## 1 Introduction
For this reason, UAVs have been mainly employed for image surveys: for example, mapping invasive weed outbreaks in coffee plantations, finding irregularities in the fertilization delivery system and determining ripeness analysis [15,16]. UAVs have also been employed in vineyard experiments with the purpose of analyzing variable soils, pest problems, differences in fruit maturity [17], and monitoring nighttime temperatures for frost mitigation [18]. Other authors have presented the development of a remote-sensing aerial platform for general mapping purposes [19]. 3D- GIS map generation employingUAVs have also been discussed in [20, 21]. Furthermore, cooperative remote sensing for real-time water management and irrigation control with small UAV is proposed in [22]. Regarding the PA concept, modern viticulture can be considered as a special type of PA. In fact Precision Viticulture (PV) deals with the existence of variability in grape yield and quality. This variability mainly depends on climate and soil properties. However soil moisture, pest and environmental diseases can also have strong impact. Agricultural practices can influence grape quality, so it is important that these applications are chosen based on site-specific conditions with the support of fine scale information. PV represents a management strategy based on fine scale information that can be used to influence the quality of wine production. Quality is perhaps one of the most important factors that affects viticulture in terms of crop value but there is generally a trade-off between them [23]. Focusing on the application of sensor networks for vineyards, similar objectives as those mentioned above for other crop can be found [24-26]. Differences come from the distribution of the sensors, the acquisition frequency, and the meaning of the data acquired. For example, vineyards are quite delicate when facing low temperature. Real-time temperature monitoring combined with historical data prediction could prevent frost effects. The analysis of moisture patterns also provides an effective way to avoid some crop pathogens, such as powdery mildew. As [27] shows, vineyards are commonly parceled into several remote and isolated small tracts of land of one or two hectares in size. Furthermore, surrounding parcels could belong to other landowners or be cultivated by other growers. This means strict limitations for a simple WSN topology. First of all, long distances between the considered parcels--often hundreds of meters, or even kilometers--imply that it is not feasible to use common node resources to communicate data from one parcel to another. Wiring parcels could also be unfeasible due to property rights or natural obstacles (e.g., rivers, roads or precipices). This strict limitation can also be applicable to links inside parcels and connections between each subnets and base station, since it is not always possible or advisable to place it near the fields, so long distances could be involved. The solution of simply providing more powerful radio links would not be feasible, since this decreases batteries lifetime and increases node weight and size. The second problem that WSN-based system has to deal with is the problem of communications between the nodes of each mesh network. Although the nodes are placed on the fields in a non-absolute random fashion, they try to organize themselves in a mesh topology. This structure improves reliability, but it is not enough since mesh communications are not always available. Communication problems arise since a vineyard is a dynamic natural system: nodes are subject to dense foliage growth (e.g., see Figure 1), animal intrusions and constant climatological changes. Thus, the internal communications in a cluster can be fully or partially affected, dividing the cluster in several sub-clusters or even isolating one or several nodes. Since the manual repositioning of the nodes periodically is an impractical solution, over-sizing the network would be the only solution in order to decrease the probability for the lack of communication.