# Event Coverage Detection and Event Source Determination in Underwater Wireless Sensor Networks
## 3 Event Detection and Sensory Data Aggregation
This figure shows that the energy consumption for our gathered strategy is smaller than that for the traditional non-gathered strategy, especially when \(r\) is relatively small. Figure 2:8 Comparison of the number of sensory data packets when the transmission radius \(r\) is set to various values, for the strategies that sensory data are gathered, or not gathered, by relay nodes. This figure shows that our gathered strategy requires a smaller number of sensory data packets than the number that non-gathered strategy requires, especially when \(r\) is set to a relatively small value. Figure 11 shows the number of control packets generated by (i) our technique and (ii) CARP as the routing protocol, when the transmission radius is set to 0.1, 0.15, 0.2 or 0.25, respectively. The number of sensor nodes, which drift with the water dynamics and change their coordinates, is set to 30 or 50, respectively, where the \(x\)- and \(y\)-coordinates of these sensor nodes change no more than 3-5 m and their \(z\)-coordinate changes no more than 0-3 m, per time slot. There are 30 sensor nodes at each time slot whose sensory data deviate from a normal sensing range. The other parameters are set to the same values as those in Figure 2:9 Figure 11 shows that the number of control packets for CARP is the same when the number of moving sensor nodes varies, since CARP reselects relay nodes whenever sensory data are required to be routed to SN, and hence, the number of control packets is not impacted by the number of moving sensor nodes. On the other hand, the number of control packets generated by our technique is much smaller than that by CARP, when the number of sensor nodes, which drift with the water dynamics and change their coordinates, is relatively smaller. This is due to the fact that when the network topology is relatively steady, the number of parent nodes, which are determined in previous time slot(s) and can be reused for routing sensory data to SN in the forthcoming time slots, are relatively larger in number. Therefore, the number of \(HeartB_{ext}\)-EPONG control packets is smaller. Besides, when the communication radius \(r\) is relatively large, the parent-child relation for a larger number of sensor nodes can be maintained, although their coordinates have been changed. This is reflected by Figure 4:0 the difference in the number of control packets is smaller for \(r=0.25\) than that for \(r=0.1\). Generally, a smaller number of control packets is generated by our technique than by CARP, especially when the network topology is relatively steady. Figure 12 shows the energy consumption for (i) our technique and (ii) CARP as the routing protocol. The transmission radius \(r\) is set to 0.1, 0.15, 0.2 or 0.25, respectively. The experiments are conducted for 10 and 30 contiguous time slots. There are 30 sensor nodes at each time slot whose sensory data deviate from a normal sensing range. The other parameters are set to the same values as those in Figure 4:1 Figure 12 shows that the energy consumption of our sensory data aggregation strategy is less than that of CARP. This is due to the fact that sensory data, whose value has been varied significantly, are gathered and routed to SN. This means that the partial, rather than the whole of, sensory data should be routed to SN in a certain time slot. However in CARP, all sensory data should be routed to SN, and each data packet should be routed independently. Therefore, more energy is to be consumed for data gathering and routing. Figure 12 also shows that the difference of

Figure 4:2 Comparison of the number of control packets for our technique (SDA) with respect to CARPas the routing protocol, when the transmission radius \(r\) is set to various values, and the number of sensor nodes, which drift with the water dynamics and change their coordinates, is set to various values. This figure shows that the number of control packets generated by our technique is much smaller than that of CARP, especially when the network topology is relatively steady.