One of the more common methods of observation of variability of the Earth’s ionosphere is based on total electron content (TEC) estimated from ground-based dual-frequency Global Positioning System (GPS) receivers. Variations in solar, geomagnetic and seismic activity cause depletions or enhancements in the ionospheric electron concentrations that can be detected as disturbances. Some of these disturbances have wave-like characteristics, where frequency of oscillation can be used to identify and classify the disturbance. In this study, the frequency of such periodic disturbances is estimated using a fast Fourier transform (FFT)-based method, namely IONOLAB-FFT, in the spectral domain. IONOLAB-FFT, which was initially developed to be used on slant TEC (STEC), is modified to be applied to TEC in the local zenith direction of the receiver. The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a solar flare, a medium-scale traveling ionospheric disturbance (MSTID), a large-scale TID (LSTID) and an earthquake. An accordance with these known disturbances is observed in running IONOLAB-FFT, and the main frequencies and durations of the disturbances are estimated. IONOLAB-FFT method is applied to TEC computed from Turkish Permanent GPS Network (TNPGN-Active) which lies in mid-latitude region to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June and September months for 2010, 2011 and 2012 years. It is observed that a large number of the estimated frequencies are accumulated between 0.08 and 0.14 MHz corresponding to periods of 3.5 h to 2 h. The significant frequencies are grouped less than 0.28 MHz. A large number of the durations of the oscillations are between 425 and 550 min in 2010, 300 and 550 min in 2011 and 350 and 400 min in 2012. The longest duration (around 800 min: 13.33 h) is observed in December months, and the shortest duration (around 2 h) is observed in September months.

中文翻译：

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使用 IONOLAB-FFT 算法估计土耳其上空电离层扰动的频率和持续时间

观测地球电离层变化的一种更常用的方法是基于从地基双频全球定位系统 (GPS) 接收器估计的总电子含量 (TEC)。太阳、地磁和地震活动的变化会导致电离层电子浓度的消耗或增强，这些可以被检测为干扰。其中一些干扰具有波状特征，其中振荡频率可用于识别和分类干扰。在这项研究中，使用基于快速傅立叶变换 (FFT) 的方法（即 IONOLAB-FFT）在频谱域中估计此类周期性干扰的频率。IONOLAB-FFT 最初开发用于倾斜 TEC (STEC)，经过修改后适用于接收器局部天顶方向的 TEC。该算法使用由地磁活动、太阳耀斑、中尺度移动电离层扰动 (MSTID)、大规模 TID (LSTID) 和地震产生的扰动的文献数据进行测试。在运行 IONOLAB-FFT 时观察到这些已知干扰的一致性，并估计干扰的主要频率和持续时间。IONOLAB-FFT 方法应用于由位于中纬度地区的土耳其永久 GPS 网络 (TNPGN-Active) 计算的 TEC，以检测 12 月、3 月、6 月和 9 月期间的任何波浪状振荡、突然扰动和其他不规则现象2010、2011 和 2012 年。观察到大量估计的频率在 0.08 到 0.14 MHz 之间累积，对应于 3.5 小时到 2 小时的周期。重要频率被分组为小于 0.28 MHz。大量的振荡持续时间在 2010 年在 425 和 550 分钟之间，2011 年在 300 和 550 分钟之间，2012 年在 350 和 400 分钟之间。最长的持续时间（大约 800 分钟：13.33 小时）在 12 月观察到，并且最短的持续时间（约 2 小时）是在 9 月观察到的。