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Title: Acquisition of Digital Color-Infrared Photographs for Monitoring Leaf Area Index of Winter Wheat

Author
item Hunt Jr, Earle
item Hively, Wells - Dean
item LINDEN, DAVID - AERO VIEW INTERNATIONAL
item Daughtry, Craig
item McCarty, Gregory

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2010
Publication Date: 1/11/2010
Citation: Hunt, E.R., Hively, W.D., Linden, D.S., Daughtry, C.S., McCarty, G.W. 2010. Acquisition of digital color-infrared photographs for monitoring leaf area index of winter wheat. Agronomy Journal. 2:290-305.

Interpretive Summary: Aerial color-infrared photography has the high spatial resolution required for assessing within-field variability of crop growth. However, current color-infrared cameras and manned aircraft flights are expensive so the objective of this research is to determine alternative methods for obtaining remote sensing images. We describe a new method for acquiring digital color-infrared photographs for monitoring vegetation from Unmanned Airborne Vehicles (UAVs). A red-light blocking filter is placed in front of the lens of a 12-megapixel digital camera which does not have an internal filter that blocks near-infrared (NIR) light. The result is that camera that acquires photographs with NIR, green, and blue bands. We tested the capacity of the photography by assessing variations of leaf area index in winter wheat. UAVs with color-infrared cameras could provide low-cost imagery for within-season crop management because of high spatial resolution, ability to acquire imagery at critical times, and rapid delivery of information to the user.

Technical Abstract: Aerial color-infrared photography has the high spatial resolution required for assessing within-field variability of crop growth. We describe a new method for acquiring digital color-infrared photographs for monitoring vegetation on the ground or from Unmanned Airborne Vehicles (UAVs). A red-blocking filter is placed in front of the lens of a 12-megapixel digital camera that does not have an internal filter blocking near-infrared (NIR) light. The result is camera that acquires photographs with NIR, green, and blue bands. Because of differences in solar irradiance and camera-exposure settings, the NIR-green-blue digital numbers are used to compute the green normalized difference vegetation index (GNDVI). GNDVI calculated from digital numbers was linearly related to GNDVI determined from the spectral reflectances of colored tarpaulins. Winter wheat was planted on two dates and fertilized in fall and spring to obtain a large range in leaf area index (LAI). GNDVI was linearly related to LAI below 2.5 m2 m-2 with an R2 of 0.85. UAVs with color-infrared cameras could provide low-cost imagery for within-season crop management because of high spatial resolution, ability to acquire imagery at critical times, and rapid delivery of information to the user.