Retrieval of Hyperspectral Information from Multispectral Data for Perennial Ryegrass Biomass Estimation

Abstract

The use of spectral data is seen as a fast and non-destructive method capable of monitoring pasture biomass. Although there is great potential in this technique, both end users and sensor manufacturers are uncertain about the necessary sensor specifications and achievable accuracies in an operational scenario. This study presents a straightforward parametric method able to accurately retrieve the hyperspectral signature of perennial ryegrass (Lolium perenne) canopies from multispectral data collected within a two-year period in Australia and the Netherlands. The retrieved hyperspectral data were employed to generate optimal indices and continuum-removed spectral features available in the scientific literature. For performance comparison, both these simulated features and a set of currently employed vegetation indices, derived from the original band values, were used as inputs in a random forest algorithm and accuracies of both methods were compared. Our results have shown that both sets of features present similar accuracies (root mean square error (RMSE) ≈490 and 620 kg DM/ha) when assessed in cross-validation and spatial cross-validation, respectively. These results suggest that for pasture biomass retrieval solely from top-of-canopy reflectance (ranging from 550 to 790 nm), better performing methods do not rely on the use of hyperspectral or, yet, in a larger number of bands than those already available in current sensors.

Within and combined season prediction models for perennial ryegrass biomass yield using ground- and air-based sensor data

“…Since plant height is easy to measure and extract from inexpensive sensors/cameras, the current trend of developing prediction models is based on the combination of plant height with other parameters (like VIs). While the VIs remain the fixed limitation, the main improvement of model accuracy is therefore depended on the plant height capacity (Togeiro de Alckmin et al, 2021). Many studies showed that higher accuracy of plant height was measured by being closer to the ground level than aerial cameras (Madec et al, 2017;Wang et al, 2018;Yuan et al, 2018a).…”