# Underwater Optical Path Loss after Passage of a Tropical Storm
## 6 Conclusions  
This study identified the typhoon effects on UWOC in the western North Pacific Ocean by solving a 2D RTE numerically with the data collected by three NAVOCEANO Seagliders. The beam attenuation coefficient \(c\) (470 nm) was measured from June 25 to June 30, 2012 after Super Typhoon Guchol's passage and from January 6 to February 28, 2014 with no typhoon activity. A huge difference was found in the horizontally averaged \(c\), greater than 0.8 m\({}^{-1}\) during Typhoon Guchol's passage and with much smaller values, less than 0.05 m\({}^{-1}\), without typhoon activity. The volume back scattering coefficient \(b(z)\) was calculated from the observed beam attenuation coefficient \(c(z)\) with a single scattering albedo \(\omega=0.75\). The 2D Henyey-Greenstein (H-G) phase function was used for the azimuthally symmetric and strong forward scattering with \(g=0.924\). After discretization in position and direction, the 2D RTE becomes a set of algebraic equations. The Gauss-Seidel iteration was used to solve the 2D RTE and in turn to calculate the normalized received power using observed IOPs from the NAVOCEANO Seagliders with and without the influence of a typhoon. The simulated results show that Super Typhoon Gochul destroyed the UWOC due to the rapid reduction of normalized power from 1 at the surface to 10\({}^{-1}\) (practically 0) at \(z=40\) m, in comparison to 1.0 to 0.1 at \(z=40\) m without typhoon passage.  
The results only show the strong typhoon effect through comparison between NG226 and NG270 during two periods: June 25-30, 2012 and January 6-February 28, 2014. These two short durations are not enough to conclude and affirm the feasibility of using UWOC in the western North Pacific Ocean without typhoon passage because it is well known that the IOPs of the underwater channel can be easily affected by phenomena such as wind, surface waves, optical turbulences, and water currents. Furthermore, the actual UWOC analysis is thin here since developing a full communication system model is beyond the scope of the current effort. The communication link performance has not been evaluated due to the limited amount of available data. It will be investigated in future studies using a more complete dataset and UWOC link models.  
Figure 4: (**a**) Cross section of the observed volume attenuation coefficient c(\(z\)) along the tracks of NAVOCEANO Seaglider NG226 from January 25 to January 30, 2012, after Super Typhoon Guchol’s passage, and (**b**) the calculated normalized received power \(P_{n}(z)\). The horizontal axis shows the glider’s location along the blue-colored track in Figure 2b with Station-1 located at 25\({}^{\circ}\)30\({}^{\prime}\)20\({}^{\prime\prime}\) N, 131\({}^{\circ}\)59\({}^{\prime}\)51\({}^{\prime\prime}\) E at 03:19 UTC, June 25, 2012, and Station-59 at 24\({}^{\circ}\)59\({}^{\prime}\)27\({}^{\prime\prime}\) N, 131\({}^{\circ}\)59\({}^{\prime}\)26\({}^{\prime\prime}\) E at 17:24 UTC, June 30, 2012. It is noted that Super Typhoon Guchol moved out of the area on June 18, 2012.  
**Author Contributions:** Conceptualization, P.C.C.; methodology, P.C.C.; software, C.F.; validation, C.F.; formal analysis, P.C.C.; investigation, C.F.; resources, P.C.C.; data curation, C.F.; writing--original draft preparation, P.C.C.; writing--review and editing, P.C.C.; visualization, C.F.; supervision, P.C.C.; project administration, P.C.C.; funding acquisition, P.C.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Office of Naval Research.  
We thank the Naval Oceanographic Office for the use of optical data from three Seagliders.  
The authors declare no conflicts of interest.