Abstract
Unmanned aerial vehicles (UAVs) combined with different spectral range sensors are an emerging technology for providing early weed maps for optimizing herbicide applications. Considering that weeds, at very early phenological stages, are similar spectrally and in appearance, three major components are relevant: spatial resolution, type of sensor and classification algorithm. Resampling is a technique to create a new version of an image with a different width and/or height in pixels, and it has been used in satellite imagery with different spatial and temporal resolutions. In this paper, the efficiency of resampled-images (RS-images) created from real UAV-images (UAV-images; the UAVs were equipped with two types of sensors, i.e., visible and visible plus near-infrared spectra) captured at different altitudes is examined to test the quality of the RS-image output. The performance of the object-based-image-analysis (OBIA) implemented for the early weed mapping using different weed thresholds was also evaluated. Our results showed that resampling accurately extracted the spectral values from high spatial resolution UAV-images at an altitude of 30 m and the RS-image data at altitudes of 60 and 100 m, was able to provide accurate weed cover and herbicide application maps compared with UAV-images from real flights.
Highlights
Site-specific weed management (SSWM) could be used as an alternative to adjust the herbicide treatment to the weed patches only and to consider different herbicide applications according to the weed species, weed group composition or weed thresholds [8,9,10,11]
An effective strategy may consist of the use of a single herbicide treatment for weed patches where a unique group of weeds are present, the use of several herbicides depending on the presence of different weed species or group compositions, or the use of a herbicide treatment based on percentage weed cover or weed threshold
Our results show that the experiment could be completed if resampling is applied to the available Unmanned aerial vehicles (UAVs) imagery acquired at lower altitudes
Summary
Even when the patchy distribution of weeds in sunflower fields, as well as the variability in the abundance and type of weeds, has been demonstrated using on-ground sampling [1,2,3], herbicides are usually broadcast over the entire field, including weed-free zones, using a unique kind of herbicide.This extensive application of herbicides has relevant economic and environmental implications, and plays a role in the development of herbicide-resistant weed biotypes [4,5,6,7].To overcome this situation, site-specific weed management (SSWM) could be used as an alternative to adjust the herbicide treatment to the weed patches only and to consider different herbicide applications according to the weed species, weed group composition (e.g., against broadleaved, grass or resistant weeds) or weed thresholds (i.e., the weed infestation cover above which a treatment is required) [8,9,10,11]. Even when the patchy distribution of weeds in sunflower fields, as well as the variability in the abundance and type of weeds, has been demonstrated using on-ground sampling [1,2,3], herbicides are usually broadcast over the entire field, including weed-free zones, using a unique kind of herbicide This extensive application of herbicides has relevant economic and environmental implications, and plays a role in the development of herbicide-resistant weed biotypes [4,5,6,7]. An effective strategy may consist of the use of a single herbicide treatment for weed patches where a unique group of weeds are present, the use of several herbicides depending on the presence of different weed species or group compositions, or the use of a herbicide treatment based on percentage weed cover or weed threshold
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