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Abstract
The spectral vegetation index (ρNIR − ρSWIR)/(ρNIR + ρSWIR), where ρNIR and ρSWIR are the near-infrared (NIR) and shortwave-infrared (SWIR) reflectances, respectively, has been widely used to indicate vegetation moisture condition. This index has multiple names in the literature, including infrared index (II), normalized difference infrared index (NDII), normalized difference water index (NDWI), normalized difference moisture index (NDMI), land surface water index (LSWI) and normalized burn ratio (NBR). After reviewing each term's definition, associated sensors and channel specifications, we found that the index consists of three variants, differing only in the SWIR region (1.2–1.3, 1.55–1.75 or 2.05–2.45 μm). Thus, three terms are sufficient to represent these three SWIR variants; other names are redundant and therefore unnecessary. Considering the spectral representativeness, the term's popularity and the ‘rule of priority’ in scientific nomenclature, NDWI, NDII and NBR, each corresponding to the three SWIR regions, are more preferable terms.
Acknowledgements
This study was funded by the National Basic Research Program of China (973 Program) under Grant No. 2009CB723906 and the US Geological Survey Climate Effects Network and Global Change Research & Development Programs and the K. C. Wong Education Foundation, Hong Kong. The work by Lei Ji was performed under USGS contract G08PC91508. We thank James Vogelmann and Michael Budde for reviewing the manuscript and providing valuable comments.