Monday, November 5, 2007
63-3

Remote Sensing for Cotton Irrigation.

Glen Lorin Ritchie1, Craig Bednarz2, James Hook1, Dana Sullivan1, and Calvin Perry1. (1) University of Georgia, P.O. Box 748, Tifton, GA 31793-0748, (2) Texas Tech University, Plant and Soil Sciences, Lubbock, TX 79409-2122

Off-the-shelf consumer digital cameras offer a convenient and user-friendly remote sensing method, if they can provide consistent remote sensing data. Two Nikon COOLPIX 4300 digital cameras were evaluated in tandem to determine the effectiveness of a cross-camera calibration procedure that would allow concurrent use of these cameras to obtain visible and near-infrared images without preset shutter speeds or aperture settings. One camera was not modified, and the other was modified to be near-infrared sensitive by replacing its internal hot mirror with a Hoya R720 filter. Each camera was calibrated at 5 exposure levels using a reflectance target consisting of 26 diffuse reflective color samples, and equations were developed that would allow exposure compensation and the conversion of brightness values to relative reflectance values. The procedure was tested on 36 cotton plots (Gossypium hirsutum) in an irrigation study during the 2006 growing season. Images obtained on 8 dates during the season using the two cameras were corrected for exposure and converted to relative reflectance values. The normalized difference vegetation index (NDVI) values from the plots were then compared with ground-based spectrometer measurements of NDVI. The corrected camera-based NDVI values were closely correlated (r2 = 0.72) with the spectrometer NDVI values, suggesting that the camera system can provide a consistent estimate of crop reflectance characteristics if exposure compensation is provided.