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

The retrieval of leaf water content based on various indices derived from the visible to shortwave infrared (0.4-2.5 mu m) has been frequently reported. The mid-wave infrared (2.5-6.0 mu m) 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 R-2 and RMSE. The proposed indices yielded high correlation with leaf water content, and among them MNDWI produced the most accurate model (R-2 = 0.89 and RMSE = 7.65%) followed by MSDWI (R-2= 0.86 and RMSE = 8.66%) and MSRWI (R-2= 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. (C) 2012 Elsevier B.V. All rights reserved.