Water-related Spectral Reflectance Indices: Principle, Constructing, Application, and Improvement

Water related spectral reflectance indices (WIs) have been developed to characterize vegetation water content, surface water bodies, wetland, and soil water content, based on the sensitivity of different spectral bands to water in the soil, plant, and on the surface. These WIs are widely used in drought monitor, water body detection, wetland monitor, and flood hazards assessment etc. However, the selecting of appropriate WIs in specific study field is confusing because of preferences of terminology and arbitrary selection of WIs in respective applications. This review surveyed the developments and various applications of WIs in four different fields including surface water detection, vegetation water detection, soil water detection, and wetland detection. We first discussed the underlying principles and constructions (e.g., ratio and normalized difference of two bands) of different WIs based on the spectrum features of water, vegetation, and soil from our field experiments. Then we summarized different WIs terms used in similar study field to clarify the usage of WIs terms in corresponding field and reduce confusion brought by terminology. Application examples from different studies in each category were then compared to show the performances of different indices. Finally, conclusions were drawn where gaps exist and potential improvements can be made in future. The objectives of this review are to clarify the suitability of different WIs in different applications and to identify the existing gaps to facilitate future improvements.