Evaluation of Hybrid Models to Estimate Chlorophyll and Nitrogen Content of Maize Crops in the Framework of the Future CHIME Mission

In the next few years, the new Copernicus Hyperspectral Imaging Mission (CHIME) is foreseen to be launched by the European Space Agency (ESA). This mission will provide an unprecedented amount of hyperspectral data, enabling new research possibilities within several fields of natural resources, including the agriculture and food security domain. In order to efficiently exploit this upcoming hyperspectral data stream, new processing methods and techniques need to be studied and implemented. In this work, the hybrid approach (HYB) and its variant, featuring sampling dimensionality reduction through active learning heuristics (HAL), were applied to CHIME-like data to evaluate the retrieval of crop traits, such as chlorophyll and nitrogen content at both leaf (LCC and LNC) and canopy level (CCC and CNC). The results showed that HYB was able to provide reliable estimations at canopy level (R-2 = 0.79, RMSE = 0.38 g m(-2) for CCC and R-2 = 0.84, RMSE = 1.10 g m(-2) for CNC) but failed at leaf level. The HAL approach improved retrieval accuracy at canopy level (best metric: R-2 = 0.88 and RMSE = 0.21 g m(-2) for CCC; R-2 = 0.93 and RMSE = 0.71 g m(-2) for CNC), providing good results also at leaf level (best metrics: R-2 = 0.72 and RMSE = 3.31 mu g cm(-2) for LCC; R-2 = 0.56 and RMSE = 0.02 mg cm-2 for LNC). The promising results obtained through the hybrid approach support the feasibility of an operational retrieval of chlorophyll and nitrogen content, e.g., in the framework of the future CHIME mission. However, further efforts are required to investigate the approach across different years, sites and crop types in order to improve its transferability to other contexts.

Automated summary

The European Space Agency (ESA) is planning to launch the Copernicus Hyperspectral Imaging Mission (CHIME) in the next few years, which will provide a large amount of hyperspectral data for research in various fields including agriculture and food security. This study applied the hybrid approach (HYB) and its variant (HAL) to evaluate the retrieval of crop traits using CHIME-like data. The results showed that HYB was reliable at canopy level but failed at leaf level, while HAL improved retrieval accuracy at both levels. The promising results support the feasibility of operational retrieval of chlorophyll and nitrogen content in the future CHIME mission.