Evaluation of three proposed indices for the retrieval of leaf water content from the mid-wave infrared (2-6 mu m) spectra

The retrieval of leaf water content based on various indices derived from the visible to shortwave infrared (0.4–2.5 μm) has been frequently reported. The mid-wave infrared (2.5–6.0 μm) domain has surprisingly received little attention, though the main water absorption bands are located in the mid-wave infrared. This research aimed to investigate the potential of three newly proposed narrowband indices for retrieving leaf water content from the mid-wave infrared. The proposed indices were named as Mid-wave infrared Normalized Difference Water Index (MNDWI), Mid-wave infrared Simple Ratio Water Index (MSRWI) and Mid-wave infrared Simple Difference Water Index (MSDWI). Linear relations were established between the indices (calculated from all possible two-band combinations) and leaf water content. The performance of each index was evaluated based on R2 and RMSE. The proposed indices yielded high correlation with leaf water content, and among them MNDWI produced the most accurate model (R2 = 0.89 and RMSE = 7.65%) followed by MSDWI (R2 = 0.86 and RMSE = 8.66%) and MSRWI (R2 = 0.85 and RMSE = 8.86%). In conclusion, the findings of this study suggest that mid-wave infrared has the potential to retrieve leaf water content.