Practical methods for aerial image acquisition and reflectance conversion using consumer-grade cameras on manned and unmanned aircraft

Authors: Yang, Chenghai; Fritz, Bradley - Brad; Suh, Charles

Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2024
Publication Date: 5/9/2024
Citation: Yang, C., Fritz, B.K., Suh, C.P. 2024. Practical methods for aerial image acquisition and reflectance conversion using consumer-grade cameras on manned and unmanned aircraft. Precision Agriculture. https://doi.org/10.1007/s11119-024-10145-w.
DOI: https://doi.org/10.1007/s11119-024-10145-w

Interpretive Summary: Consumer-grade cameras have emerged as a cost-effective alternative to conventional scientific cameras in precision agriculture applications, yet there is a lack of information on their appropriate use. This study addressed this gap by developing practical methodologies for determining optimal camera settings and converting raw images into meaningful reflectance data for image analysis. Using two Nikon D7100 and two Nikon D850 cameras on both manned and unmanned aircraft, this study developed a practical approach that considered flight parameters to optimize camera settings for capturing high-quality images. Regression analysis involving multiple models showed that the exponential model with vertical translation was the optimal model for accurately converting raw images to reflectance data. Further model error analysis led to the selection of appropriate reflectance tarps for accurate image calibration. These findings provide practical guidance for effectively configuring consumer-grade cameras while ensuring accurate reflectance conversion for research and commercial applications in precision agriculture.

Technical Abstract: Consumer-grade cameras have emerged as a cost-effective alternative to conventional scientific cameras in precision agriculture applications, yet there is a lack of information on their appropriate use. This study focused on developing practical methodologies for determining optimal camera settings and converting image digital numbers (DNs) to reflectance. Two Nikon D7100 and two Nikon D850 cameras with visible and near-infrared sensitivity were deployed on both manned and unmanned aircraft for image acquisition. To optimize camera settings, including exposure time and aperture, an approach that considered flight parameters and image histograms was employed. Linear and nonlinear regression analyses based on multiple nonlinear models were performed to accurately characterize the reflectance-DN relationship across all four bands based on seven calibration tarps. The results revealed that the exponential model with vertical translation was the optimal model for reflectance conversion for both camera types. Based on the optimized camera parameters and the optimal model type, this study provided an extensive analysis of the models and their root mean square errors (RMSEs) derived from all 952 possible 2-, 3-, 4-, 5- and 6-tarp combinations for all bands in both camera types. This analysis led to the selection of optimal tarp combinations based on the desired level of accuracy for each of the five multi-tarp configurations. As the number of tarps increased to 4, 5, or 6, the RMSE values stabilized for all bands, indicating 4-tarp combinations were the optimal choice. These findings hold significant practical implications for practitioners in precision agriculture seeking guidance for configuring consumer-grade cameras effectively while ensuring accurate reflectance conversion.