properties from remote sensing data by means of canopy radiative transfer model inversion, have been successfully applied to forest and agricultural canopies; however, less attention has been paid to natural grassland ecosystems. The current challenges of ecological-based remote sensing applications are: accurate estimation of at-surface reflectance quantities from remote sensing measurements, appropriate parameterization of canopy radiative transfer models taking into account canopy architecture, and last but not least solving the inversion of canopy radiative transfer models to avoid multiple solutions. All these aspects will be covered during the research. The main objective is to identify plant functional groups of subalpine and alpine grassland ecosystems, based on canopy biochemical and structural properties estimated from airborne imaging spectroscopy data of very high spatial resolution using inversion of canopy radiative transfer models.

The research, however, will deeply focus on the following aspects:

  1. evaluation and potential use of complementary downwelling irradiance data recorded at the sensor level for estimation of at-surface reflectance quantities,
  2. optical and structural heterogeneity of subalpine and alpine grassland ecosystems in the leaf-canopy modelling domain,
  3. retrievals of selected biochemical/structural vegetation properties from airborne imaging spectroscopy data, and
  4. combination of derived biochemical and structural vegetation properties for mapping of plant functional groups in subalpine and alpine grassland ecosystems.