## 5 Discussion
### What is the Infrastructure usually used in Deploying A-WSNs for Oceanographic Monitoring? All the deployments that were implemented were for monitoring of coastal waters. The commonest parameters measured were T, pH, turbidity and Dissolved Oxygen (DO). The commonest topologies were _Star_ and _Partially Connected_. The most commonly used radio frequency band is 2.4 GHz ISM. And finally, eleven of the twelve systems used batteries, and six of the twelve considered using solar panels. Access to and upkeep of the component elements of an oceanographic A-WSN entail a number of added difficulties on top of the ones that arise on land. It is therefore essential to define a system maintenance strategy to minimize the attendant costs and preserve proper functioning. Maintenance of a network once in place essentially has to address three clearly distinct aspects:  
Figure 5: World map showing the location of the projects reviewed. (1) maintenance of sensorization and communication elements (antennas) to prevent loss of functionality or deterioration (biofouling, calibration, orientation, _etc._); (2) maintenance of the power supply (batteries, solar panels, _etc._); and (3) maintenance of the network infrastructure and topology (e.g., performance degradation, synchronization of clocks, vandalism, _etc._). Following are details of the survey results concerning these aspects:  
1. When the buoy system is used for long-term observation, the sensors are susceptible to biofouling (microbial and algal films). Special care must therefore be taken with the quality of the instruments used, since the short-term effects of biofouling can be considerable (the quality of the measurements can sometimes be compromised in less than a week). Many techniques have been studied to prevent biofouling on materials [22]. The following need to be taken in to account when considering biofouling protection for oceanographic sensors: 1. It should not affect measurement or the environment. 2. It should not consume too much energy in order to maximize the autonomy of the monitoring system. 3. It should be reliable even in aggressive conditions. Surface treatment based on antifouling paints is useful mainly to protect the sensor housing. UV radiation is a highly promising alternative that is non-invasive of the marine environment; however, it is not viable with the technology currently available owing to the high energy input that it requires. Another means of protection is to cover the most sensitive elements of the sensor with copper, but again the cost is high. In a word, this is a most important factor that sensor node designers need to take into account. Sensor elements normally have to be calibrated with non-portable instruments, which means that the node has to be accessed and the sensor removed for calibration in the laboratory. Maintenance operations relating to relocation of the sensor node can be performed without withdrawing the node from the network. 2. The node's power supply will require short-, medium- or long-term maintenance depending on the elements used. In normal conditions batteries limit operability to a matter of months, or even weeks [23]. It is therefore necessary to consider the use of renewable energies such as solar, eolic, wave or tidal power to significantly reduce system maintenance requirements. The most widely used is solar power because light energy is available practically constantly, and because of the accumulated experience in integrating solar panels as a supplementary energy source in A-WSN deployments [23]. 3. One of the main challenges for A-WSNs as regards network topology and infrastructure is to achieve a network that functions without sacrificing originally-defined requirements in respect of performance, sensor coverage and connectivity [18]. In oceanographic applications the possibilities of perturbations in the original physical topology are heightened by the fact that the sea is a medium in constant movement (waves, tides, _etc._).