# Monitoring Safron Crops with UAVs
## 2 Related Work  
UAV technologies is a significant innovation facilitating not only the monitoring of crop production, but also the farmers themselves towards estimating the earnings from crop production. UAVs can provide information that ease the handling of problems detected in the fields and/or optimize harvesting by estimating the yield. Up until now, UAVs have been utilized in a variety of applications for Precision Agriculture, since they can affect productivity and efficiency of multiple farming processes. Such applications refer to soil analysis [1,2], mammal detection [3], and most specifically in monitoring field cultivation processes for different kinds of crops. It is a fact that weeds growing in agricultural crops are not desirable plants and can affect production significantly. Usually, they appear due to space or water, intervening with the growth of crop yields and harvesting processes. Weed management is basically focused on the utilization of herbicides. However, such spraying not only poses a heavy pollution threat to the environment, but also significantly affects the growth and yield of the crops. Due to the aforementioned issues, Site-Specific Weed Management (SSWM) with UAVs is becoming quite popular [4]. This technique manages the spatially variable application of herbicides, avoiding spraying the entire field. In particular, the field is organized and separated into different management zones, since weed plants are known to be spread through only a few spots of the field. This way, UAVs can collect multiple images from the field and then generate an accurate weed cover map for the precise spraying of herbicide according to the needs of each zone. UAVs are also popular for their ability to provide an estimation regarding the yield via monitoring the growth of vegetation. It is already proven that real-time monitoring of the cultivation process can increase the quality and quantity of agricultural productivity [5,6]. UAVs can collect variable information from the fields, flying in different heights and angles. The acquisition of images in a regular base can enable the recording of variabilities observed in the growth of crops, as well as the status of the overall biomass. UAV images can be also utilized to produce three-dimensional digital maps of the crops, providing a better view and understanding of parameters such as crop height, distance between rows or between plants, and the index Leaf Area Index (LAI). Monitoring the quantity of nitrogen content, as well as the biomass, which is the most common crop parameter, can lead to considerable conclusions regarding the need for additional fertilizer or other actions during cultivation. Based on this information, farmers can effectively and efficiently manage the use of inputs, the timing of harvesting, and the amount of soil and yield pathogens. Similarly, collecting images from UAVs can also be beneficial for the detection of diseases in crops, even at early stages [7]. Constant monitoring of the health of vegetation is proven to be of significant importance toward preventing economic loss, as well as the further spreading of the disease. Poor vegetation health will eventually lead to reduced yield and consequently to the reduction of quality of production. Pesticides is a common countermeasure for plant diseases. However, such a strategy is quite costly and also increases the likelihood of groundwater contamination as pesticide residues in the products. UAV-based data-processing technologies can enable the detection of changes in biophysical and biochemical characteristics of the crops via an automated non-destructive manner. UAV disease control can occur either at the initial stage of infection by collecting crop health relevant information, or during the treatment of infection when farmers can use UAVs for targeted spraying, as well as for accurately monitoring the course of their intervention.