**5. Conclusions**

In this study, two commonly used TEC detrending methods were evaluated for the detection of lightning events in a low latitude region. The results show that a Savitzky– Golay filter of order 6 with a time window length of 120 min best detected the occurrence of lightning compared to the other parameters used in the study. The evaluation was done on the individual satellites rather than the average TEC over a station, as in some studies cited [13]. The individual satellite approach offers a better view than the average approach, as some minute details may be missed or cancelled out during the averaging. In addition, the best time frame being 120 min shows the potential of lightning to inducing TID. Further investigation is suggested in order to explore this observation.

**Author Contributions:** L.O.-P. conceptualized the work. Research design was done by L.O.-P. and W.C., L.O.-P., L.T. and C.M. contributed to data processing and analysis. W.C. and C.M. supervised the work. Manuscript writing and editing was done by all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Shenzhen Science and Technology Innovation Commission (Project No. JCYJ20170818104822282), the Hong Kong RGC Joint Research Scheme (E-PolyU501/16), the Smart City Research Institute, Hong Kong Polytechnic University and National Natural Science Foundation of China (Grant number 41804021).

**Data Availability Statement:** The Dst-index data (IAGA 2002-like format) can be obtained from the Data Analysis Center for Geomagnetism and Space Magnetism, Kyoto University, operating WDC for Geomagnetism, Kyoto (http://wdc.kugi.kyoto-u.ac.jp/Dstae/index.html, accessed on 14 June 2019). The Dst indices were obtained from the GSFC/SPDF OMNIWeb interface at http: //omniweb.gsfc.nasa.gov, accessed on 14 June 2019. The GNSS data can be obtained from Hong Kong SatRef of the Lands Department of the Hong Kong Government. (https://www.geodetic.gov. hk/en/rinex/downv.aspx, accessed on 14 June 2019).

**Acknowledgments:** The authors thank the anonymous reviewers for their useful and insightful comments in improving the manuscript.

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

#### **References**

