How deep does a remote sensor sense? Expression of chlorophyll content in a maize canopy

Remote sensing offers a unique perspective of plant vigor based on reflectance of the crops' canopy. The goal of this study was to determine how deep into the maize canopy red-edge chlorophyll index, CIred edge, was affected by foliar chlorophyll (Chl) content and leaf area. Reflectance in the range 400 to 900 nm was measured at both the leaf and canopy levels and was used to determine foliar Chl and total canopy Chl content using CIred edge. Statistical techniques, a hierarchical regression and three Aikaike Information Criteria, were used to determine how many leaf layers are sensed by the CIred edge. All statistical techniques showed that the CIred edge senses the chlorophyll content of the upper 7 to 9 leaf layers in a maize canopy and that remote sensing technique is able to accurately estimate maize canopy Chl content.

► Leaf layer with maximal maize chlorophyll (Chl) located at the depth 1–1.5 m ► Red edge chlorophyll index senses Chl content in 7 to 9 leaf layers ► Remote technique accurately estimates total maize canopy Chl content