Frequently Asked Questions - NDVI

FAQs - NDVI

NDVI (Normalized Difference Vegetation Index)

        Uses

  • plant vigor detection
  • differences in soil water availability
  • foliar nutrient content (when water is not limiting)
  • determining yield potential

Summary

As plants become healthier, the intensity of reflectance increases in the NIR and decreases in the Red, which is the physical basis for most vegetation indices. NDVI values can be a maximum value of 1, with lower values indicating lower plant vigor. Therefore, 0.5 typically indicates low vigor whereas 0.9 indicates very high vigor. NDVI is also effective for distinguishing vegetation from soil. NDVI is recommended when looking for differences in above-ground biomass in time or across space. NDVI is most effective at portraying variation in canopy density during early and mid development stages but tends to lose sensitivity at high levels of canopy density.

Further advanced types provided more detailed information regarding the vegatation health and many other indicators. These Include NDRE, OSAVI, CIR Composite and Chlorophyll Maps, to name a few.

There are two general types of NDVI - Relative NDVI - Calibrated NDVI.

RELATIVE NDVI is a non-numeric image classification which provides an eight color class range from Low to High.  This is an excellent product for harvest planning and problem identification, a good product for evaluating soils and stress, but only a fair product for year-to-year comparisons.  A comparison of the individual surveys is not advisable.

This index is typically generated by using a single NIR sensor or converted standard camera.

CALIBRATED NDVI (CNDVI) provides a numeric scale from 0 to 1 and can be broken into as many classes as the client desires, typically 10 or 20.  CNDVI provides a pixel by pixel data layer allowing for analysis with other biologic data, and the development of formula  which provides valuable block NDVI statistics and plant growth estimates.  This is an excellent product for indepth block analysis.

Typically this index will be generated by multi-spectral sensors which are calibrated and constantly updated in the field for actual light conditions.

 

Relative NDVI
Relative NDVI
Calibrated NDVI
Calibrated NDVI

 

False Color infrared and gray scale imagery is typically provided with these products, but is also available separately.  Change detection and leaf area indexed imagery is also available with the Calibrated NDVI.

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