A New Method for Computing Ionogram-Based TEC Based on Digisonde data for Disaster Prevention Punyawi Jamjareegulgarn1, Sarun Duangsuwan2, Pornchai Supnithi3, Worachai Srisamoodkham4 [แหล่งตีพิมพ์ : 2020 8th International Electrical Engineering Congress (iEECON) 4-6 March 2020, Chiang Mai, Thailand]