Why do NDVI readings taken at different heights above the crop canopy remain constant? And, how does the sensor integrate a 24″ wide area at different heights above the crop?
NDVI readings remain similar through the 32-48″ range because the computation is actually a normalized ratio. Even though the intensity of the light source decreases as it moves farther away from the crop canopy, the sensor proportionally adjusts and therefore, NDVI readings are not affected by height variance. Also, optical masking and position of the sensor LEDs allows the sensor to view only a 24″ wide strip regardless of the sensor height.
