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Hazards","award":["JY2023B42"],"award-info":[{"award-number":["JY2023B42"]}]},{"name":"Investigation of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) Mechanism before the Natural Hazards","award":["ZY20215143"],"award-info":[{"award-number":["ZY20215143"]}]},{"name":"Investigation of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) Mechanism before the Natural Hazards","award":["42104159"],"award-info":[{"award-number":["42104159"]}]},{"name":"Investigation of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) Mechanism before the Natural Hazards","award":["20150109"],"award-info":[{"award-number":["20150109"]}]},{"name":"Investigation of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) Mechanism before the Natural Hazards","award":["FZ224104"],"award-info":[{"award-number":["FZ224104"]}]},{"name":"Open Project Fund of Hebei Key Laboratory of Seismic Disaster Instrument and Monitoring Technology","award":["JY2023B42"],"award-info":[{"award-number":["JY2023B42"]}]},{"name":"Open Project Fund of Hebei Key Laboratory of Seismic Disaster Instrument and Monitoring Technology","award":["ZY20215143"],"award-info":[{"award-number":["ZY20215143"]}]},{"name":"Open Project Fund of Hebei Key Laboratory of Seismic Disaster Instrument and Monitoring Technology","award":["42104159"],"award-info":[{"award-number":["42104159"]}]},{"name":"Open Project Fund of Hebei Key Laboratory of Seismic Disaster Instrument and Monitoring Technology","award":["20150109"],"award-info":[{"award-number":["20150109"]}]},{"name":"Open Project Fund of Hebei Key Laboratory of Seismic Disaster Instrument and Monitoring Technology","award":["FZ224104"],"award-info":[{"award-number":["FZ224104"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Ionospheric disturbances are mainly caused by solar and Earth surface activity. The electromagnetic data collected by the CSES (China Seismo-Electromagnetic Satellite, popularly known as the Zhangheng-1 satellite) can capture many space disturbances. Different spatial disturbances can exhibit distinctive shapes on spectrograms. Constant-frequency electromagnetic disturbances (CFEDs) such as artificially transmitted VLF radio waves, power line harmonics, and satellite platform disturbances can appear as horizontal lines on spectrograms. Therefore, we used computer vision and machine learning techniques to extract the frequency of global CFEDs and analyze their strong spatial signal characteristics. First, we obtained time-frequency spectrograms from CSES VLF electric-field waveform data using Fourier transform. Next, we employed an unsupervised clustering algorithm to automatically recognize CFED horizontal lines on spectrograms, merging horizontal lines from different spectrograms, to obtain the CFED horizontal-line frequency range. In the third stage, we verified the presence of CFEDs in power spectrograms, thus extracting their true frequency values. Finally, for strong CFED signals, we generated eight revisited periods, resulting in 10,230 power spectrograms for analyzing each CFED\u2019s spatial characteristics using a combined periodic sequence and spatial region that included frequency offsets, frequency fluctuations, and signal non-observation areas. These findings contribute to enhancing the quality of CSES observational data and provides a theoretical basis for constructing global CFED spatial background fields and earthquake monitoring and early prediction systems.<\/jats:p>","DOI":"10.3390\/rs15153815","type":"journal-article","created":{"date-parts":[[2023,7,31]],"date-time":"2023-07-31T10:00:15Z","timestamp":1690797615000},"page":"3815","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Spatial Characteristics of Global Strong Constant-Frequency Electromagnetic Disturbances from Electric-Field VLF Data of the CSES"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4481-0534","authenticated-orcid":false,"given":"Ying","family":"Han","sequence":"first","affiliation":[{"name":"Institute of Disaster Prevention, Sanhe 065421, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6604-0003","authenticated-orcid":false,"given":"Qiao","family":"Wang","sequence":"additional","affiliation":[{"name":"National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jianping","family":"Huang","sequence":"additional","affiliation":[{"name":"National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jing","family":"Yuan","sequence":"additional","affiliation":[{"name":"Institute of Disaster Prevention, Sanhe 065421, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4436-3845","authenticated-orcid":false,"given":"Zhong","family":"Li","sequence":"additional","affiliation":[{"name":"Institute of Disaster Prevention, Sanhe 065421, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yali","family":"Wang","sequence":"additional","affiliation":[{"name":"Institute of Disaster Prevention, Sanhe 065421, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jingyi","family":"Jin","sequence":"additional","affiliation":[{"name":"College of Computer Science and Technology, Jilin University, Changchun 130012, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xuhui","family":"Shen","sequence":"additional","affiliation":[{"name":"National Space Science Center, Chinese Academy of Sciences, Beijing 100085, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,7,31]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"79","DOI":"10.26464\/epp2018050","article-title":"Examples of unusual ionospheric observations by the CSES prior to earthquakes","volume":"2","author":"Yan","year":"2018","journal-title":"Earth Planet. 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