# Behavior Composition for Marine Pollution Source Localization Using a Mobile Sensor Network
## 4 Results and Discussion  
### Parameter Selection  
There are five parameters in the uGA: population size \(m\); mutation probability \(p_{m}\); and three time-cycle thresholds, \(th_{l}\), \(th_{a}\), and \(th_{m}\) that satisfy \(th_{l}<th_{a}<th_{m}\). The values of \(th_{l}\) and \(th_{m}\) were empirically set as 5 and 5000, respectively. In the cases that \(gld>5\) and \(gld>5000\), it is reasonable to declare that the SN has lost contact with the plume and the CPSL process has failed, respectively. Moreover, to investigate the influence of the crossover operation on the performance of uGA, an additional variable is considered in the simulation: the crossover type, denoted as \(cTy\). The cases \(cTy=1\), 2, and 3 mean that the one-point crossover, two-point crossover, and uniform crossover are employed in uGA, respectively. Therefore, the values of \(m\), \(p_{m}\), \(th_{a}\), and \(cTy\) should be selected for subsequent simulations.  
To efficiently determine the optimal value combination of \(m\), \(th_{a}\), \(cTy\), and \(p_{m}\), the orthogonal experimental design method [24] was used. The parameters \(m\), \(th_{a}\), \(cTy\), and \(p_{m}\) were taken as orthogonal experimental factors, such that \(m\in\{10,20,30\}\), \(th_{a}\in\{20,40,60\}\), \(cTy\in\{1,2,3\}\), and \(p_{m}\in\{0.3,\,0.5,\,0.8\}\), respectively. There are nine different value combinations in the \(L_{9}(3^{4})\) orthogonal experiments. With respect to each value combination, the results of 20 simulation trials were recorded and averaged. Table 3 presents the average results.  
The small localization errors in Table 3 indicate that the termination criterion of uGA can successfully declare the chemical source in the FPSP. Empirically, if the distance between the real and localized pollution source positions is smaller than 1 m, the SN can easily find the real pollution source when it arrives at the localization position-result. Moreover, the differences among the localization errors are minor when the values of \(m\), \(th_{a}\), \(cTy\), and \(p_{m}\) vary within the 16 different value combinations. This is because the localization result is determined by the termination criterion, which is fixed to the same value for the different simulations in Table 3. Thus, the localization results are hardly influenced by the different parameter values of uGA.  
\begin{table}
\begin{tabular}{c c c} \hline  & **SS** & **uGA** \\ \hline _Contacting the plume_ & Upwind sprint & Upwind sprint \\ _To reacquire the plume_ & Spiraling & Move to candidate chromosomes \\ _Cooperation_ & Simple communications & Customized chromosome crossover \\ _Termination_ & Source distance & LCPs convergence \\ \hline \end{tabular}
\end{table}
Table 2: Similarity and differences between the SS and uGA methods.  
However, the spent cycles, that is, the number of time cycles spent by the MSN from the beginning to termination, are prominently influenced by four orthogonal experimental factors. This is mainly because the values of \(m\), \(th_{a}\), \(cTy\), and \(p_{m}\) can influence the degrees of exploitation and exploration in uGA. The value of \(m\) defines the length of the memorized detection points that are exploited by the C-behavior. \(th_{a}\) and \(cTy\) determine the time-span and manner of exploiting memorized information. \(p_{m}\) has a positive impact on the exploration ability of uGA. The value combination {\(m\), \(th_{a}\), \(cTy\), \(p_{m}\)} = {20, 20, 2, 0.8}, which obtained the minimal averages and standard deviations (std) of the spent cycles in Table 2, is used for the following comparison experiments.