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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #133829

Title: HOW CORN REFLECTANCE AND VEGETATION INDICES ARE INFLUENCED BY SUN POSITION AND ATMOSPHERIC CONDITIONS

Author
item SOUZA, E
item SCHARF, P
item Sudduth, Kenneth - Ken

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 4/13/2002
Publication Date: 4/13/2002
Citation: SOUZA, E.G., SCHARF, P., SUDDUTH, K.A. HOW CORN REFLECTANCE AND VEGETATION INDICES ARE INFLUENCED BY SUN POSITION AND ATMOSPHERIC CONDITIONS. AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS MEETINGS PAPERS. 2002. MID-CENTRAL CONFERENCE PAPER MC02-06.

Interpretive Summary:

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 ten inches 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 in the V6 to V12 growth stages. Results showed that measured reflectance was dependent on sun angle. Vegetation indices based on red and near infrared (NIR) data were correlated with sun angle; however, vegetation indices using green and NIR data were not. Thus, sun angle effects could be minimized through the use of green/NIR vegetation indices.