Comparison of Aerial Imagery from Manned and Unmanned Aircraft Platforms for Monitoring Cotton Growth

Unmanned aircraft systems (UAS) have emerged as a low-cost and versatile remote sensing platform. These systems fill a gap between ground- and manned aircraft-based platforms to provide higher resolution image data, but little work has been done to compare imagery from these two types of platforms for crop assessment. The objective of this study was to compare the images taken from manned and unmanned platforms for monitoring cotton growth. A manned aircraft equipped with a red-green-blue (RGB) camera, a modified near-infrared (NIR) camera, a thermal camera and a hyperspectral camera was used to take images at 1000 and 2000 ft from test plots on four different dates in 2016. Two multi-rotor UAS equipped with a RGB camera, a color-infrared (CIR) camera and a thermal camera along with a fixed-wing UAS equipped with a different CIR camera were used to acquire high resolution images at less than 400 ft on multiple dates. The RGB/NIR/CIR/thermal imagery taken by both manned and unmanned platforms on June 23 were used for comparison. The RGB/NIR/CIR images and the thermal images were, respectively, registered to each other between the two types of platforms. The high resolution images were then aggregated to the coarser resolution for the manned platform. Correlation matrices were calculated among all the visible and NIR bands as well as between the thermal images. The normalized difference vegetation index (NDVI) was also calculated for the images from the manned and unmanned platforms. Crop canopy cover was estimated from the images. The two types of platforms were also briefly compared in terms of image quality, ground coverage, data storage and processing, and cost-effectiveness.