**5. Conclusions**

In the present study, we designed an inversion model of an offshore atmospheric duct using an AIS signal. The model adopted the idea of classification before inversion: Firstly, the classification model of the atmospheric duct was established to judge the type of atmospheric duct. Secondly, the inversion models of the surface and elevated duct parameters were established, and the atmospheric duct parameters were obtained. In this study, the atmospheric duct classification model was established using DNN, and the duct parameters inversion model was established using DNN and GA respectively. Through experimental comparison, the inversion result of atmospheric duct parameters based on the model in our study was better than that of the traditional model. The atmospheric duct classification model in our study attained a classification accuracy of 97%. Comparing the inversion results of the atmospheric duct parameter inversion model established by DNN and GA, we found that the DNN method is more advantageous than the GA method in inverting the elevated duct. Thus, more AIS measured power should be included in the data set, and the model parameters must be optimized in future studies, to improve the inversion accuracy of atmospheric duct parameters.

**Author Contributions:** Conceptualization, J.W. and J.H.; Methodology, J.H.; Software, J.H., Q.Z. and L.Z.; Validation, J.H., J.W. and H.W.; Formal analysis, J.H.; Investigation, J.H.; Resources, J.H. and H.Z.; Data curation C.Z., S.Z. and L.Z.; Writing—original draft preparation, J.H.; Writing—review and editing, J.W., H.W. and H.Z.; Visualization, H.Z.; Supervision, J.W.; Project administration, J.W.; Funding acquisition, H.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China (grant number 42076195).

**Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare that they have no conflict of interest.
