Multivariate Analysis and Classification of 146 Odor Character Descriptors

[EN] Introduction: Smells can be described by assigning the words that come to mind when sniffing an odorous material. A great number of terms can be applied, but not all of them are independent, and it is possible to establish groups of words often applied together when describing a smell. Such classification of olfactory descriptors is of scientific interest in order to better understand the dimensionality and structure of human olfactory perception space. For this purpose, compilations of olfactory profiles contain valuable information that may lead to certain consensus in odor classification. Methods: One of the most comprehensive odor databases is the Dravnieks¿ Atlas, which contains quantitative olfactory profiles for 160 samples. For each one, a large panel rated the applicability of 146 odor character descriptors on a numeric scale. Results: By applying principal component analysis to this Atlas, 105 descriptors were reorganized in 24 classes, and 33 attributes were considered as odors intermediate of two or three categories. The similarities between classes were studied by means of a further multivariate analysis based on latent variables, which provides valuable information about the most salient dimensions of odor space. Conclusions: Consistent with other reported statistical analyses of olfactory databases, the perceptual space of odor character is multidimensional with about 20¿30 dimensions, and it is better described as a continuum spectrum rather than as a segmented space. Implications: Attempts to classify all possible odor descriptors in a restricted number of classes appear to be inappropriate. Instead, 24 categories of related terms are proposed here, regarding the rest as intermediate smells, assuming that olfactory classes are not independent and follow certain hierarchy according to particular underlying dimensions.Partial financial support was received from the Spanish Ministry or Education and Science under grant no. FU2004-1119.Zarzo Castelló, M. (2021). Multivariate Analysis and Classification of 146 Odor Character Descriptors. Chemosensory Perception. 14(2):79-101. https://doi.org/10.1007/s12078-021-09288-1S7910114

Multivariate analysis of olfactory profiles for 140 perfumes as a basis to derive a sensory wheel for the classification of feminine fragrances

[EN] In order to guide consumers in their purchase of a new fragrance, one approach is to visualize the spectrum of men's or women's fragrances on a two-dimensional plot. One of such sensory maps available is the Hexagon of Fragrance Families. It displays 91 women's perfumes inside a polygon, so that each side accounts for a different olfactory class. In order to discuss this chart, odor profiles were obtained for these fragrances and additional feminine ones (140 in total, launched from 1912 to 1990). An olfactory dataset was arranged by coding numerically the descriptions obtained from Fragrantica and Osmoz websites, as well as from a perfume guide. By applying principal component analysis, a sensory map was obtained that properly reflected the similarities between odor descriptors. Such representation was equivalent to the map of feminine fragrances called Givaudan Analogies, comprised of five major categories. Based on the results, a modified version of the Hexagon based on 14 categories was proposed. The first principal component explained preference for daytime versus nighttime wear, and regression models were fitted in order to estimate such preferences according to the odor profiles. The second component basically discriminated floral versus chypre (mossy-woody) fragrances. Results provide a fundamental basis to develop standard sensory maps of women's fragrances.Zarzo Castelló, M. (2020). Multivariate analysis of olfactory profiles for 140 perfumes as a basis to derive a sensory wheel for the classification of feminine fragrances. Cosmetics. 7(11):1-20. https://doi.org/10.3390/cosmetics7010011S120711Kaeppler, K., & Mueller, F. (2013). Odor Classification: A Review of Factors Influencing Perception-Based Odor Arrangements. Chemical Senses, 38(3), 189-209. doi:10.1093/chemse/bjs141Osmoz Website for Olfactory Exploration of Men’s and Women’s Commercial Fragrances http://www.osmoz.com/perfumes/searchFragrantica Online Encyclopedia of Perfume https://www.fragrantica.com/search/Eurofragrance 2011: Feminine Fragrances Genealogy. Barcelona, Spain http://www.eurofragance.com/docs/26_2011_fem_geneology_eurofragance.jpgWorld of Perfumes; Caravan Fragancias SL: Zaragoza, Spain https://www.caravanfragancias.es/content/7-mundo-del-perfumeZarzo, M., & Stanton, D. T. (2009). Understanding the underlying dimensions in perfumers’ odor perception space as a basis for developing meaningful odor maps. Attention, Perception & Psychophysics, 71(2), 225-247. doi:10.3758/app.71.2.225Zarzo, M. (2015). Underlying dimensions in the descriptive space of perfumery odors: Part II. Food Quality and Preference, 43, 79-87. doi:10.1016/j.foodqual.2015.02.018Teixeira, M. A., Barrault, L., Rodríguez, O., Carvalho, C. C., & Rodrigues, A. E. (2014). Perfumery Radar 2.0: A Step toward Fragrance Design and Classification. Industrial & Engineering Chemistry Research, 53(21), 8890-8912. doi:10.1021/ie403968wCadoret, M., Lê, S., & Pagès, J. (2009). A Factorial Approach for Sorting Task data (FAST). Food Quality and Preference, 20(6), 410-417. doi:10.1016/j.foodqual.2009.02.010Kostov, B., Bécue-Bertaut, M., & Husson, F. (2014). An original methodology for the analysis and interpretation of word-count based methods: Multiple factor analysis for contingency tables complemented by consensual words. Food Quality and Preference, 32, 35-40. doi:10.1016/j.foodqual.2013.06.009Veramendi, M., Herencia, P., & Ares, G. (2013). Perfume Odor Categorization: To What Extent Trained Assessors and Consumers Agree? Journal of Sensory Studies, 28(1), 76-89. doi:10.1111/joss.12025Zarzo, M. (2019). Understanding the Perceptual Spectrum of Commercial Perfumes as a Basis for a Standard Sensory Wheel of Fragrances. Cosmetics, 7(1), 3. doi:10.3390/cosmetics7010003Olfactive Families of Fragrances according to the French Society of Perfumers https://www.parfumeurs-createurs.org/fr/filiere-parfum/les-familles-olfactives-102Chastrette, M., Elmouaffek, A., & Sauvegrain, P. (1988). A multidimensional statistical study of similarities between 74 notes used in perfumery. Chemical Senses, 13(2), 295-305. doi:10.1093/chemse/13.2.295Boelens, H. (1983). Structure—activity relationships in chemoreception by human olfaction. Trends in Pharmacological Sciences, 4, 421-426. doi:10.1016/0165-6147(83)90475-3Fenko, A., Schifferstein, H. N. J., Huang, T.-C., & Hekkert, P. (2009). What makes products fresh: The smell or the colour? Food Quality and Preference, 20(5), 372-379. doi:10.1016/j.foodqual.2009.02.007Zarzo, M. (2012). What is a Fresh Scent in Perfumery? Perceptual Freshness is Correlated with Substantivity. Sensors, 13(1), 463-483. doi:10.3390/s130100463HARPER, R. (1975). SOME CHEMICALS REPRESENTING PARTICULAR ODOUR QUALITIES. Chemical Senses, 1(3), 353-357. doi:10.1093/chemse/1.3.353Fragancias del Mundo, SL. Murcia, Spain http://fragrancesoftheworld.esMilotic, D. (2003). The impact of fragrance on consumer choice. Journal of Consumer Behaviour, 3(2), 179-191. doi:10.1002/cb.131Lindqvist, A. (2012). Perfume Preferences and How They Are Related to Commercial Gender Classifications of Fragrances. Chemosensory Perception, 5(2), 197-204. doi:10.1007/s12078-012-9119-7Yokoyama, K., & Ebisawa, F. (1993). Detection and evaluation of fragrances by human reactions using a chemical sensor based on adsorbate detection. Analytical Chemistry, 65(6), 673-677. doi:10.1021/ac00054a00

Understanding the perceptual spectrum of commercial perfumes as a basis for a standard sensory wheel of fragrances

[EN] Given the enormous number of perfumes available on the market, it is of interest to guide consumers in their purchase of a new fragrance. One approach is to project the multidimensional perceptual space of scents on a two-dimensional sensory map based on meaningful dimensions. One of the pioneering studies on this issue mapped 94 commercial perfumes according to two axes. Such an odor map is discussed here in detail by applying Principal Component Analysis to the numeric odor description of 176 fragrances. Quantitative odor profiles were obtained from Fragrantica's website and three fragrances guides published by Haarmann & Reimer, Michael Edwards, and the French Society of Perfumers. A sensory map was obtained that reflected the similarities and dissimilarities between those odor descriptors most commonly used in perfumery. This representation was consistent with other related plots that have been previously reported. One dimension discriminated between fragrances targeted at men versus women. An orthogonal factor distinguished perfumes for daytime versus nighttime wear. These ratings, as well as seasonal preferences, could be estimated based on the main odor character attributes applied to describe the scent. The results provide a scientific basis for the comprehensive classification of commercial perfumes compiled by Edwards according to his famous "Fragrance Wheel".Zarzo Castelló, M. (2020). Understanding the perceptual spectrum of commercial perfumes as a basis for a standard sensory wheel of fragrances. Cosmetics. 7(3):1-21. https://doi.org/10.3390/cosmetics7010003S12173Eurofragrance 2011: Feminine Fragrances Genealogyhttp://www.eurofragance.com/docs/26_2011_fem_geneology_eurofragance.jpgOlfactive Families of Fragrances According to the French Society of Perfumershttps://www.parfumeurs-createurs.org/fr/filiere-parfum/les-familles-olfactives-102Osmoz Website for Olfactory Exploration of Men’s and Women’s Commercial Fragranceshttp://www.osmoz.com/perfumes/searchChastrette, M., Laumer, J.-Y. de S., & Sauvegrain, P. (1991). Analysis of a system of description of odors by means of four different multivariate statistical methods. Chemical Senses, 16(1), 81-93. doi:10.1093/chemse/16.1.81Milotic, D. (2003). The impact of fragrance on consumer choice. Journal of Consumer Behaviour, 3(2), 179-191. doi:10.1002/cb.131Cadoret, M., Lê, S., & Pagès, J. (2009). A Factorial Approach for Sorting Task data (FAST). Food Quality and Preference, 20(6), 410-417. doi:10.1016/j.foodqual.2009.02.010Veramendi, M., Herencia, P., & Ares, G. (2013). Perfume Odor Categorization: To What Extent Trained Assessors and Consumers Agree? Journal of Sensory Studies, 28(1), 76-89. doi:10.1111/joss.12025Kostov, B., Bécue-Bertaut, M., & Husson, F. (2014). An original methodology for the analysis and interpretation of word-count based methods: Multiple factor analysis for contingency tables complemented by consensual words. Food Quality and Preference, 32, 35-40. doi:10.1016/j.foodqual.2013.06.009Teixeira, M. A., Rodríguez, O., & Rodrigues, A. E. (2010). Perfumery Radar: A Predictive Tool for Perfume Family Classification. Industrial & Engineering Chemistry Research, 49(22), 11764-11777. doi:10.1021/ie101161vTeixeira, M. A., Barrault, L., Rodríguez, O., Carvalho, C. C., & Rodrigues, A. E. (2014). Perfumery Radar 2.0: A Step toward Fragrance Design and Classification. Industrial & Engineering Chemistry Research, 53(21), 8890-8912. doi:10.1021/ie403968wNotes on Scent. Cabinethttp://cabinetmagazine.org/issues/32/jasper_wagner.phpZarzo, M. (2012). What is a Fresh Scent in Perfumery? Perceptual Freshness is Correlated with Substantivity. Sensors, 13(1), 463-483. doi:10.3390/s130100463Zarzo, M., & Stanton, D. T. (2009). Understanding the underlying dimensions in perfumers’ odor perception space as a basis for developing meaningful odor maps. Attention, Perception & Psychophysics, 71(2), 225-247. doi:10.3758/app.71.2.225Zarzo, M. (2015). Underlying dimensions in the descriptive space of perfumery odors: Part II. Food Quality and Preference, 43, 79-87. doi:10.1016/j.foodqual.2015.02.018HARPER, R. (1975). SOME CHEMICALS REPRESENTING PARTICULAR ODOUR QUALITIES. Chemical Senses, 1(3), 353-357. doi:10.1093/chemse/1.3.353Fenko, A., Schifferstein, H. N. J., Huang, T.-C., & Hekkert, P. (2009). What makes products fresh: The smell or the colour? Food Quality and Preference, 20(5), 372-379. doi:10.1016/j.foodqual.2009.02.007Yokoyama, K., & Ebisawa, F. (1993). Detection and evaluation of fragrances by human reactions using a chemical sensor based on adsorbate detection. Analytical Chemistry, 65(6), 673-677. doi:10.1021/ac00054a004Higuchi, T., Shoji, K., & Hatayama, T. (2004). Multidimensional scaling of fragrances: A comparison between the verbal and non-verbal methods of classifying fragrances1. Japanese Psychological Research, 46(1), 10-19. doi:10.1111/j.1468-5884.2004.00232.xLindqvist, A. (2012). Perfume Preferences and How They Are Related to Commercial Gender Classifications of Fragrances. Chemosensory Perception, 5(2), 197-204. doi:10.1007/s12078-012-9119-

Symbolism of the pearls of the Holy Chalice of Valencia according to the Apocalypse

[ES] El Apocalipsis, que ha ejercido una notable influencia en el arte románico, podría haber inspirado el diseño del Santo Cáliz venerado en la catedral de Valencia, con 24 perlas engastadas en la base. Estas joyas parecen aludir a los 24 ancianos sentados alrededor del trono divino (Ap 4,4), los cuales simbolizan las doce tribus de Israel más las doce tribus del Cordero, es decir, los apóstoles. En la descripción de la nueva Jerusalén se menciona que ¿las doce puertas eran doce perlas¿ (Ap 21,21), las cuales han sido interpretadas por los exégetas clásicos como los apóstoles. Por otra parte, Ap 2,17 menciona ¿una piedrecita blanca¿ que podría aludir a una perla según Primasio (s. VI). Ésta podría considerarse como tésera o símbolo de las puertas de perla en la Jerusalén celeste. En definitiva, diversos indicios sugieren que la orfebrería del Santo Cáliz de Valencia fue cuidadosamente diseñada con fines catequéticos y no puramente estéticos.[EN] The Apocalypse, which has exerted a notable influence on Romanesque art, might have inspired the design of the Holy Chalice venerated at the Cathedral of Valencia, with 24 pearls mounted at the base. These jewels seem to allude to the 24 elders sitting around the divine throne (Rev 4:4), symbolizing the twelve tribes of Israel plus the twelve tribes of the Lamb, i.e., the apostles. In the description of the new Jerusalem it is mentioned that ¿the twelve gates were twelve pearls¿ (Rev 21:21), which have been interpreted by classical exegetes as the apostles. On the other hand, Rev 2:17 mentions ¿a white pebble¿ that could refer to a pearl according to Primasius (6th c.). It might be considered as token or symbol of the pearly gates at the heavenly Jerusalem. In short, several indications suggest that the metalwork decorating the Holy Chalice of Valencia was carefully designed for catechetical and not purely aesthetic purposes.Zarzo Castelló, M. (2020). Simbología de las perlas del Santo Cáliz de Valencia según el Apocalipsis. Cauriensia. 15:671-689. https://doi.org/10.17398/2340-4256.15.671S6716891

Simbología bíblica del Santo Cáliz de la Última Cena venerado en Valencia

[ES] La copa del Santo Cáliz que se venera en Valencia está tallada en piedra de ágata, alternándose bandas bastante traslúcidas, de escasa tonalidad, con otras que podrían describirse como de color sardio (es decir, rojo-amarronado). El sardio es la primera piedra del pectoral sacerdotal (Ex 28,16-21) asociada a Rubén, el primogénito de Jacob. Es muy simbólico que esta copa, supuestamente empleada por Jesús en la Última Cena según la tradición, se asemeje en cierto modo al sardio, pues Jesús es el unigénito de Dios. Por otra parte, esta copa evoca una llama de fuego cuando se ilumina desde dentro, lo cual es también muy figurativo en relación con la Eucaristía.[EN] The cup of the Holy Chalice venerated in Valencia is carved in agate stone, alternating quite translucent bands of low tone, with others that could be described as sardius color (i.e. red-brownish). Sardius is the first stone of the priestly breastplate (Ex 28,16-21) associated with Reuben, the first-born son of Jacob. It is very symbolic that this cup, supposed to have been used by Jesus at the Last Supper according to tradition, resembles in some way a sardius stone because Jesus is the only begotten son of God. On the other hand, this cup evokes a flame when illuminated from the inside, which is also very figurative in relation to the Eucharist.Zarzo Castelló, M. (2018). Simbología bíblica del Santo Cáliz de la Última Cena venerado en Valencia. Cauriensia. 13:529-556. https://doi.org/10.17398/2340-4256.13.529S5295561

Exegesis of the "sea of glass mingled with fire" (Rev. 15:2): possible interpretations as the eucharistic chalice

[EN] revelation 15:2 mentions ¿a kind of sea of glass mingled with fire¿. The expression ¿a kind of sea¿ suggests a figurative sense, perhaps in reference to the Sea of Bronze of the ancient Temple (1 Kings 7:24-25), a huge hemispherical water tank called sea in the Old Testament. When the Apocalypse was written, it was customary for Christian communities from Jewish tradition to celebrate the Eucharist with the Jewish blessing cup reserved for Easter, inherited from previous generations. These cups were often made of semiprecious stone and were shaped like a bowl, which might justify their analogy with the sea. Moreover, some were translucent and veined if carved in agate, onyx or sardonyx, as is the case of the Holy Chalice venerated at Valencia Cathedral or some chalices at St Mark¿s Basilica Museum in Venice. The sacred author might refer to a Eucharistic cup carved in stone in Rev 15:2, in relation to another ¿sea of glass¿ mentioned in Rev 4:6 that could allude to the baptismal font, and, as an antagonism to the ¿great winepress of God¿s wrath¿ (14:19).[ES] En Ap 15,2 se menciona "una especie de mar vítreo entreverado de fuego". La expresión "una especie de mar" sugiere un sentido figurado, quizás en alusión al Mar de bronce del antiguo Templo (1 R 7,23-25), enorme depósito de agua en forma semiesférica denominado en el Antiguo Testamento como mar. Cuando se escribió el Apocalipsis era habitual que las comunidades cristianas de tradición hebrea celebrasen la eucaristía con la copa de bendición judía reservada para Pascua, heredada de generaciones precedentes. Estas copas frecuentemente eran de piedra semipreciosa y tenían forma de cuenco, lo cual podría justificar su analogía con el mar. Además, en caso de estar talladas en ágata, ónice o sardónice, algunas eran traslúcidas y veteadas, como es el caso del Santo Cáliz venerado en la Catedral de Valencia o algunos cálices del museo de la Basílica de San Marcos en Venecia. El autor sagrado podría referirse en Ap 15,2 a una copa eucarística tallada en piedra, en relación con otro "mar vítreo" citado en Ap 4,6 que podría aludir a la pila bautismal, y como antagonismo a la "gran cuba de la ira de Dios" (14,19).Zarzo Castelló, M. (2018). Exégesis del "mar vítreo" entreverado de fuego" (Ap 15,2): posible interpretación como el cáliz eucarístico. Cuadernos de Teología. 10(2):290-326. https://doi.org/10.22199/S07198175.2018.0002.00004S29032610

Modeling the variability of solar radiation data among weather stations by means of principal components analysis

Measurements of global terrestrial solar radiation (R s) are commonly recorded in meteorological stations. Daily variability of R s has to be taken into account for the design of photovoltaic systems and energy efficient buildings. Principal components analysis (PCA) was applied to R s data recorded at 30 stations in the Mediterranean coast of Spain. Due to equipment failures and site operation problems, time series of R s often present data gaps or discontinuities. The PCA approach copes with this problem and allows estimation of present and past values by taking advantage of R s records from nearby stations. The gap infilling performance of this methodology is compared with neural networks and alternative conventional approaches. Four principal components explain 66% of the data variability with respect to the average trajectory (97% if non-centered values are considered). A new method based on principal components regression was also developed for R s estimation if previous measurements are not available. By means of multiple linear regression, it was found that the latent variables associated to the four relevant principal components can be fitted according to the latitude, longitude and altitude of the station where data were recorded from. Additional geographical or climatic variables did not increase the predictive goodness-of-fit. The resulting models allow the estimation of daily R s values at any location in the area under study and present higher accuracy than artificial neural networks and some conventional approaches considered. The proposed methodology for estimating R s based on geographical parameters would be of interest to design solar energy systems and to select their best location. © 2011 Elsevier Ltd.Zarzo Castelló, M.; Martí Pérez, PC. (2011). Modeling the variability of solar radiation data among weather stations by means of principal components analysis. Applied Energy. 88(8):2775-2784. doi:10.1016/j.apenergy.2011.01.070S2775278488

Multivariate time series analysis of temperatures in the archaeological museum of L'Almoina (Valencia, Spain)

[EN] An earlier study carried out in 2010 at the archaeological site of L'Almoina (Valencia, Spain) found marked daily fluctuations of temperature, especially in summer. Such pronounced gradient is due to the design of the museum, which includes a skylight as a ceiling, covering part of the remains in the museum. In this study, it was found that the thermal conditions are not homogeneous and vary at different points of the museum and along the year. According to the European Standard EN10829, it is necessary to define a plan for long-term monitoring, elaboration and study of the microclimatic data, in order to preserve the artifacts. With the aforementioned goal of extending the study and offering a tool to monitor the microclimate, a new statistical methodology is proposed. For this propose, during one year (October 2019-October 2020), a set of 27 data-loggers was installed, aimed at recording the temperature inside the museum. By applying principal component analysis and k-means, three different microclimates were established. In order to characterize the differences among the three zones, two statistical techniques were put forward. Firstly, Sparse Partial Least Squares Discriminant Analysis (sPLS-DA) was applied to a set of 671 variables extracted from the time series. The second approach consisted of using a random forest algorithm, based on the same functions and variables employed by the first methodology. Both approaches allowed the identification of the main variables that best explain the differences between zones. According to the results, it is possible to establish a representative subset of sensors recommended for the long-term monitoring of temperatures at the museum. The statistical approach proposed here is very effective for discriminant time series analysis and for explaining the differences in microclimate when a net of sensors is installed in historical buildings or museums.The authors are grateful to Angel Perles for his support in this research. In addition, the authors would like to thank the Museum of L'Almoina, managed by the local government of Valencia (Spain) and his director Vicent Escriva. Thanks are also given to Esther Nebot Diaz from the "Department of Conservation and Restoration of Cultural Heritage" of the Polytechnic University of Valencia (UPV) for her help in the calibration of sensors. S.R. wants to thank the grant received from Instituto Colombiano de Credito Educativo y Estudios Tecnicos en el Exterior (ICETEX) by means of Programa credito Pasaporte a la Ciencia ID 3595089, as well as by Pontificia Universidad Javeriana Cali (Nit 860013720-1) through the Convenio de Capacitacion para Docentes O. J. 086/17.Ramírez, S.; Zarzo Castelló, M.; García Diego, FJ. (2021). Multivariate time series analysis of temperatures in the archaeological museum of L'Almoina (Valencia, Spain). Sensors. 21(13):1-40. https://doi.org/10.3390/s21134377140211

A methodology for discriminant time series analysis applied to microclimate monitoring of fresco paintings

[EN] The famous Renaissance frescoes in Valencia¿s Cathedral (Spain) have been kept under confined temperature and relative humidity (RH) conditions for about 300 years, until the removal of the baroque vault covering them, carried out in 2006. In the interest of longer-term preservation and in order to maintain these frescoes in good condition, a unique monitoring system was implemented to record both air temperature and RH. Sensors were installed in different points at the vault of the apse, during the restoration process. The present study proposes a statistical methodology for analyzing a subset of RH data recorded in 2008 and 2010, from the sensors. This methodology is based on fitting different functions and models to the time series, in order to classify the sensors. The methodology proposed, computes classification variables and applies a discriminant technique to them. The classification variables correspond to estimates of parameters of the models and features such as mean and maximum, among others. These features are computed using values of the functions such as spectral density, sample autocorrelation (sample ACF), sample partial autocorrelation (sample PACF), and moving range (MR). The classification variables computed were structured as a matrix. Next, Sparse Partial Least Squares Discriminant Analysis (sPLS-DA) was applied in order to discriminate sensors according to their position in the vault. It was found that the classification of sensors derived from Seasonal ARIMA-TGARCH showed the best performance (i.e., lowest classification error rate). Based on these results, the methodology applied here can be useful for characterizing the differences in RH, measured at different positions in a historical building.This project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 814624. Furthermore, the project was partially supported by Instituto Colombiano de Credito Educativo y Estudios Tecnicos en el Exterior (ICETEX) by means of Programa credito Pasaporte a la Ciencia ID 3595089, and also by Pontificia Universidad Javeriana Cali (Nit 860013720-1) through the Convenio de Capacitacion para Docentes O. J. 086/17.Ramírez, S.; Zarzo Castelló, M.; Perles, A.; García Diego, FJ. (2021). A methodology for discriminant time series analysis applied to microclimate monitoring of fresco paintings. Sensors. 21(2):1-28. https://doi.org/10.3390/s21020436S12821

Characterization of temperature gradients according to height in a baroque church by means of wireless sensors

[EN] The baroque church of Saint Thomas and Saint Philip Neri (Valencia, Spain), which was built between 1727 and 1736, contains valuable paintings by renowned Spanish artists. Due to the considerable height of the central nave, the church can experience vertical temperature gradients. In order to investigate this issue, temperatures were recorded between August 2017 and February 2018 from a wireless monitoring system composed of 21 sensor nodes, which were located at different heights in the church from 2 to 13 m from the floor level. For characterizing the temperature at high, medium and low altitude heights, a novel methodology is proposed based on sparse Partial Least Squares regression (sPLS), Linear Discriminant Analysis (LDA), and the Holt-Winters method, among others, which were applied to a time series of temperature. This approach is helpful to discriminate temperature profiles according to sensor height. Once the vertical thermal gradients for each month were characterized, it was found that temperature reached the maximum correlation with sensor height in the period between August 10th and September 9th. Furthermore, the most important features from the time series that explain this correlation are the mean temperature and the mean of moving range. In the period mentioned, the vertical thermal gradient was estimated to be about 0.043 ºC/m, which implies a difference of 0.47 ºC on average between sensor nodes at 2 m from the floor with respect to the upper ones located at 13 m from the floor level. The gradient was estimated as the slope from a linear regression model using height and hourly mean temperature as the predictor and response, respectively. This gradient is consistent with similar reported studies. The fact that such gradient was only found in one month suggests that the mechanisms of dust deposition on walls involved in vertical thermal gradients are not important in this case regarding the preventive conservation of artworks. Furthermore, the methodology proposed here was useful to discriminate the time series at high, medium and low altitude levels. This approach can be useful when a set of sensors is installed for microclimate monitoring in churches, cathedrals, and other historical buildings, at different levels and positions.This project received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 814624.Ramírez, S.; Zarzo Castelló, M.; Perles, A.; García Diego, FJ. (2021). Characterization of temperature gradients according to height in a baroque church by means of wireless sensors. Sensors. 21(20):1-35. https://doi.org/10.3390/s21206921S135212