|Sudduth, Kenneth - Ken|
Submitted to: Congresso Brasileiro de Engenharia Agricola
Publication Type: Proceedings
Publication Acceptance Date: 8/2/2002
Publication Date: 8/2/2002
Citation: Souza, E.G., Scharf, P.C., Sudduth, K.A. 2002. Understanding the behavior of corn (zea mays i.) reflectance and vegetation indices as a function of sun position and clouds. Congresso Brasileiro de Engenharia Agricola.
Technical Abstract: A sensor-based, real-time variable-rate application system for N fertilizer has the potential to reduce input costs, improve yields, and reduce N loss to the environment. Past studies used data collected around solar noon with clear skies. However, for practical application, the system must work under cloudy skies or away from solar noon. The reflectance characteristics of canopies/plants under these conditions are not well known. Our objective for this project was to improve spectral radiometer reflectance corrections for variations in incoming sunlight so that the same reflectance reading will be obtained (and the same N recommendation made) for the same plants regardless of time of day or cloud conditions. Spectral radiometers were mounted in a stationary position about 25 cm above the corn canopy. Readings were taken from morning until night over several days with a range of sky conditions (sunny, overcast, partly cloudy). Experiments were done on corn ranging from V6 to V12 growth stages. Mathematical functions were developed that could represent 58% of the effects of changing sun angle and cloud conditions.