Table 5.
Spectral water indices and their relationship with water relation parameters in diverse plant species and growth conditions using ground based, aircraft, and satellite spectrometers
| Water index | Parameter related | Growth conditions | Plant species | Comments | Reference |
| WI | RWC and ψleaf | Greenhouse and growth chambers | Gerbera and pepper | Ground-based spectrometer. Artificial leaf dehydration and weaker association at lower RWC <(85%) and ψleaf (–1.55 MPa) (r=0.60–0.80) | Peñuelas et al. (1993) |
| NDWI | Vegetation water content | Field and laboratory | Natural vegetation and irrigated fields | Airborne imaging spectrometer (AVIRIS). NDWI was highly related to the vegetation water content. | Gao (1996) |
| WI | Plant and seedling water content | Plastic tunnels and natural conditions | Shrubs and tree species | Ground-based spectrometer. Weaker association when plants are growing in natural conditions (r=0.05–0.75) | Peñuelas et al. (1997) |
| NDWI, SRWI, and PWI | Plant water status | Natural vegetation and farm fields | Forest and wheat | Satellite spectrometer (MODIS). Simulated models for estimating vegetation water content in relation to leaf thickness, biomass, and leaf are index | Zarco-Tejada and Ustin (2001); Zarco-Tejada et al. (2003) |
| 975, 1200, and 1750 nm for diverse ratios | RWC | Laboratory (leaves collected from trees of urban areas) | Quercus species | Ground-based spectrometer. High relationship between diverse ratios using 975, 1200, and 1750 nm wavelengths | Pu et al., 2003 |
| NDVI, SR, NDVI, and WI | Tissue water content of leaves, fruits, stems, and flowers | Natural vegetation | Annual species and perennial species (vines, shrubs, and tree species)s | Ground-based spectrometer. WI gave better results for estimating tissue water content (r2=0.51) | Sims and Gamon (2003) |
| NDWI and NDVI | Leaf and stem water content | Farm fields | Soybean and corn | Airborne imagery. Vegetation water content according to leaf area index | Anderson et al. (2004) |
| NDWI and NDVI | Leaf water content and ψleaf | Farm field | Corn and soybean | Imagery (Landsat satellite). NDWI resulted better to mapping vegetation water content (r2=0.44–0.68) | Jackson et al. (2004) |
| NDWI, NDVI, WI, and 680–780 red edge band | Plant water content | Experimental field plots | Winter wheat varieties | Ground-based spectrometer. Plant water content was better estimated using a red edge wavelengths (680–780 nm) and ψleaf were better estimated using 970 nm and NDWI (r=0.34–0.75) | Liu et al. (2004) |
| 965–1085 nm, 1192–1282 nm, and others | Leaf water content | Experimental field plots | Wheat | Ground-based spectrometer. 965–1085 nm and 1192–1282 nm gave stronger association with leaf water content | Zhao et al. (2004) |
| NDWI, NDVI, 970, and 1200 nm | Leaf water content and ψleaf | Natural vegetation | Two conifers (Pinus edulis and Juniperus monosperma) | Ground-based spectrometer. Leaf water content and ψleaf were better estimated using 970 nm and MDWI (r2=0.44–0.68) | Stimson et al. (2005) |
| NDWI and WI | RWC and ψleaf | Growth chambers | Populus spp. | Ground-based spectrometer. Excluding ψleaf of –1.6 MPa, high relationship at the leaf level using NDWI | Eitel et al. (2006) |
| WDI | Experimental field plots | Broccoli plants | Ground-based spectrometer. WDI detected differences in canopy water content | El-Shikha et al. (2007) |
NDVI, normalized difference vegetation index; NDWI, normalized difference Water index; MDWI, maximum difference water index; PWI, plant water index; SR, simple ratio; SRWI, simple ratio water index; WI, water index; WDI, water differential index.