Abstract
Accurate mapping of weed distribution within a field is a first step towards effective weed management. The aim of this work was to improve the mapping of milk thistle (Silybum marianum) weed patches through unmanned aerial vehicle (UAV) images using auxiliary layers of information, such as spatial texture and estimated vegetation height from the UAV digital surface model. UAV multispectral images acquired in the visible and near-infrared parts of the spectrum were used as the main source of data, together with texture that was estimated for the image bands using a local variance filter. The digital surface model was created from structure from motion algorithms using the UAV image stereopairs. From this layer, the terrain elevation was estimated using a focal minimum filter followed by a low-pass filter. The plant height was computed by subtracting the terrain elevation from the digital surface model. Three classification algorithms (maximum likelihood, minimum distance and an object-based image classifier) were used to identify S. marianum from other vegetation using various combinations of inputs: image bands, texture and plant height. The resulting weed distribution maps were evaluated for their accuracy using field-surveyed data. Both texture and plant height have helped improve the accuracy of classification of S. marianum weed, increasing the overall accuracy of classification from 70% to 87% in 2015, and from 82% to 95% in 2016. Thus, as texture is easier to compute than plant height from a digital surface model, it may be preferable to be used in future weed mapping applications.
Highlights
Understanding and limiting the damage that can be caused by weeds to a crop, either within the current or upcoming growing season, is central to the effective overall management of the crop.The most common way of treating weeds is the application of herbicides, but this method exposes both the consumers and the environment to potential risks
The aim of this work was to demonstrate the improvement of accuracy of S. marianum weed mapping through unmanned aerial vehicle (UAV) images with the use of auxiliary layers of information, such as spatial texture and estimated vegetation height from a UAV digital surface model
After applying the three classification algorithms on various combinations of input data layers, nine maps with the distribution of S. marianum weeds were produced for each year (Figures 5 and 6)
Summary
Understanding and limiting the damage that can be caused by weeds to a crop, either within the current or upcoming growing season, is central to the effective overall management of the crop. The most common way of treating weeds is the application of herbicides, but this method exposes both the consumers and the environment to potential risks. Silybum marianum or milk thistle is a weed akin to the common thistle. It belongs to the Asteraceae family and can be either an annual or biennial plant. It has a characteristic purple-coloured flower, while its leaves are green with white veins.
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