Accurate ortho-mosaicked six-band multispectral UAV images as affected by mission planning for precision agriculture proposes

• Published in: International journal of remote sensing 2017-05, Vol.38 (8-10), p.2161-2176
• Main Authors: Mesas-Carrascosa, F. J., Clavero Rumbao, I., Torres-Sánchez, J., García-Ferrer, A., Peña, J. M., López Granados, F.
• Format: Article
• Language: English
• Subjects: Accuracy; Agricultural management; Agriculture; Altitude; Bundle adjustment; Bundling; Crops; Flight; Flight altitude; Freshwater; Ground level; Image classification; Image quality; Imagery; Land use; Military technology; Mission planning; Mosaics; Overflow; Precision farming; Resolution; Seedlings; Sensors; Spatial resolution; Spectral resolution; Unmanned aerial vehicles; Weed control; Weeds; Workflow
• ISSN: 0143-1161; 1366-5901
• DOI: 10.1080/01431161.2016.1249311

Weed mapping at very early phenological stages of crop and weed plants for site-specific weed management can be achieved by using ultra-high spatial and high spectral resolution imagery provided by multispectral sensors on-board an unmanned aerial vehicle (UAV). These UAV images cannot cover the whole field, resulting in the need to take a sequence of multiple overlapped images. Therefore, the overlapped images must be oriented and ortho-rectified to create an accurate ortho-mosaicked image of the entire field for further classification. Because the spatial quality of ortho-mosaicked images mainly depend on the flight altitude and percentage of overlap, this paper describes the effect of flight parameters using a multirotor UAV and a multispectral camera on the mosaicking workflow. The objective is to define the best configuration for the mission planning to generate accurate ortho-images. A set of flights with a range of altitudes (30, 40, 50, 60, 70, 80, and 90 m) above ground level (AGL) and two end-lap and side-lap settings (60-30% and 70-40%) were studied. The spatial accuracy of ortho-mosaics was evaluated taking into consideration the ASPRS test. The results showed that the best flight setting to keep the spatial accuracy in the bundle adjustment was 70-40% overlap and altitudes AGL ranging from 60 to 90 m. At these flight altitudes, the spatial resolution was quite similar, making it possible to optimize the mission planning, flying at a higher altitude and increasing the area overflow without decreasing the ortho-mosaic spatial quality. This study has relevant implications for further use in detecting weed seedlings in crops.