Remote sensing measures specific wavelengths of light that are reflected from the leaves of plants in the field.
In addition to light in the visible spectra, light in the near infrared spectrum (NIR, which is not visible with the naked eye and is reflected by the plant) is measured as well (Martin, 2004).
Larger plants with more leaves will reflect more NIR light than smaller plants, just as healthy vigorous plants of a given size will reflect more NIR light than stressed plants of the same size.
Reflectance data were measured and used to calculate NDVI, which has been found to be correlated to plant size,
vigor and yield of crops.
In this study, at different critical periods the correlation between NDVI and yield was derived.
Though variations could be observed between NDVI and yield, yet a positive correlation was obtained representing a linear relation,where lower range of NDVI that represented by 0.04–0.17 reflects the lower yield of 1.3 tonnes/acre, meanwhile the higher range of NDVI (0.43–0.57) reflects the higher yield of 3.0 tonnes/acre, Figs. 13 and 14.