Center for Spatial Information Science and Systems (CSISS)
CSISS Geospatial Web Services index

Raster_NDVIService

This service is used to calculate a Normalized Difference Vegetation Index (NDVI).

NDVI is a standardized index allowing you to generate an image displaying greenness (relative biomass). This index takes advantage of the contrast of the characteristics of two bands from a multispectral raster dataset¡ªthe chlorophyll pigment absorptions in the red band and the high reflectivity of plant materials in the near infrared band.
An NDVI is often used worldwide to monitor drought, to monitor and predict agricultural production, to assist in predicting hazardous fire zones, and to map desert encroachment. The NDVI is preferred for global vegetation monitoring because it helps to compensate for changing illumination conditions, surface slope, aspect, and other extraneous factors (Lillesand 2004).
The NDVI transformation is computed as the ratio of the measured intensities in the red (R) and near infrared (NIR) spectral bands using the following formula: 
NDVI = (NIR - red) / (NIR + red)
The Advanced Very High Resolution Radiometer (AVHRR) is a 5 channel radiometer with channels in the red (channel 1) and near infrared (channel 2) potion of the spectrum. The AVHRR NDVI product is created using data from these channels in the following manner:

(AVHRR) NDVI = (channel 2 - channel 1) / (channel 2 + channel 1)
The Thematic Mapper (TM and Enhanced Thematic Mapper Plus (ETM+) bands 3 and 4) provide R and NIR measurements and therefore can be used to generate NDVI data sets with the following formula:

(ETM+) NDVI = (Band 4 - Band 3) / (Band 4 + Band 3)

Operation:

ndvi - Allows the user to calculate a Normalized Difference Vegetation Index (NDVI).

Request Parameters:

nirImageURL
URL of near infrared component of a raster map
Default format: GeoTIFF
redImageURL
URL of red component of a raster map
Default format: GeoTIFF
outputGeoTiffType
Type of output GeoTIFF file. The output Format Type is specified as GeoTIFF
Parameter format: string
Options: Byte, Int16, UInt16, UInt32, Int32, Float32, Float64, CInt16, CInt32, CFloat32, CFloat64

Response Parameters:

returnURL
URL of output raster map containing the NDVI values
returnFormat
Format of output raster map
Default: GeoTIFF

For further informations

ServiceLocation
WSDL
JavaInterface

See GRASS command

r.mapcalc

See also

http://chesapeake.towson.edu/data/all_ndvi.asp
http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Using_the_NDVI_process
http://eoweb.dlr.de:8080/short_guide/D-NDVI.html


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