The light use efficiency VIs provide a measure of the efficiency with which vegetation can use incident light for photosynthesis. Light use efficiency is highly related to carbon uptake efficiency and vegetative growth rates, and is somewhat related to fractional absorption of photosynthetically active radiation (fAPAR). These VIs help to estimate growth rate and production, which is useful in precision agriculture. These VIs use reflectance measurements in the visible spectrum to take advantage of relationships between different pigment types to assess the overall light use efficiency of the vegetation.

Photochemical Reflectance Index (PRI)

This index is a reflectance measurement that is sensitive to changes in carotenoid pigments (particularly xanthophyll pigments) in live foliage. Carotenoid pigments are indicative of photosynthetic light use efficiency, or the rate of carbon dioxide uptake by foliage per unit energy absorbed. As such, it is used in studies of vegetation productivity and stress. Applications include vegetation health in evergreen shrublands, forests, and agricultural crops prior to senescence.

The value of this index ranges from -1 to 1. The common range for green vegetation is -0.2 to 0.2. See Narrowband Definitions for the allowable range of wavelengths.

References: Penuelas, J., I. Filella, and J. Gamon. "Assessment of photosynthetic radiation-use efficiency with spectral reflectance." New Phytologist 131 (1995): 291-296.

Gamon, J., L. Serrano, and J. Surfus. "The Photochemical Reflectance Index: An Optical Indicator of Photosynthetic Radiation Use Efficiency Across Species, Functional Types and Nutrient Levels." Oecologia 112 (1997): 492-501.

Structure Insensitive Pigment Index (SIPI)

This index is a reflectance measurement designed to maximize the sensitivity of the index to the ratio of bulk carotenoids (for example, alpha-carotene and beta-carotene) to chlorophyll while decreasing sensitivity to variation in canopy structure (for example, leaf area index). Increases in SIPI are thought to indicate increased canopy stress (carotenoid pigment). Applications include vegetation health monitoring, plant physiological stress detection, and crop production and yield analysis. SIPI is defined by the following equation:

The value of this index ranges from 0 to 2. The common range for green vegetation is 0.8 to 1.8. See Narrowband Definitions for the allowable range of wavelengths.

Reference: Penuelas, J., F. Baret, and I. Filella. "Semi-Empirical Indices to Assess Carotenoids/Chlorophyll-a Ratio from Leaf Spectral Reflectance. " Photosynthetica 31 (1995): 221-230.

Structure Independent Pigment Index (SIPI1)

SIPI1 is defined by the following equation:

Reference: Penuelas, J., F. Baret, and I. Filella. "Semi-Empirical Indices to Assess Carotenoids/Chlorophyll-a Ratio from Leaf Spectral Reflectance. " Photosynthetica 31 (1995): 221-230.

Red Green Ratio Index (RGRI)

This index is a reflectance measurement that indicates the relative expression of leaf redness caused by anthocyanin to that of chlorophyll. The Red Green Ratio has been used to estimate the course of foliage development in canopies. It is an indicator of leaf production and stress, and it may also indicate flowering in some canopies.

Applications include plant growth cycle (phenology) studies, canopy stress detection, and crop yield prediction. Results are reported as the mean of all bands in the red range divided by the mean of all bands in the green range.

The value of this index ranges from 0.1 to more than 8. The common range for green vegetation is 0.7 to 3. See Narrowband Definitions for the allowable range of wavelengths.

Reference: Gamon, J., and J. Surfus. "Assessing Leaf Pigment Content and Activity With a Reflectometer." New Phytologist 143 (1999): 105-117.

See Also

Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Vegetation and Its Reflectance Properties