Improved diffusers for solar UV spectroradiometers

Pulli, Tomi; Kärhä, Petri; Mes, J.; Schreder, Josef; Jaanson, Priit; Manoocheri, Farshid

doi:10.1063/1.4804894

Cited by 4 publications

(5 citation statements)

References 7 publications

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“…For UV-C angles of incidence ≤75°, we predicted analytically and measured an integrated cosine error of 2.7% and 0.97%, respectively. Both the analytical and empirical integrated cosine errors of the PCI-PTFE stack are smaller in magnitude than observed for the PCI-borosilicate stack, as anticipated, and are lower than others have measured for 0.5 mm-thick PTFE 33,40 . We hypothesize that the lower integrated cosine error observed here could arise from differing limits of integration.…”

Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...supporting

confidence: 74%

“…We hypothesize that the lower integrated cosine error observed here could arise from differing limits of integration. Due to the limited number of angles of incidence characterized empirically, we integrate through 75°, while others 33,40 integrate through 85° (past the ISO/CIE 19476 definition 32 ), incorporating contributions from an additional 10° over which cosine error is typically large. At each rotation angle measured except 90°, PCI-PTFE angular response was within error of the ideal response (Figure 2F), suggesting a near-ideal angular response.…”

Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...mentioning

confidence: 99%

“…We hypothesize that the empirical angular response of the PCI-PTFE stack was closer to ideal due to some surface diffuser behavior at the interface (not incorporated in the model), and/or slight curvature or non-negligible spacing between the deformable PTFE and PCI. Diffuser-sensor spacing and diffuser curvature have been shown to substantially alter the angular response of radiometers [40][41][42] .…”

Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...mentioning

confidence: 99%

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Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet‐C Dosimeters

Geldert

Grist

Herr

2021

Photochem & Photobiology

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A challenge for sensors used in ultraviolet-C (UV-C) decontamination protocols of N95 respirators is validation that the entire N95 surface receives the minimum acceptable dose. Photochromic indicators (PCIs) can accurately measure UV-C dose on nonplanar surfaces, but often saturate below doses required to decontaminate porous, multilayered textiles such as N95s. Here, we investigate the use of optical attenuators to extend PCI dynamic range while maintaining a nearideal angular response -critical for accurate measurements when UV-C is uncollimated. Through an analytical model, we show that tuning attenuator refractive index, attenuation coefficient, and thickness can extend dynamic range, but compromises ideal angular response unless the attenuator is an ideal diffuser. To demonstrate this tradeoff empirically, we pair PCIs with model specular (floated borosilicate) and diffuse (polytetrafluoroethylene) attenuators, characterize the angular response, and evaluate on-N95 UV-C dose measurement accuracy of each PCI-attenuator stack in a UV-C decontamination system. While both borosilicate and polytetrafluoroethylene increase PCI dynamic range >4×, both attenuators introduce angle-dependent transmittance, which causes location-dependent underestimation of UV-C dose. The PCI-borosilicate and PCIpolytetrafluoroethylene stacks underreport true on-N95 dose by 1) 14.7% and 3.6%, respectively, on a surface near-normal to the array of source lamps, and 2) 40.8% and 19.8%, respectively, on a steeply sloped location. Overall, we demonstrate that while planar optical attenuators can increase PCI dynamic range, verification of near-ideal angular response is critical for accurate UV-C dose measurement.

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Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...supporting

confidence: 74%

Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...mentioning

confidence: 99%

Section: Diffuse Attenuators Cause Less Deviation From Ideal Angular ...mentioning

confidence: 99%

See 1 more Smart Citation

Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet‐C Dosimeters

Geldert

Grist

Herr

2021

Photochem & Photobiology

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“…The concern increased even more after ozone loss occurrences were also observed at middle latitudes which in turn affect solar UV levels at the ground (Kerr and McElroy, 1993;Zerefos et al, 1995;Herman et al, 1996;Petkov et al, 2014). The apparent increase in UV-B irradiance led to the development and deployment of a large number of instruments performing spectral or broadband measurements of the UV-B irradiance, as well as quantities directly linked to biological effects of the UV radiation such as the am-bient erythemal irradiance (Booth et al, 1994;Gröbner et al, 2006;Schmalwieser et al, 2017). Since the 1980s, improved spectral sensors (compared to those deployed in the 1980s) have been developed, providing more accurate measurements in a wider range of wavelengths extending up to the visible region (e.g.…”

Section: Introductionmentioning

confidence: 99%

Monitoring of solar spectral ultraviolet irradiance in Aosta, Italy

Fountoulakis

Diémoz

Siani

et al. 2020

Earth Syst. Sci. Data

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Abstract. A Bentham DTMc300 spectroradiometer is deployed at the station of Aosta–Saint-Christophe, Italy, at the headquarters of the Regional Environmental Protection Agency (ARPA) and has been performing continuous high-quality spectral measurements of the solar ultraviolet (UV) irradiance since 2006. The measuring site is located in the north-western region of the Alps, on a large valley floor at the altitude of 570 m a.s.l., surrounded by mountains. It is very significant to have accurate measurements in such a sensitive environment, since the complex terrain and the strongly variable meteo-climatic conditions typical of the Alps induce large spatial and temporal variability in the surface levels of the solar UV irradiance. The spectroradiometer is also used as a reference of a regional UV network, with additional stations located at different altitudes (1640 and 3500 m a.s.l.) and environmental conditions (mountain and glacier). In the present study we discuss the procedures and the technical aspects which ensure the high quality of the measurements performed by the reference instrument and the procedures used to characterize the Bentham. The quality control and quality assurance (QA–QC) procedures are also discussed. We show that the good quality of the spectral measurements is further ensured by a strong traceability chain to the irradiance scale of the Physikalisch-Technische Bundesanstalt (PTB) and a strict calibration protocol. Recently, the spectral UV dataset of Aosta–Saint-Christophe has been re-evaluated and homogenized. The final spectra constitute one of the most accurate datasets globally. At wavelengths above 310 nm and for solar zenith angles below 75∘, the expanded (k=2) uncertainty in the final dataset decreases with time, from 7 % in 2006 to 4 % in the present. The present study not only serves as the reference document for any future use of the data, but also provides useful information for experiments and novel techniques which have been applied for the characterization of the instrument and the QA–QC of the spectral UV measurements. Furthermore, the study clearly shows that maintaining a strong traceability chain to a reference scale of spectral irradiance is critical for the good quality of the measurements. The studied spectral dataset is freely accessible at https://doi.org/10.5281/zenodo.4028907 (Fountoulakis et al., 2020b).

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“…Garane et al (2006) estimated the expanded uncertainty in the measurements of two Brewer spectrophotometers, with a single and a double monochromator, to 13% and 10% respectively for SZAs below 75° and wavelengths below 305 nm. However, significant progress has been achieved in the past two decades regarding the methods used for the instrument calibration and characterization, and the quality assurance and quality control (QA/QC) procedures (Fountoulakis et al, 2016;Fountoulakis et al, 2017;Gröbner et al, 2010;Hülsen et al, 2016;Lakkala et al, 2018;Lakkala et al, 2008), which in conjunction to the improvement of the technical characteristics of the instruments (Gröbner, 2003;Pulli et al, 2013) allows spectral measurements with expanded uncertainty of ~2% for wavelengths above 310 nm (Hülsen et al, 2016). Low uncertainty measurements are necessary for the detection of trends in the levels of solar UV irradiance (Bernhard, 2011;Seckmeyer et al, 2009;Weatherhead et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Monitoring of solar spectral ultraviolet irradiance in Aosta, Italy

Fountoulakis¹,

Diémoz²,

Siani³

et al. 2020

Preprint

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Abstract. A Bentham DTMc300 spectrophotometer is deployed at the station of Aosta–Saint-Christophe, Italy, at the headquarters of the Regional Environmental Protection Agency (ARPA) and performs continuous high quality spectral measurements of the solar ultraviolet (UV) irradiance since 2006. The measuring site is located in the North-western of the Alps, in a large valley floor at the altitude of 570 m a.s.l., surrounded by mountains. It is very significant to have accurate measurements in such a sensitive environment, since the complex terrain and the strongly variable meteo-climatic conditions typical of the Alps induce large spatial and temporal variability in the surface levels of the solar UV irradiance. The spectroradiometer is moreover used as a reference of a regional UV network, with additional stations located at different altitudes (1640 and 3500 m a.s.l.) and environmental conditions (mountain and glacier). In the present study we discuss the procedures and the technical aspects which ensure the high quality of the measurements performed by the reference instrument, and subsequently of the entire network. In particular, we describe the procedures used to characterize the Bentham for its characteristics which affect the quality of the measurements. The used Quality Control/Quality Assurance (QA/QC) procedures are also discussed. We show that the good quality of the spectral measurements is further ensured by a strong traceability chain to the world reference QASUME and a strict calibration protocol. Recently, the spectral UV dataset of Aosta–Saint-Christophe has been re-evaluated and homogenized. The final spectra consist one of the most accurate datasets globally. At wavelengths above 310 nm and for solar zenith angles below 75° the expanded uncertainty in the final dataset decreases with time, from 7 % in 2006 to 4 % in the present. The present study not only serves as the reference document for any future use of the data, but also provides useful information for experiments and novel techniques which have been applied for the characterization of the instrument, and the QA/QC of the spectral UV measurements. Furthermore, the study clearly shows that maintaining a strong traceability chain to a reference instrument is critical for the good quality of the measurements. The studied spectral dataset is freely accessible at https://doi.org/10.5281/zenodo.3934324 (Fountoulakis et al., 2020).

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Improved diffusers for solar UV spectroradiometers

Cited by 4 publications

References 7 publications

Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet‐C Dosimeters

Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet‐C Dosimeters

Monitoring of solar spectral ultraviolet irradiance in Aosta, Italy

Monitoring of solar spectral ultraviolet irradiance in Aosta, Italy

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