{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,4,10]],"date-time":"2025-04-10T17:32:06Z","timestamp":1744306326160,"version":"3.37.3"},"reference-count":122,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2022,3,22]],"date-time":"2022-03-22T00:00:00Z","timestamp":1647907200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"In the past 20 years, many studies have been performed on ballast layer inspection and condition evaluation with ground penetrating radar (GPR). GPR is a non-destructive means that can reflect the ballast layer condition (fouling, moisture) by analysing the received signal variation. Even though GPR detection\/inspection for ballast layers has become mature, some challenges still need to be stressed and solved, e.g., GPR indicator (for reflecting fouling level) development, quantitative evaluation for ballast fouling levels under diverse field conditions, rapid GPR inspection, and combining analysis of GPR results with other data (e.g., track stiffness, rail acceleration, etc.). Therefore, this paper summarised earlier studies on GPR application for ballast layer condition evaluation. How the GPR was used in the earlier studies was classified and discussed. In addition, how to correlate GPR results with ballast fouling level was also examined. Based on the summary, future developments can be seen, which is helpful for supplementing standards of ballast layer evaluation and maintenance.<\/jats:p>","DOI":"10.3390\/s22072450","type":"journal-article","created":{"date-parts":[[2022,3,23]],"date-time":"2022-03-23T03:30:23Z","timestamp":1648006223000},"page":"2450","source":"Crossref","is-referenced-by-count":34,"title":["State-of-the-Art Review of Ground Penetrating Radar (GPR) Applications for Railway Ballast Inspection"],"prefix":"10.3390","volume":"22","author":[{"given":"Shilei","family":"Wang","sequence":"first","affiliation":[{"name":"Infrastructure Inspection Research Institute, China Academy of Railway Sciences Co., Ltd., Beijing 100081, China"}]},{"given":"Guixian","family":"Liu","sequence":"additional","affiliation":[{"name":"Infrastructure Inspection Research Institute, China Academy of Railway Sciences Co., Ltd., Beijing 100081, China"}]},{"given":"Guoqing","family":"Jing","sequence":"additional","affiliation":[{"name":"School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China"}]},{"given":"Qiankuan","family":"Feng","sequence":"additional","affiliation":[{"name":"Infrastructure Inspection Research Institute, China Academy of Railway Sciences Co., Ltd., Beijing 100081, China"}]},{"given":"Hengbai","family":"Liu","sequence":"additional","affiliation":[{"name":"Infrastructure Inspection Research Institute, China Academy of Railway Sciences Co., Ltd., Beijing 100081, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4339-1833","authenticated-orcid":false,"given":"Yunlong","family":"Guo","sequence":"additional","affiliation":[{"name":"Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN Delft, The Netherlands"}]}],"member":"1968","published-online":{"date-parts":[[2022,3,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"36","DOI":"10.1093\/tse\/tdaa031","article-title":"Recent studies on railway-track substructure at TTCI","volume":"3","author":"Li","year":"2021","journal-title":"Transp. 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