Comparative exploration of continuum-removed absorption features from spaceborne EnMAP HSI and ground-based spectroscopy for characterizing senescent grass quality across different velds

This study evaluated whether data from the space‑borne Environmental Mapping and Analysis Programme Hyperspectral Imager (EnMAP HSI) can derive continuum-removed absorption features comparable to those from an Analytical Spectral Device (ASD) field spectroscopy for characterizing grass canopy nitrogen (N), acid detergent fibre (ADF), and acid detergent lignin (ADL) in senescent sour and sweet veld types. The results showed that the two sensors exhibited similar and well-known absorption wavelengths of senescent foliar biochemical concentrations occurring within the R550–742, R1685–1749, and R2238–2370 regions, using the continuum-removed spectra. In addition, EnMAP HSI produced the most distinct absorption curves for all the senescent grass-quality constituents in the visible region (R550–742) compared to the ASD spectrometer. The HSI sensor also produced absorption troughs in the short-wave infrared region (SWIR) that were comparable to the spectroradiometer. An independent-samples t-test was conducted to explore whether there were statistically significant differences between the senescent N, ADF, and ADL continuum-removed spectra derived from EnMAP HSI and ASD spectroradiometer. Results showed that the continuum-removed spectra from these sensors showed statistically significant differences (padj < 0.05) in the R550–742 in both velds and exhibited insignificant differences (padj ˃ 0.05) in the SWIR wavelength ranges (R1116–1284, R1685–1749, R2032–2208, and R2238–2370) across all variables. EnMAP HSI produces continuum-removed absorption features that are broadly comparable to ASD measurements, demonstrating their reliability for regional grassland biochemical assessment. The availability of freely available EnMAP data reduces data dependence on labour-intensive, spatially limited field spectroscopy, and enables more scalable monitoring of forage quality across landscapes. This study provides a foundation for further research on using satellite-derived absorption features and continuum removal for estimating senescent grass biochemicals.