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Transmittance of water vapour, aerosols and Rayleigh scattering in the spectral region 700-1000 nm, calculated using MODTRAN set at 0.1 nm resolution, at SZA = 0 • IWV = 1 cm, IWV = 2 cm and AOD = 0.1 and AOD = 0.2 at 700 nm using an Ångström exponent of 1.5. Black vertical dotted lines represent WMO recommendations for IWV retrieval.
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The Precision Solar Spectroradiometer (PSR) is a new spectroradiometer developed at Physikalisch-Meteorologisches Observatorium Davos – World Radiation Center (PMOD–WRC), Davos, measuring direct solar irradiance at the surface, in the 300–1020 nm spectral range and at high temporal resolution. The purpose of this work is to investigate the instrume...
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... the near-infrared measuring spectral region of PSR the most important water absorption has been found in the 700- 1000 nm wavelength region. Figure 2 shows the transmit- tance from Rayleigh scattering, aerosols and IWV, as cal- culated by the MODerate resolution atmospheric TRANs- misson radiative transfer model (MODTRAN RTM) (Berk et al., 1987(Berk et al., , 1999). Aerosols direct effect on irradiance is measured through AOD, which is the integrated extinction coefficient on vertical column due to aerosols. ...
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... misson radiative transfer model (MODTRAN RTM) (Berk et al., 1987(Berk et al., , 1999). Aerosols direct effect on irradiance is measured through AOD, which is the integrated extinction coefficient on vertical column due to aerosols. Spectral vari- ation of AOD at different wavelengths is measured through Ångström exponent. For the example in Fig. 2, Ångström ex- ponent equal to 1.5 was considered and aerosol of AOD 0.1 and 0.2. Inclination of aerosol transmittance lines is propor- tional to Ångström exponent and higher AOD will lead to lower absolute values. WMO (2005) recommends 719, 817 and 946 nm central wavelengths to retrieve IWV, which ap- pears as significant drops in the ...
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... equal to 1.5 was considered and aerosol of AOD 0.1 and 0.2. Inclination of aerosol transmittance lines is propor- tional to Ångström exponent and higher AOD will lead to lower absolute values. WMO (2005) recommends 719, 817 and 946 nm central wavelengths to retrieve IWV, which ap- pears as significant drops in the solar transmittance spectra in Fig. 2. Ingold et al. (2000) investigated the quality of the retrievals at these wavelengths and found that the one at 946 nm is the most robust, which could be translated as the wavelength range with the strongest absorption of ...
Citations
... More details for the technical characteristics of the PSR can be found in [27]. The PSR has been used for solar measurements but also for retrievals of atmospheric parameters such as columnar water vapor [28] and AOD [29]. ...
Energy nowcasting is a valuable asset in managing energy loads and having real-time information on solar irradiation availability. In this study, we evaluate the spectrally integrated outputs of the SENSE system for solar irradiance nowcasting for the period of the ASPIRE (atmospheric parameters affecting spectral solar irradiance and solar energy) campaign (December 2020–December 2021) held in Athens, Greece. For the needs of the campaign, several ground-based instruments were operating, including two pyranometers, a pyrheliometer, a cloud camera, a CIMEL sunphotometer, and a precision spectral radiometer (PSR). Global horizontal irradiance (GHI) estimations were more accurate than direct normal irradiance (DNI). SENSE estimations are provided every 15 min, but when comparing bigger time intervals (hours-days), the statistics improved. A dedicated assessment of the SENSE’s inputs is performed in respect to ground-based retrievals, considering cloud conditions (from a sky imager), AOD, and precipitable water vapor from AERONET. The factor that established the larger errors was the visibility of the solar disc, which cannot be defined by the available sources of model inputs. Additionally, there were discrepancies between the satellite estimation of the clouds and the ground picture, which caused deviations in results. AOD differences affected more the DNI.
... Further details on the application of spectroradiometers to PV technology are provided in Section S1 of the Supplementary Materials. Array spectroradiometers are also adopted in studies about air quality, photochemistry and atmospheric composition [12][13][14][15][16][17][18][19][20][21], by taking advantage of the spectral signature of some light-absorbing atmospheric compounds; phototherapy and medical dosimetry [22,23], in which the observation of the radiation spectrum is essential for assessing wavelengthdependent biological effects; measurement of the Earth's surface reflectance, e.g., to identify snow impurities [24]; and the monitoring of water quality and ecosystems [25][26][27]. Finally, array systems are not only useful in research but may also be introduced in industrial applications where reference solar spectra are required [28] or where spectroscopy-based techniques are employed for process control [29]. ...
Array spectroradiometers are increasingly being used to measure natural and artificial optical radiation because of their many advantages compared to traditional instruments. This study aims to thoroughly characterise a commercially available, cost-effective array device (AvaSpec ULS2048-LTEC) and compare its measurements of global solar irradiance in the 290–1100 nm wavelength range with those collected during three short-term field campaigns from more advanced, or specifically designed instruments. Moreover, the AvaSpec observations were compared with the output of a radiative transfer model. The results show that, despite its conceptually simple instrumental design, the AvaSpec can provide measurements of nearly comparable quality to those from reference instruments (e.g., UV index and global horizontal irradiance generally within ±5%) if all corrections are performed. These preliminary observations will be the basis of a long-term series at the Aosta–Saint-Christophe observatory, which can be employed to study solar energy production, biological effects and atmospheric composition changes in the Alpine environment. All procedures, including the encountered issues and proposed solutions, are described in detail.
... for AOD at visible and near-infrared wavelengths compared to CE-318. The PWV given by the monochromatic method around 940 nm has great variability at different wavelengths (Kazadzis et al., 2018a(Kazadzis et al., , b, 2014Raptis et al., 2018). García-Cabrera et al. (2020) and García et al. (2021) retrieved PWV and AOD using the EKO MS711 spectroradiometer at the Izana Observatory in Spain and compared them with CE-318, showing that PWV has a mean bias of 0.033 cm and the AOD is broadly in line. ...
Based on the strict radiative transfer algorithm, a new method is developed to derive the precipitable water vapor (PWV) and aerosol optical depth (AOD) from the ground-based direct sun irradiance measurements. The attenuated direct irradiance from 300 to 1700 nm was measured by a pair of grating spectroradiometers, MS711 and MS712 produced by EKO Instruments, located at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing (39.98∘ N, 116.38∘ E), from June 2020 to March 2021. Compared with regular sun photometers such as CE-318 and POM, EKO instruments can measure a wider range of continuous spectra, but their field of view (FOV) is also relatively large. In the PWV inversion of this work, a strong water vapor absorption band around 1370 nm is introduced to retrieve PWV in a relatively dry atmosphere. The circumsolar radiation (CSR) of the EKO instruments is corrected to reduce the influence of scattering from a relatively larger FOV on the AOD inversion. The PWV and AOD inversion results obtained by MS711 and MS712 are compared with the synchronous data of the CE-318 sun photometer. The two retrieval results are highly consistent. The correlation coefficient, mean bias, and standard deviation of PWVEKO and PWVCIMEL are 0.999, −0.027 cm (−2.42 %), and 0.054 cm (3.93 %), respectively, and the relative deviations of the differences between the two are slightly larger for drier air (PWV < 0.5 cm) and lower solar elevation angle. The correlation coefficients of AODEKO and AODCIMEL at 380, 440, 500, 675, 870, and 1020 nm are greater than 0.99, and the relative deviations vary between −6.59 % and 4.27 %.
... The Precision Solar Spectroradiometer has been designed and manufactured by Physicalisch-Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC), Davos, Switzerland, for high precision and accuracy of solar spectral measurements. It measures irradiance at 1024 channels in the spectral range of 300-1020 nm with an average Atmosphere 2021, 12, 145 4 of 16 step of~0.7 nm, spectral resolution in the range of 1.5-6 nm (depending on the measured wavelength) [40,41]. PSR 007 is installed in Athens (37.9 N, 23.7 E, 130 m above sea level) and it was last calibrated on June 2019 at the World Radiation Center using a calibrated standard 1000 W tungsten-halogen FEL lamp. ...
... The lowest mean ratio is observed at 60 • , which is 0.94. The most variable spectral ratios are reported in the region below 305 nm, where the measured PSR irradiances are very low, including the highest uncertainties [41,42]. In this area, average ratios are from 0.76 (SZA = 60 • ) to 1.12 (SZA = 30 • ) with a σ = 0.23. ...
... This mean agreement of ~2% shows the relatively accurate use of the model inputs that simulate very well the synchronous measurements The lowest mean ratio is observed at 60°, which is 0.94. The most variable spectral ratios are reported in the region below 305 nm, where the measured PSR irradiances are very low, including the highest uncertainties [41,42]. In this area, average ratios are from 0.76 (SZA = 60°) to 1.12 (SZA = 30°) with a σ = 0.23. Figure 6. ...
In this study we focus on measurements and modeled UV index in the region of Athens, Greece, during a low ozone event. During the period of 12–19 May 2020, total ozone column (TOC) showed extremely low values, 35–55 Dobson Units (up to 15%) decrease from the climatic mean (being lower than the −2σ). This condition favors the increase of UV erythemal irradiance, since stratospheric ozone is the most important attenuator at the UVB spectral region. Simultaneously, an intrusion of Saharan dust aerosols in the region has masked a large part of the low ozone effect on UV irradiance. In order to investigate the event, we have used spectral solar irradiance measurements from the Precision Solar Radiometer (PSR), TOC from the Brewer spectrophotometer, and Radiative Transfer Model (RTM) calculations. Model calculations of the UV Index (UVI) showed an increase of ~30% compared to the long-term normal UVI due to the low TOC while at the same time and for particular days, aerosols masked this effect by ~20%. The RTM has been used to investigate the response in the UV spectral region of these variations at different solar zenith angles (SZAs). Spectra simulated with the RTM have been compared to measured ones and an average difference of ~2% was found. The study points out the importance of accurate measurements or forecasts of both ozone and aerosols when deriving UVI under unusual low ozone–high aerosol conditions.
... More sophisticated PWV solar devices are spectrometers operating in the infrared domain such as those based on the Fourier Transform Infrared (FTIR) technique, which provide precise water vapor profiles and integrated PWV amounts by analyzing the measured high-resolution solar absorption spectra (e.g., [25][26][27]). In the visible and near infrared spectral range, PWV data can be also retrieved from direct irradiance measured by spectroradiometers, but the works on this matter are scarce (e.g., [28][29][30]). The first studies date from the beginning of the 20th century when a method to derive the PWV by spectroscopy was described [31] and later applied at Mount Wilson, California to retrieve the PWV [32]. ...
... The first studies date from the beginning of the 20th century when a method to derive the PWV by spectroscopy was described [31] and later applied at Mount Wilson, California to retrieve the PWV [32]. Since then, several retrieval methodologies have been proposed to retrieve PWV from solar absorption spectra, including monochromatic approaches, spectral windows, differential optical absorption spectroscopy (DOAS), and iterative nonlinear fitting models (e.g., [10][11][12][13]29,30]). ...
... In preliminary analysis of this study, the approach of [30] was used, obtaining PWV retrievals very similar (not shown here) to those obtained with the approximation indicated below. Since the moderate resolution of the EKO MS-711 spectroradiometer (10 nm) in the spectral range in which the PWV is retrieved, we decided to choose a more robust method in which the whole spectral range in which the water vapor absorbs significantly is used, to minimize the signal-to-noise ratio. ...
Precipitable water vapor retrievals are of major importance for assessing and understanding atmospheric radiative balance and solar radiation resources. On that basis, this study presents the first PWV values measured with a novel EKO MS-711 grating spectroradiometer from direct normal irradiance in the spectral range between 930 and 960 nm at the Izaña Observatory (IZO, Spain) between April and December 2019. The expanded uncertainty of PWV (UPWV) was theoretically evaluated using the Monte-Carlo method, obtaining an averaged value of 0.37 ± 0.11 mm. The estimated uncertainty presents a clear dependence on PWV. For PWV ≤ 5 mm (62% of the data), the mean UPWV is 0.31 ± 0.07 mm, while for PWV > 5 mm (38% of the data) is 0.47 ± 0.08 mm. In addition, the EKO PWV retrievals were comprehensively compared against the PWV measurements from several reference techniques available at IZO, including meteorological radiosondes, Global Navigation Satellite System (GNSS), CIMEL-AERONET sun photometer and Fourier Transform Infrared spectrometry (FTIR). The EKO PWV values closely align with the above mentioned different techniques, providing a mean bias and standard deviation of −0.30 ± 0.89 mm, 0.02 ± 0.68 mm, −0.57 ± 0.68 mm, and 0.33 ± 0.59 mm, with respect to the RS92, GNSS, FTIR and CIMEL-AERONET, respectively. According to the theoretical analysis, MB decreases when comparing values for PWV > 5 mm, leading to a PWV MB between −0.45 mm (EKO vs. FTIR), and 0.11 mm (EKO vs. CIMEL-AERONET). These results confirm that the EKO MS-711 spectroradiometer is precise enough to provide reliable PWV data on a routine basis and, as a result, can complement existing ground-based PWV observations. The implementation of PWV measurements in a spectroradiometer increases the capabilities of these types of instruments to simultaneously obtain key parameters used in certain applications such as monitoring solar power plants performance.
... PWV can be monitored with high precision through microwave radiometer profilers (MWPs) [11], the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) correction algorithm for the Vaisala RS92 radiosondes (GRUAN RS92) [12] or ground-based Fourier Transform Infrared (FTIR) spectrometers [13]. Less precise devices for PWV monitoring such as Vaisala RS92 [14] and RS41 [15] radiosondes, Global Navigation Satellite System (GNSS) receivers [16][17][18], sun/moon/star photometers [19][20][21][22][23] or spectroradiometers [24,25] allow us to expand the spatial coverage of the PWV measurements, but with a lower precision, ranging from 7% to 20% and decreasing under dry conditions [13]. ...
The study shows the first results of the column-integrated water vapor retrieved by the new ZEN-R52 radiometer. This new radiometer has been specifically designed to monitor aerosols and atmospheric water vapor with a high degree of autonomy and robustness in order to allow the expansion of the observations of these parameters to remote desert areas from ground-based platforms. The ZEN-R52 device shows substantial improvements compared to the previous ZEN-R41 prototype: a smaller field of view, an increased signal-to-noise ratio, better stray light rejection, and an additional channel (940 nm) for precipitable water vapor (PWV) retrieval. PWV is inferred from the ZEN-R52 Zenith Sky Radiance (ZSR) measurements using a lookup table (LUT) methodology. The improvement of the new ZEN-R52 in terms of ZSR was verified by means of a comparison with the ZEN-R41, and with the Aerosol Robotic Network (AERONET) Cimel CE318 (CE318-AERONET) at Izaña Observatory, a Global Atmosphere Watch (GAW) high mountain station (Tenerife, Canary Islands, Spain), over a 10-month period (August 2017 to June 2018). ZEN-R52 aerosol optical depth (AOD) was extracted by means of the ZEN–AOD–LUT method with an uncertainty of ±0.01 ± 0.13*AOD. ZEN-R52 PWV extracted using a new LUT technique was compared with quasi-simultaneous (±30 s) Fourier Transform Infrared (FTIR) spectrometer measurements as reference. A good agreement was found between the two instruments (PWV means a relative difference of 9.1% and an uncertainty of ±0.089 cm or ±0.036 + 0.061*PWV for PWV <1 cm). This comparison analysis was extended using two PWV datasets from the same CE318 reference instrument at Izaña Observatory: one obtained from AERONET (CE318-AERONET), and another one using a specific calibration of the 940-nm channel performed in this work at Izaña Atmospheric Research Center Observatory (CE318-IARC), which improves the PWV product.
... receiver considering satellite precise orbits at IZO (Romero Campos et al., 2009), A H 2 O the spectral absorption coefficient Rothman et al. (2013), and the b exponent depends on the central wavelength position, instrument filter function, as well as the atmosphere pressure and temperature (Halthore et al., 1997). We have determined τ H 2O (λ) from the transmittance for different water vapour and solar zenith angle (SZA) values from the MODTRAN model (Raptis et al., 2018). ...
Abstract. Spectral direct UV-Visible normal solar irradiance (DNI) measured with an EKO MS-711 spectroradiometer at the Izaña Atmospheric Observatory (IZO, Spain) has been used to determine aerosol optical depth (AOD) at several wavelengths (340, 380, 440, 500, 675 and 870 nm) between April and September 2019 that have been compared with synchronous AOD measurements from a reference Cimel-AERONET (Aerosol RObotic NETwork) sunphotometer. The EKO MS-711 has been calibrated at Izaña Observatory using the Langley-Plot method during the study period. Although this instrument has been designed for spectral solar DNI measurements, and therefore has a field of view (FOV) of 5° that is twice that recommended in solar photometry for AOD determination, the AOD differences compared against the AERONET Cimel reference instrument (FOV ∼ 1.2°), are fairly small. The comparison results between AOD Cimel and EKO MS-711 present a root mean square (RMS) of 0.013 (24.6 %) at 340, and 380 nm, and 0.029 (19.5 %) for longer wavelengths (440, 500, 675 and 870 nm). However, under relatively high AOD, near forward aerosol scattering might be significant because of the relatively large circumsolar radiation (CSR) due to the large EKO MS-711 FOV, resulting in a small but significant AOD underestimation in the UV range. The AOD differences decrease considerably when CSR corrections, estimated from LibRadtran radiative transfer model simulations, are performed, obtaining RMS of 0.006 (14.9 %) at 340 and 380 nm, and 0.005 (11.1 %) for longer wavelengths. The percentage of 2-minute synchronous EKO AOD–Cimel AOD differences within the World Meteorological Organization (WMO) traceability limits were ≥ 96 % at 500 nm, 675 nm and 870 nm with no CSR corrections. After applying the CSR corrections, the percentage of AOD differences within the WMO traceability limits increased to > 95 % for 380, 440, 500, 675 and 870 nm, while for 340 nm the percentage of AOD differences showed a poorer increase from 67 % to a modest 86 %.
In August 2021, a historic heatwave was recorded in Greece which resulted in extreme wildfire events that strongly affected the air quality over the city of Athens. Saharan dust was also transferred over Greece in the same period due to the prevailing southern winds. The impact of these events on air quality and surface solar radiation are investigated in this study. Event characterization based on active and passive remote sensing instrumentation has been performed. The study shows that significantly increased levels of air pollution were recorded during the end of July/first week of August. The smoke led to unusually high AOD values (up to 3.6), high Ångström Exponent (AE) (up to 2.4) and a strong and negative dependence of single scattering albedo (SSA) on wavelength that was observed to decrease from 0.93 at 440 nm to 0.86 at 1020 nm signifying the presence of strong absorbing aerosols. While, the dust event led to high AOD (up to 1.4), low AE (up to 0.9) and positive dependence of SSA on wavelength that was observed to increase from 0.89 at 440 nm to 0.95 at 1020 nm indicating large forward scattering due to coarse particles. Furthermore, the analysis of the smoke aerosol optical properties during the transfer from the source to a distance of about 240 km revealed that the SSA and AE changed significantly during the transfer, which lasted approximately 9 h. The transport of the plume led to an impressive change in the spectral shape of SSA whose value significantly increased pointing to the aging of smoke and the dilution of plumes while the transport. The impact of dust and smoke on spectral solar irradiance reveals significant differences in the spectral shape of attenuation caused by the two different aerosol species. The attenuation of solar irradiance in UV-B irradiance was found to be least in case of dust and highest due to smoke (up to 60 % or more) and intermediate in the case of a mixture of smoke and dust. The attenuation was comparatively less in NIR region (mostly within 20 % but it even reached up to 40 % in the presence of smoke) and VIS region (but greater than NIR region). Also, the AOD variations from climatology led to decrease in UV Index up to 53 %, in vitamin-D up to 50 %, in photosynthetically active radiation up to 21 % and in GHI up to 17 %, with implications on health, agriculture and energy. This study highlights the wider impacts of wildfires that are part of the wider problem of the Mediterranean countries, whose frequency is predicted to increase in view of the projected increasing occurrence of summer heatwaves.
Spectral direct UV–visible normal solar irradiance (DNI) has been measured with an EKO MS-711 grating spectroradiometer, which has a spectral range of 300–1100 nm, and 0.4 nm step, at the Izaña Atmospheric Observatory (IZO, Spain). It has been used to determine aerosol optical depth (AOD) at several wavelengths (340, 380, 440, 500, 675, and 870 nm) between April and September 2019, which has been compared with synchronous AOD measurements from a reference Cimel and Aerosol RObotic NETwork (AERONET) sun photometer. The EKO MS-711 has been calibrated at the Izaña Atmospheric Observatory by using the Langley plot method during the study period. Although this instrument has been designed for spectral solar DNI measurements, and therefore has a field of view (FOV) of 5∘ that is twice the recommended amount in solar photometry for AOD determination, the AOD differences compared to the AERONET–Cimel reference instrument (FOV ∼1.2∘) are fairly small. A comparison of the results from the Cimel AOD and EKO MS-711 AOD presents a root mean square (rms) of 0.013 (24.6 %) at 340 and 380 nm, and 0.029 (19.5 %) for longer wavelengths (440, 500, 675, and 870 nm). However, under relatively high AOD, near-forward aerosol scattering might be significant because of the relatively large circumsolar radiation (CSR) due to the large EKO MS-711 FOV, which results in a small but significant AOD underestimation in the UV range. The AOD differences decrease considerably when CSR corrections, estimated from libRadtran radiative transfer model simulations, are performed and obtain an rms of 0.006 (14.9 %) at 340 and 380 nm, and 0.005 (11.1 %) for longer wavelengths. The percentage of 2 min synchronous EKO AOD–Cimel AOD differences within the World Meteorological Organization (WMO) traceability limits were ≥96 % at 500, 675, and 870 nm with no CSR corrections. After applying the CSR corrections, the percentage of AOD differences within the WMO traceability limits increased to >95 % for 380, 440, 500, 675, and 870 nm, while for 340 nm the percentage of AOD differences showed a poorer increase from 67 % to a modest 86 %.
A precision solar spectroradiometer (PSR) has been designed for high precision and accurate measurements of direct normal spectral solar irradiance in the wavelength range 300–1000 nm. Each PSR is radiometrically characterised and calibrated in the optical laboratory of PMOD/WRC. The calibration is traceable to SI through the primary spectral irradiance standard of the Physikalisch-Technische Bundesansalt (PTB), in Braunschweig, Germany. The expanded relative uncertainty for spectral solar irradiance measurements in the 350–1000 nm range is between 1.7% and 2.0%, with larger uncertainties below 400 nm which are mainly caused by the low signal levels and the uncertainties due to the straylight correction. A solar extraterrestrial spectrum was retrieved from solar measurements using the Langley-technique at a high altitude observatory and was found to be in excellent agreement with a literature solar spectrum (mean ratio 0.998±0.019). On two clear sky days solar measurements from 3 PSR and one independently calibrated spectroradiometer deployed during the International Pyrheliometer Comparison agreed to within their combined expanded uncertainties of 3%. Aerosol optical depth retrieved from the same solar measurements of the three PSR showed median differences with respect to the World reference for AOD between −0.010 and +0.014 at the center wavelengths 368 nm, 412 nm, 500 nm, and 862 nm. The instrument has a second auxiliary port for connecting different entrance optics for near coincident measurements such as global solar irradiance.
