{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,5]],"date-time":"2026-04-05T06:44:36Z","timestamp":1775371476754,"version":"3.50.1"},"reference-count":39,"publisher":"MDPI AG","issue":"16","license":[{"start":{"date-parts":[[2021,8,9]],"date-time":"2021-08-09T00:00:00Z","timestamp":1628467200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000923","name":"Australian Research Council","doi-asserted-by":"publisher","award":["LP170100108"],"award-info":[{"award-number":["LP170100108"]}],"id":[{"id":"10.13039\/501100000923","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>High-density polyethylene geomembranes are employed as covers for the sewage treatment lagoons at Melbourne Water Corporation\u2019s Western Treatment Plant, to harvest the biogas produced during anaerobic degradation, which is then used to generate electricity. Due to its size, inspecting the cover for defects, particularly subsurface defects, can be challenging, as well as the potential for the underside of the membrane to come into contact with different substrates, viz. liquid sewage, scum (consolidated solid matter), and biogas. This paper presents the application of a novel quasi-active thermography inspection method for subsurface defect detection in the geomembrane. The proposed approach utilises ambient sunlight as the input thermal energy and cloud shading as the trigger for thermal transients. Outdoor laboratory-scale experiments were conducted to study the proposed inspection technique. A pyranometer was used to measure the intensity of solar radiation, and an infrared thermal camera was used to measure the surface temperature of the geomembrane. The measured temperature profile was analysed using three different algorithms for thermal transient analysis, based on (i) the cooling constant from Newton\u2019s law of cooling, (ii) the peak value of the logarithmic second derivative, and (iii) a frame subtraction method. The outcomes from each algorithm were examined and compared. The results show that, while each algorithm has some limitations, when used in combination the three algorithms could be used to distinguish between different substrates and to determine the presence of subsurface defects.<\/jats:p>","DOI":"10.3390\/s21165365","type":"journal-article","created":{"date-parts":[[2021,8,9]],"date-time":"2021-08-09T09:03:53Z","timestamp":1628499833000},"page":"5365","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Detection of Defects in Geomembranes Using Quasi-Active Infrared Thermography"],"prefix":"10.3390","volume":"21","author":[{"given":"Yue","family":"Ma","sequence":"first","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Monash University, Wellington Rd, Clayton, VIC 3800, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Francis","family":"Rose","sequence":"additional","affiliation":[{"name":"Defence Science and Technology Group, 506 Lorimer St., Fishermans Bend, VIC 3207, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3227-7648","authenticated-orcid":false,"given":"Leslie","family":"Wong","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Monash University, Wellington Rd, Clayton, VIC 3800, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0991-4293","authenticated-orcid":false,"given":"Benjamin Steven","family":"Vien","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Monash University, Wellington Rd, Clayton, VIC 3800, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Thomas","family":"Kuen","sequence":"additional","affiliation":[{"name":"Melbourne Water Corporation, 990 La Trobe Street, Docklands, VIC 3008, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nik","family":"Rajic","sequence":"additional","affiliation":[{"name":"Defence Science and Technology Group, 506 Lorimer St., Fishermans Bend, VIC 3207, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jayantha","family":"Kodikara","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wingkong","family":"Chiu","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, Monash University, Wellington Rd, Clayton, VIC 3800, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,8,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"631","DOI":"10.1680\/geot.2005.55.9.631","article-title":"Long-term performance of contaminant barrier systems","volume":"55","author":"Rowe","year":"2005","journal-title":"Geotechnique"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Wong, L., Vien, B.S., Ma, Y., Kuen, T., Courtney, F., Kodikara, J., and Chiu, W.K. 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