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What is NDVI?
Different wavelengths of light are either absorbed or
reflected from plants. The amount of Chlorophyll in a plant
determines its green color. That, coupled with the leaf area
or “BioMass” in a given area, determines the intensity of
reflectance that can be measured by a sensor in certain
wavelengths: specifically the Yellow wavelength (VIS) and
the Near Infrared wavelength (NIR). The Crop Circle Sensor
emits its own light source and records the reflectance in
these two wavelengths.
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There are many Vegetation Indexes, but the industry standard
for turf is NDVI, or Normalized Difference Vegetative
Index. NDVI is simply a mathematical method of
representing the two wavelengths’ reflectance intensities in
a way that can best show differences between healthy turf
and poor growth. |
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Specifically it is: (NIR-VIS)/(NIR+VIS). The number range is
usually between .25000 and .85000. The lower range
represents a low BioMass/Chlorophyll level and the higher
Range represents a high BioMass/Chlorophyll level (a healthy
turf).
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What is the procedure?
During The Sweep™, The Crop
Circle sensor is
mounted to a mower and records reflectance once per
second. This number is attached to a distinct GPS Lat/Long
position. These points are then interpolated by Krigling to
determine an average by area (5 ft square on greens,
teeboxes, and aprons on 15 ft square on fairways and primary
roughs) and broken into 7 classes divided by a Quantile
methodology.
Each distinct area of the golf course (green, primary rough,
teebox, fairway, and apron (approach) is compared to the
others of that type so that the superintendent can determine
the differences between “Like” areas: Fairway on 17th Hole
vs. Fairway on 3rd Hole. This affords him a mechanism to
identify and prioritize his treatment resources.
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