Person: Torres Escribano, José Luis
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Torres Escribano
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José Luis
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Ingeniería
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ISC. Institute of Smart Cities
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0000-0001-9275-8158
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241
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Publication Open Access Evaluation of two procedures for selecting the CIE standard sky type using high dynamic range images(International Solar Energy Society, 2019) García Ruiz, Ignacio; Blas Corral, María Ángeles de; Torres Escribano, José Luis; Hernández Salueña, Begoña; Sáenz Gamasa, Carlos; Ormazábal Pagola, Mikel; Ingeniería; Ingeniaritza; Ciencias; Zientziak; Gobierno de Navarra / Nafarroako GobernuaThe characterization of sky conditions according to the CIE Standard General Sky classification requires knowledge of diffuse luminance angular distribution in the sky vault. This variable is usually measured by sky scanners. However, commercial sky scanners have different drawbacks related to their resolution and measurement time. An alternative to these devices is the use of sky images captured with a digital camera equipped with a fisheye lens. The range of luminances that may occur in the sky makes it necessary to use high dynamic range (HDR) images obtained by the fusion of a series of low dynamic range (LDR) images. Two procedures for the characterization of sky conditions according to the CIE standard using HDR images have been applied and evaluated.Publication Open Access Luminance calibration of a full sky HDR imaging system using sky scanner measurements(Solar Energy Society, 2022) García Ruiz, Ignacio; Sáenz Gamasa, Carlos; Hernández Salueña, Begoña; García Santos, Rafael; Torres Escribano, José Luis; Zientziak; Ingeniaritza; Institute of Smart Cities - ISC; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; IngenieríaA full sky High Dynamic Range imaging system, based on a Single-Lens Reflex camera with a fisheye lens, has been constructed and calibrated with a sky scanner luminance meter. The method considers the geometrical, spectral, timing and orientation issues between instruments. The calibration data sets, having nearly simultaneous measurements under stable sky conditions, were obtained from approximately one month of data using selection variables based in the experimental design. For luminance estimation we use the standard 𝐶𝐼𝐸𝑌 RGB combination and a Spectrally Matched Luminance (𝑆𝑀𝐿) predictor, matching the spectral response of the instruments. With 738 calibration points having luminances up to 23.6 kcd∕m2, covering 98.5% of the sky luminance range, 𝐶𝐼𝐸𝑌 is linearly correlated with sky scanner measurements with a coefficient of determination 𝑅2 = 0.9927 and a Root Mean Squared Error (𝑅𝑀𝑆𝐸) of 7.7%. 𝑆𝑀𝐿 gives better results, with 𝑅2 = 0.9973 and 𝑅𝑀𝑆𝐸 = 5.3%. With 253 calibration points with luminances up to 12.9 kcd∕m2, comprising 94.1% of the sky luminance range, both predictors clearly improve, with 𝑅2 = 0.9964 and 𝑅𝑀𝑆𝐸 = 4.1% in case of 𝐶𝐼𝐸𝑌 and 𝑅2 = 0.9982 and 𝑅𝑀𝑆𝐸 = 2.9% in case of 𝑆𝑀𝐿.