Thai Covid-19 Wave Breaks Analysis Based on Fourier Transform

Around the beginning of April 2021, the Thai Covid-19 Alpha-Delta wave began to spread. After approximately 37 weeks, the Omicron wave emerged in mid-December 2021. This paper proposes a Fourier transform approach for examining the exact wave breaks and reveals the hidden information in the power spectrum of the pandemic by converting the number of infected cases, death cases, and recovered cases caused by Covid-19 in Thailand from the time domain to the frequency domain. Analyses are conducted on wave intensity, pattern, and cycle duration. Two validation procedures are proposed to ensure the correct identification of wave breaks. The first strategy employs cross-correlation, whereas the second technique utilizes matching peak frequencies. Our results mathematically determined the Alpha-Delta wave’s end date and the Omicron wave’s beginning date. The matched peak frequency between the waves was discovered at frequency 5.286, corresponding to a cycle length of 7.027 days. The outcome enables policymakers to comprehend the pandemic’s trend and determine if the policy should be strengthened or relaxed.