Simultaneous measurements of corn leaf area index and mean tilt angle from multi-directional sunlit and shaded fractions using downward-looking photography

Abstract

Accurate, efficient, timely, and affordable measurements of crop structural parameters such as leaf area index (LAI) and mean tilt angle (MTA) are needed for crop growth modeling and precision field management. In this paper, a novel method was proposed to simultaneously measure corn (Zea mays L.) LAI and MTA using a low-cost indirect approach. The proposed method is based on multi-directional fractions of sunlit and shaded leaf and soil components obtained from nadir-viewing field photos captured under different solar angles. LAI and MTA were retrieved using a look-up-table (LUT) established using a Pov-Ray based geometrical canopy model. The method was validated using LAI-2200C field-measured data. Results showed that the estimated LAI were consistent with the LAI-2200C measurements, with a mean absolute error (MAE) of 0.11, relative MAE (RMAE) of 5%, and coefficient of determination (R2) of 0.89. The estimated average MTA was also close to that measured using the LAI-2200C, with the MAE of 5.9°, RMAE of 11% and R2 of 0.40. The proposed method provides accurate and efficient measurements of corn crop structural parameters. Thus, it is recommended as an affordable and effective field data collection method.