###### Abstract  
In this paper, we are interested in characterizing the link properties of a wireless sensor network with nodes deployed at ground level. Such a deployment is fairly common in practice, e.g., when monitoring the vehicular traffic on a road segment or the status of infrastructures such as bridges, tunnels or dams. However, the behavior of off-the-shelf wireless sensor nodes in these settings is not yet completely understood. Through a thorough experimentation campaign, we evaluated not only the impact of the ground proximity on the wireless links, but also the impact of some parameters such as the packet payload, the communication channel frequency and the topography of the deployment area. Our results show that a ground-level deployment has a significant negative impact on the link quality, while parameters such as the packet size produce unexpected consequences. This allows us to parameter classical theoretical models in order to fit a ground-level deployment scenario. Finally, based on the lessons learned in our field tests, we discuss some considerations that must be taken into account during the design of communication protocols and before the sensor deployment in order to improve network performance. wireless sensor networks; ground deployment; experimental evaluation; links properties 1  
[PERSON], 1,2,3,*,  
at the ground level? (iii) What is the impact (in terms of packet reception ratio (PRR) or received signal strength indicator (RSSI)) of parameters such as transmission power, packet size or communication channel frequency? (iv) What is the impact of the topography of the deployment environment on the link properties? The main particularity of WSNs is their limited resources: these networks are constrained in energy, storage, processing and communication capability. Energy is the strongest constraint because nodes are usually equipped with batteries of limited capacity [12; 13]. In addition to the energy constraint, because of the environmental constraints (obstacles, variable meteorological conditions, etc. ), the instability of the radio link is another factor which significantly influences the performance of these networks [14; 15]. Topology construction and maintenance, localization, data aggregation and routing are some key operations in WSN which need to exploit reliable wireless links. Link quality has an important impact on these upper-layer protocols. Then, understanding the link properties in order to integrate them in the design of communication protocols is a real challenge in WSN. Several works in which the authors theoretically model the radio channel [16; 17; 18] or experimentally evaluate the impact of the deployment environment [14; 15] on the link quality/properties are proposed in the literature. However, to our knowledge, none of the previous experimental studies consider the case where sensors are deployed at the ground level. Our main motivation in this paper is to highlight the significant differences that exist between a wireless link at the ground level and one situated at height. Considering sensors deployed at ground level, we also investigate in this paper the impact of some parameters such as the packet size, the communication frequency and the topography of the area. To understand the properties of radio links in a WSN with nodes deployed in such conditions, we conducted an extensive experimental campaign in which we evaluated the impact of different parameters. Our contributions can be summarized as follows:  
* We experimentally show a significant difference between a ground surface deployment WSN and a WSN in which nodes are deployed at a given height. * We measure the impact of several communication parameters on the radio link properties in a WSN with sensors deployed at ground level. * We compare the obtained results with classical theoretical models, showing that a careful parameterization of the models gives accurate results in general, but some particular situations (very small payload and uphill deployment) deviate from these theoretical explanations.