To determine the density of green on a patch of land, researchers must observe the distinct colors (wavelengths) of visible and near-infrared sunlight reflected by the plants. As can be seen through a prism, many different wavelengths make up the spectrum of sunlight. When sunlight strikes objects, certain wavelengths of this spectrum are absorbed and other wavelengths are reflected. The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 micrometers [µm]) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 micrometers [µm]). The more leaves a plant has, the more these wavelengths of light are affected, respectively.

 

NIR

 

Vegetation reflects very well in the near infrared part of the light spectrum. NIR Vigor only uses the near infrared waveband. It tends to give the most detail of variability within the field by looking at vegetation densities of the crop and the soils environment.  Use the NIR analysis to determine the Management Zone Variability maps.   During peak vegetation periods NIR also can cut through heavy vegetation canopies and can determine variability better than an index. 

 

In Landscout the NIR button can be used on the panchromatic images to create a coloured version of the image. This is not an NIR analysis if used in this context, merely a way of forcing a colour ramp on the black and white image for easy visibility and to accentuate light reflectance

 

NDVI

 

NDVI gives a measure of only vegetative cover on the land surface over field areas. The visible channels give you some degree of atmospheric correction. The value is then normalized to partially account for differences in illumination and surface slope.  Dense vegetation shows up very strongly in the imagery, and areas with little or no vegetation are also clearly identified.

 

If there is much more reflected radiation in near-infrared wavelengths than in visible wavelengths, then the vegetation in that pixel is likely to be dense and may be the result of a more highly productive soil region. If there is very little difference in the intensity of visible and near-infrared wavelengths reflected, then the vegetation is probably sparse and may consist of areas of poor soils, low fertility, topography changes or insect or diseased areas.  In most climates, vegetation growth is limited by water so the relative density of vegetation is a good indicator of moisture availability.

 

The Normalized Difference Vegetation Index (NDVI) is a measure of the amount and vigor of vegetation at the surface. The magnitude of NDVI -R is related to the level of photosynthetic activity in the observed vegetation. In general, higher values of NDVI indicate greater vigor and amounts of vegetation.

 

NDVI is calculated from the visible and near-infrared light reflected by vegetation. Healthy vegetation absorbs most of the visible light that hits it, and reflects a large portion of the near-infrared light. Unhealthy or sparse vegetation reflects more visible light and less near-infrared light.

 

Nearly all satellite Vegetation Indices employ this difference formula to quantify the density of plant growth:
        — near-infrared radiation minus visible radiation divided by
        near-infrared radiation plus visible radiation.

You can create an NDVI Index with the Red channel or a NDVI index with the Green channel

 

NDVI - R = (NIR — VIS Red) / (NIR + VIS Red)

NDVI - G = (NIR — VIS Green) / (NIR + VIS Green)

 

NDVI Red is derived from the contrasting reflection by vegetation of radiation in the visible red and near infrared wavebands.  Atmospheric & Soil influences are subtracted from the image to provide more accurate vegetation analysis.  Use NDVI Red to determine Vegetation changes from date to date throughout the growing season or just to see the vegetation amounts at any given date.

 

NDVI Green is derived from the near infrared and visible green wavebands. Using the green channel helps determine nitrogen influences from the green color of the leaf.

Use NDVI Green for determining more accurate nitrogen deficiencies for Variable rate application of nitrogen products or to se a more direct relationship with Yield monitors.  Research from University of Nebraska (Sheppers)

 

NDVI also provides an estimate of vegetation health and a means of monitoring changes in vegetation over time. If you want to compare multiple dates of imagery throughout the season make sure you use the same NDVI  index to compare them for changes.