The dry or senescent carbon VIs provide an estimate of the amount of carbon in dry states of lignin and cellulose. Lignin is a carbon-based molecule used by plants for structural components; cellulose is primarily used in the construction of cell walls in plant tissues. Dry carbon molecules are present in large amounts in woody materials and senescent, dead, or dormant vegetation. These materials are highly flammable when dry. Increases in these materials can indicate when vegetation is undergoing senescence. See Carbon for more information. You can use these VIs for fire fuel analysis and detection of surface litter. They use reflectance measurements in the shortwave infrared range to take advantage of known absorption features of cellulose and lignin.

These indices provide suspect results in wet environments, or when the dry materials are obscured by a green canopy.

Cellulose Absorption Index (CAI)

This index indicates exposed surfaces containing dried plant material. Absorptions in the 2000 nm to 2200 nm range are sensitive to cellulose. Applications include crop residue monitoring, plant canopy senescence, fire fuel conditions in ecosystems, and grazing management.

The value of this index ranges from -3 to more than 4. The common range for green vegetation is -2 to 4. See Narrowband Definitions for the allowable range of wavelengths.

References:

Daughtry, C. "Discriminating Crop Residues from Soil by Short-Wave Infrared Reflectance." Agronomy Journal 93 (2001): 125-131.

Daughtry, C., E. Hunt Jr., and J. McMurtrey III. "Assessing Crop Residue Cover Using Shortwave Infrared Reflectance." Remote Sensing of Environment 90 (2004): 126-134.

Lignin Cellulose Absorption Index (LCAI)

This index is the sum of the relative depths of cellulose and lignin absorption features near 2100 and 2300 nm. It can be used to monitor crop residue. It was originally designed for use with ASTER bands, but it can be used with any sensor whose shortwave-infrared (SWIR) bands fall within the following ranges listed in the equation below. WorldView-3 SWIR images can be used with this index.

Reference: Daughtry, C., E. Hunt, Jr., P. Doraiswamy, and J. McMurtrey III. "Remote Sensing the Spatial Distribution of Crop Residues." Agronomy Journal 97 (2005): 864-871.

Normalized Difference Lignin Index (NDLI)

This index estimates the relative amounts of lignin contained in vegetation canopies. Reflectance at 1754 nm is largely determined by lignin concentration of leaves, as well as the overall foliage biomass of the canopy. Together, leaf lignin concentration and canopy foliar biomass are combined in the 1750 nm range to predict total canopy lignin content. Applications include ecosystem analysis and detection of surface plant litter. The NDLI is highly experimental.

See Narrowband Definitions for the allowable range of wavelengths.

If you used an atmospheric correction tool to create a surface reflectance image, they automatically scale the resulting data values by 10,000 to produce integer data that consumes less disk space. Before calculating NDLI, import the FLAASH or QUAC image into the Apply Gain and Offset tool (or the ApplyGainOffset task in the ENVI API). Set the Gain Values for all bands to 0.0001. Keep the default value of 0 for Offset Values for all bands. Save this as a new raster. The result will have reflectance values that range from 0 to 1. Because NDLI is a logarithmic function, it is especially sensitive to scale factors. Ensuring that data values range from 0 to 1 will yield the most accurate result.

References:

Serrano, L., J. Penuelas, and S. Ustin. "Remote Sensing of Nitrogen and Lignin in Mediterranean Vegetation from AVIRIS Data: Decomposing Biochemical from Structural Signals." Remote Sensing of Environment 81 (2002): 355-364.

Fourty, T., et al. "Leaf Optical Properties with Explicit Description of Its Biochemical Composition: Direct and Inverse Problems." Remote Sensing of Environment 56 (1996): 104-117.

Melillo, J., J. Aber, and J. Muratore. "Nitrogen and Lignin Control of Hardwood Leaf Litter Decomposition Dynamics." Ecology 63 (1982): 621-626.

Plant Senescence Reflectance Index (PSRI)

This index maximizes the sensitivity of the index to the ratio of bulk carotenoids (for example, alpha-carotene and beta-carotene) to chlorophyll. An increase in PSRI indicates increased canopy stress (carotenoid pigment), the onset of canopy senescence, and plant fruit ripening. Applications include vegetation health monitoring, plant physiological stress detection, and crop production and yield analysis.

The value of this index ranges from -1 to 1. The common range for green vegetation is -0.1 to 0.2. See Narrowband Definitions for the allowable range of wavelengths.

Reference: Merzlyak, J., et al. "Non-destructive Optical Detection of Pigment Changes During Leaf Senescence and Fruit Ripening." Physiologia Plantarum 106 (1999): 135-141.

See Also

Spectral Indices, Vegetation Indices, Vegetation Analysis Tools, Agricultural Stress Tool, Fire Fuel Tool, Forest Health Tool, Vegetation and Its Reflectance Properties