arvi: Atmospherically Resistant Vegetation Index
In ASIP: Automated Satellite Image Processing

Description Usage Arguments Value Note References Examples

Atmospherically Resistant Vegetation Index (ARVI) is a vegetation based index which minimizes the effects of atmospheric scattering in comparison to NDVI.

1	arvi(directory = getwd(), crop = "n", ext2crop = "none", gamma = 1)

`directory`	Path to Satellite image folder. Assign as string (inside double quotes). Either assing inside function or set up satellite image folder as the current working directory before running the function. To define current working directory, either use shortcut key Ctrl+Shift+H or use `setwd` funtion.
`crop`	Defines the method of cropping outputs to custom extent. "n" <- No cropping required (Default). "u" <- Satellite image will be plotted in the plot window and user can choose the extent by clicking on the top left maximum followed by bottom right maximum. "y" <- Crop to the maximum and minimum extent of the shapefile. "f" <- Crop to exact shapefile boundary.
`ext2crop`	Path to the shapefile (*.shp) which will be used for cropping. Shapefile should have SAME CORDINATE SYSTEM as the satellite image. Either provide the full path of .shp file or provide the name of the shapefile variable which is already opened.
`gamma`	It is an aerosol dependant factor. For more details please refer Kaufman and Tanre (1992). By default the value is 1.

Computed ARVI product

1. ARVI = (r_nir - rb)/(r_nir + rb), where

rb = r_red - gamma (r_blue - r_red)' and "r_" denotes Top Of Atmoshpere (TOA) reflection, 'gamma' value is 1 by default as recommended if information about the aerosol type is not available. Please refer Kaufman and Tanre (1992) for more details.

Other important notes are mentioned in custom.eqn.

Kaufman, Y. J. and D. Tanre (1992) Atmospherically resistant vegetation index (ARVI) for EOS-MODIS, IEEE Transactions on Geoscience and Remote Sensing, 30 (2). doi:10.1109/36.134076.

library (raster)
library (rgdal)
# Finding the path of the sample satellite image directory.
# User may define paths directly like "/home/ur_folder" or "C:/ur_folder"
path <- system.file ("TM_sample", package = "ASIP")
shapefil <- paste0 (path, "/test.shp")
op <- arvi (directory = path, crop = "y", ext2crop = shapefil)