SR

Summary

Calculates the Simple Ratio (SR) from a multiband raster object and returns a raster object with the index values.

Discussion

The Simple Ratio (SR) method is a common vegetation index for estimating the amount of vegetation. It is the ratio of light scattered in the NIR and absorbed in red bands, which reduces the effects of atmosphere and topography.

Values are high for vegetation with a large leaf area index, or high canopy closure, and low for soil, water, and nonvegetated features. The range of values is from 0 to approximately 30, where healthy vegetation generally falls between values of 2 and 8.

SR = NIR / Red

For information about other multiband raster indexes, see the Band Arithmetic raster function.

The referenced raster dataset for the raster object is temporary. To make it permanent, you can call the raster object's save method.

Syntax

SR (raster, {nir_band_id}, {red_band_id})

Parameter	Explanation	Data Type
raster	The input raster.	Raster
nir_band_id	The band ID of the near-infrared band. The ID index uses one-based indexing. (The default value is 5)	Integer
red_band_id	The band ID of the red band. The ID index uses one-based indexing. (The default value is 4)	Integer

Return Value

Data Type	Explanation
Raster	The output raster with SR values.

Code sample

SR example

Calculates the Simple Ratio for a multispectral image.

import arcpy

SR_raster = arcpy.ia.SR("MSimage.tif",5,4)