## 2 Materials and Methods
### Data Analysis Using Occupational and General Public Exposure Levels  
First, we analysed the environment or background EF levels, where all of the transmitters and antennas that were installed on the bridge roof were turned off at each measurement point. As the EF levels were not measured on the same day for all transmitters, the background fields were measured on each day. On average, those values were observed ranging from 0.000 to 0.003 V/m. The background electric field values at different locations were subtracted from all of the other measured data, and negative numbers were rounded to zero. The probability distribution of the EF levels was observed in order to test the normality of the distribution. The sample sizes used were: for the bridge roof \(N=\) 176, the bridge deck \(N=\) 264 and the upper deck \(N=\) 88. For each set of measurements (one location at one data collection protocol), we calculated the mean and the standard deviation of each dataset. The geometric mean is more applicable than the arithmetic mean (AM) for explaining the relative progress of the EF level values. Therefore, we computed the geometric mean (GM) of each dataset to estimate the population. Nevertheless, the percentage of measurements equal to or greater than 14 V/m (50% of the ICNIRP exposure limit) and 28 V/m (the ICNIRP exposure limit) were calculated. The interquartile range (IQR) is a vital estimate of the spread of the data, as changes in the upper and lower 25% of the data do not affect it. As an estimate, the IQR is more representative than the standard deviation of the spread of the data, if there are outliers. When the data are from a normal distribution, the IQR is less efficient than the standard deviation; however, we found that our data did not have a normal distribution. Therefore, we analysed the interquartile range of the datasets to perceive how data spread over the 25 th (first quartile) and 75 th (third quartile) percentiles. The EF measurements were analysed and compared in all 3 levels of the ship (upper deck, bridge deck and bridge roof) and the operating conditions of the vessels' transmitters and antennas. For comparison, we used box-and-whiskers plots to show these values. Then, we compared the exposure values with the general public exposure levels of the ICNIRP and the ARPANSA limits in order to quantify the effects. All analyses were carried out using MATLAB (MathWorks Inc., Natick, MA, USA) R2014b on a computer with an Intel Core Intel Core i7 CPU. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Frequency** & **General Public (V/m)** & **Occupational (V/m)** \\ \hline \multicolumn{3}{c}{**ICNIRP Guidelines**} \\ \hline
100 kHz–3 GHz & 28.0–87.0 & 61.0–610.0 \\
3 MHz–18 GHz & 28.0–61.0 & 61.0–203.03 \\ \hline \multicolumn{3}{c}{**ARPANSA Standards**} \\ \hline
100 kHz–3 GHz & 27.4–86.8 & 61.4–614.0 \\
3 MHz–18 GHz & 27.4–61.4 & 61.4–204.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The occupational and general public exposure levels of the ICNIRP guidelines and the ARPANSA standards. The regulation and recommendations about the health and environmental effects on all aspects of non-ionizing radiation exposure was given by the independent scientific organization, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [1]. In Australia, the occupational and general public exposure levels are mandated by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) standards: \"Radiation Protection Standard for Maximum Exposure Levels to Radio frequency Fields-3 kHz to 300 GHz\", 2002 (ARPANSA Radiation Protection Standard No. 3 (RPS3)) [4]. These documents provide reference levels, hence providing verification of compliance with the basic restrictions of the standards. This requires measurements of the highest RF field levels emitted under normal operating conditions and the maximum expected duty factor in areas accessible to workers or the general public [4].