{"refrec":{"BRefID":436646,"RR":"<b>Moradi, M.; van der Molen, J.; Serre-Fredj, L.; Arabi, B.</b> (2025). Identification of clear-sky periods and cloudiness using diffuse-to-direct spectral ratios of hyperspectral solar irradiance and sky radiance measurements. <i>Earth Sci. Inform. 18(3)</i>: 493. <a href=\"https://dx.doi.org/10.1007/s12145-025-01989-5\" target=\"_blank\">https://dx.doi.org/10.1007/s12145-025-01989-5</a>","BEntID":434476,"PublicFlag":1,"CheckedFlag":0,"wosflag":1,"vabbflag":0,"RefStringPartII":". <i>Earth Sci. Inform. 18(3)</i>: 493. <a href=\"https://dx.doi.org/10.1007/s12145-025-01989-5\" target=\"_blank\">https://dx.doi.org/10.1007/s12145-025-01989-5</a>","DocTypID":8,"DocType":"Journal article","MarineFlag":0,"FreshFlag":0,"BrackishFlag":0,"TerrestrialFlag":0,"Authorstring":"Moradi, M.; van der Molen, J.; Serre-Fredj, L.; Arabi, B.","OrigTitleTranslFlag":0,"Authorstringtrunc":"Moradi, M. <i>et al.</i>","Englishabstract":"<span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">Accurate identification of clear-sky and cloudy periods from hyperspectral radiometric data is essential for atmospheric and remote sensing studies. Traditional approaches that rely on single-wavelength spectral ratios often fail under broken-clouds due to rapid irradiance fluctuations and aerosol interference. This study introduces a new method based on the spectrally integrated diffuse-to-direct irradiance ratio (</span><i>IDR</i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">), which is derived from modeled hyperspectral components and provides a robust indicator of sky conditions. The model is developed using 15-year hyperspectral measurements of solar downwelling irradiance (</span><i>E<sub>S</sub></i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">(λ), mW m</span><sup>-2</sup><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> nm</span><sup>-1</sup><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">) and sky radiance (</span><i>L<sub>S</sub></i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">(λ), mW m</span><sup>-2</sup><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> nm</span><sup>-1</sup><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> sr</span><sup>-1</sup><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">) collected in a fixed coastal station located at the Marsdiep tidal inlet in the Dutch Wadden Sea. The model is validated against reference clear-sky periods identified using established clear-sky models and detection algorithms based on simultaneous Global Horizontal Irradiance (</span><i>GHI</i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">) measurements. Results show that </span><i>IDR</i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> thresholds of ≤ 0.35 for clear skies and ≥ 0.70 for overcast conditions achieve high agreement (95% and 92%, respectively) with reference sky classifications. The </span><i>IDR</i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> effectively accounts for the influence of rapidly changing cloud cover in intermediate conditions, ensuring robust classification of clear-sky and overcast periods. The classification is further supported by spectral analysis using Principal Component Analysis, which confirm the stability of diffusive component to </span><i>E<sub>S</sub></i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">(λ) features and the interferences of </span><i>L<sub>S</sub></i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">(λ)/</span><i>E<sub>S</sub></i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\">(λ) ratio across different sky conditions. This work highlights the importance of the diffuse irradiance component role in hyperspectral sky classification. Future research should validate </span><i>IDR</i><span style=\"background-color:rgb(255,255,255);color:rgb(34,34,34);\"> with direct diffuse irradiance measurements to enhance the proposed model under diverse atmospheric conditions.</span>","AbstractOtherLang":null,"BibLvlCode":"AS","StandardTitle":"Identification of clear-sky periods and cloudiness using diffuse-to-direct spectral ratios of hyperspectral solar irradiance and sky radiance measurements","OrigTitleLangCode":"en","OrigTitleLangCodeExtended":"eng","OrigTitleLangID":15,"DateLastModified":{"date":"2026-06-10 01:33:04.043463","timezone_type":1,"timezone":"+02:00"},"UserAccessRight":null,"UserAccID":null,"AuthorKeywords":"Sky classification; Hyperspectral radiometry; Clear-sky detection; Global horizontal irradiance; Wadden sea","OtherDescriptors":null,"Notes":null,"AnaPub":2025,"MonPub":null,"DateUpdate":"2025-12-16","DateCreate":"2025-12-16","SecASFANote":null,"ConfID":null,"PeerRev":1,"VlizCoreFlag":1,"WoScode":null,"VABBcode":null,"OpenAcc":1,"DOI":"10.1007/s12145-025-01989-5"},"refs":null,"anarec":{"AnaID":436646,"PubliDate":2025,"Pagination":"493","XtraPublOfAnaID":null,"ISBN":null,"Volume":"18","Issue":"3","BRefMon":null,"BRefMonRR":null,"BRefXtra":null,"BRefXtraRR":null,"SerBRefID":247421,"SerRR":"Earth Science Informatics. 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