## 2 Fundamentals of Aerial Wireless Sensor Networks for Oceanographic Monitoring.
### Hw/Sw Solutions for Node Implementation  
Some sensor node implementations reuse commercial solutions (MicaZ(r), TelosB(r), Mica2(r), _etc._) which come with an incorporated microprocessor, and communications electronics (radio modules, antennas, _etc._). These motes normally come with a set of software development tools (operating system, programming languages, reusable components, _etc._) and after-sales technical support from the supplier. When the characteristics of such commercial motes are inadequate or unsuitable, sensor nodes are commonly developed from scratch using the electronic components shown in Figure 1.  
The main component is a low-power microprocessor, which is the core of the platform and is responsible for managing node operation. This microprocessor must possess certain features if it is to be suitable for use with an A-WSN: its architecture, combined with some low power modes, has to be optimized to achieve extended battery life in portable measurement applications. Also, it must include several universal serial synchronous/asynchronous communication interfaces (such as UART, I2C, SPI, _etc._) so that the sensors can be integrated with different types of electrical signals.  
The lifetime of the network depends on the autonomy of the sensor nodes. Power is normally supplied by batteries (commonly D-cell, Lithium-ion, AA or AAA batteries), which may be supplemented by harvesting systems (solar panels, eolic generators, _etc._) to prolong the useful life of the sensor node. It is sometimes necessary to adapt the voltage between the node's power supply and the rest of the components, by means of DC/DC converters.  
Inclusion of a FLASH read/write permanent memory (SD, MMC, _etc._) enhances the robustness of the mote by allowing data to be stored and transmitted later on when conditions permit, thus avoiding loss of information.  
Another important component is a low-consumption clock operating in real time. With a clock synchronized with all the other motes, when a reading is taken from a sensor it can be stored along with the exact time of the reading. Later on, the information can be relayed to the data server, which is important when it comes to analysing the resulting data.  
Sensor node software development can be done in two ways. The first and most immediate is to use specific operating systems (such as TinyOS, Contiki, MANTIS, among others) for these platforms. Although at first this way of proceeding offers advantages for the reuse of WSN libraries, it has however the drawback of limiting the hardware platforms available (e.g., due to the delay between the  
\begin{table}
\begin{tabular}{c c} \hline
**Measured Parameter** & **Unit** \\ \hline _Air temperature_ & \({}^{\circ}\)C, \({}^{\circ}\)F \\ _Air pressure_ & mb \\ _Wind speed_ & m/s \\ _Wind direction_ & degrees \\ _Precipitation_ & mm, inch \\ _Amospheric pressure_ & mmHg \\ _Relative humidity_ & \%RH \\ _Solar radiation_ & W/m\({}^{2}\) \\ _Surface salinity_ & ppt \\ _Surface conductivity_ & S/m \\ \hline \end{tabular}
\end{table}
Table 3: Surface sensors.  
date in which a new microprocessor appears on the market until it is supported by operating systems). The second possibility is to develop the control of the sensor node using software libraries provided by the microprocessor manufacturer. These libraries allow users to manage both the communications and interfaces using well known standards. This option therefore offers greater possibilities for ad-hoc development since it covers more platforms and more interfaces. However, it requires much more experience on the part of developers and reuse is rather limited.