## 4 Results and Discussion
### Energy Consumption Reduction from Proposed Hybrid Technique: Scenario 2  
The results presented in Section 4.1 show that the WSN lifespan obtained from the configurations of scenario 1 is too low. Though we are able achieve real-time leak detection in scenario 1, such a deployment will require frequent battery replacement, thus making it not energy-efficient and suitable for battery-powered WWPM systems. Therefore, there is a need to further decrease the sensor node energy consumption so as to prolong the lifespan of the WWPM system. This sub-section presents and discuss the results of the implementation the hybrid energy reduction technique that adds hierarchical sensing and duty cycling to the already-existing distributed computing at the node level to achieve both low-power consumption and real-time monitoring. For illustration purposes, we implemented the proposed solution on the laboratory testbed and evaluated the power consumption of the ICF algorithm (since it has the highest power consumption as shown in Section 4.1). Figure 8 displays the current profile of sensor node S2, and Figure 9 depicts the battery voltage discharge over a period of 1 day. The measurements presented in these figures were collected using the custom power measurement device we described in Section 2.3. The results in Figure 8 revealed a current consumption of 300 uA (0.99 mW) when the node is in the deep sleep mode. This is significantly close to the theoretical datasheet value of 290 uA (150 uA for ESP32 ULP coprocessor and 140 uA for ADXL344 measurement mode supply current). From the results, it can be seen that there is a significant decrease in the power consumption of the sensor node. When there is no leak on the pipeline, the sensor node consumed a current as low as 0.3 mA when duty cycling and hierarchical sensing were implemented compared to 31.8 mA when duty cycling and hierarchical sensing were not implemented. The results in Figure 9 showed that the battery voltage dropped from 3.78 V to 3.76 V for a period of 1 day when both duty cycling and hierarchical sensing were implemented at the sensor node level. This corresponded to a battery energy consumption of 5.03% compared to 44.53% when duty cycling and hierarchical sensing were not implemented. Thus, it can be seen that the implementation of duty cycling at the sensor node level can lead to an increase in the sensor node's lifetime by a factor of 8. This is because the node stays in the ultra-low power state (where its current consumption is 0.3 mA) whenever there is no leak on the pipeline. Finally, the results presented in this section demonstrates that our proposed solution can achieve real-time leak detection while at the same time preserving the lifespan of the WWPM system. Furthermore, the hierarchical sensing utilized in this hybrid approach does not reduce the leak detection reliability. From [46], it was shown that the magnitude of vibrations resulting from leaks are in the order of 1.01 g, leading to 1.01 g being set as the baseline value for leak detection. Thus, a leak alarm is triggered each time the difference between the estimated pipe surface acceleration and the baseline value exceeds the threshold value (\(\delta\)) by 0.01 g. Such vibrations were effectively detected by the ADXL344 accelerometer when configured in the \(\pm\)2 g sensing range given its sensitivity value of 4096 LSB/g and noise floor level of 530 \(\upmu\)g/\(\surd\)Hz. To be sure of the leak event detected by the ADXL344 accelerometer, the ADXL344 always triggered a wakeup to the LSM9 DS1 accelerometer to make more accurate measurements to confirm the leak event. In this way, the leak detection reliability is not reduced in any way. In conclusion, the eightfold improvement (approximately 480 h or 20 days) observed in scenario 2 compared to scenario 1 still presents a relatively short lifespan in a practical sense. This limited duration arises from the deliberate introduction of leak events every hour for twelve hours within the 1-day experimentation period of scenario 2.