Examinando por Autor "Serrano, Antonio"

Mostrando 1 - 4 de 4

Acceso Abierto
Comparison of global UV spectral irradiance measurements between a BTS CCD-array and a Brewer spectroradiometer
(European Geosciences Union, 2022-07-15) González, Carmen; Vilaplana, Jose Manuel; Bogeat Sánchez-Piqueras, José Antonio; Serrano, Antonio
Spectral measurements of UV irradiance are of great importance for protecting human health as well as for supporting scientific research. To perform these measurements, double monochromator scanning spectroradiometers are the preferred devices thanks to their linearity and stray-light reduction. However, because of their high cost and demanding maintenance, CCD-array-based spectroradiometers are increasingly used for monitoring UV irradiance. Nevertheless, CCD-array spectroradiometers have specific limitations, such as a high detection threshold or stray-light contamination. To overcome these challenges, several manufacturers are striving to develop improved instrumentation. In particular, Gigahertz-Optik GmbH has developed the stray-light-reduced BTS2048-UV-S spectroradiometer series (hereafter “BTS”). In this study, the long-term performance of the BTS and its seasonal behavior, regarding global UV irradiance, was assessed. To carry out the analysis, BTS irradiance measurements were compared against measurements from the Brewer MK-III #150 scanning spectrophotometer during three campaigns. A total of 711 simultaneous spectra, measured under cloud-free conditions and covering a wide range of solar zenith angles (SZAs; from 14 to 70∘) and UV indexes (from 2.4 to 10.6), were used for the comparison. During the three measurement campaigns, the global UV spectral ratio BTS / Brewer was almost constant (at around 0.93) in the 305–360 nm region for SZAs below 70∘. Thus, the BTS calibration was stable during the whole period of study (∼ 1.5 years). Likewise, it showed no significant seasonal or SZA dependence in this wavelength region. Regarding the UV index, a good correlation between the BTS and the Brewer #150 was found, i.e., the dynamic range of the BTS is comparable to that of the Brewer #150. These results confirm the quality of the long-term performance of the BTS array spectroradiometer in measuring global UV irradiance.
Acceso Abierto
Evaluation of the uncertainty of the spectral UV irradiance measured by double- and single-monochromator Brewer spectrophotometers
(European Geosciences Union, 2025-10-30) González, Carmen; Vilaplana, Jose Manuel; Redondas, Alberto; López Solano, Javier; San Atanasio, José M.; Kift, Richard; Smedley, Andrew; Babal, Pavel; Díaz, Ana; Jepsen, Nis; Gacitúa, Guisella; Serrano, Antonio; Agencia Estatal de Investigación (España)
Brewer instruments are robust, widely used instruments that have been monitoring global solar ultraviolet (UV) irradiance since the 1990s, playing a key role in UV research. Unfortunately, the uncertainties of these measurements are rarely evaluated due to the difficulties involved in characterising the instruments. This evaluation is essential to determine the quality of the measurements as well as their comparability to other datasets. In this study, eight double- and two single-monochromator Brewers are characterised, and the uncertainty of their global UV measurements is estimated using the Monte Carlo method. This methodology is selected because it provides reliable uncertainty estimations and considers the nonlinearity of certain steps in the UV processing algorithm. The combined standard uncertainty depends on the Brewer instrument, varying between 2.5 % and 4 % between 310 and 350 nm. These uncertainties arise primarily from radiometric stability, cosine correction, and the uncertainty of the lamp used during calibration. At shorter wavelengths, the differences between single- and double-monochromator Brewers increase. For example, at 296 nm and a solar zenith angle (SZA) of 40°, the relative uncertainties of single Brewers range between 11 % and 23 %, whereas double Brewers have uncertainties of 3 %–5 %. As the measured wavelength decreases, the correction of stray light (for single Brewers), dark counts, and noise become the dominant sources of uncertainty. These results indicate that the accuracy of fully characterised double Brewers is sufficient for biological studies and trend detection, whereas single Brewers might be limited to wavelengths and SZAs below 305 nm and 70°, respectively.
Acceso Abierto
Monte Carlo Evaluation of Uncertainties of UV Spectra Measured With Brewer Spectroradiometers
(Advancing Earth and Space Sciences (AGU), 2023-12-26) González, Carmen; Vilaplana, Jose Manuel; Serrano, Antonio; Agencia Estatal de Investigación (AEI)
Precise spectral ultraviolet (UV) measurements are needed to ensure human protection as well as to support scientific research. Quantifying the uncertainty of the UV spectra recorded is crucial to evaluate the quality of the measurements which is needed, in turn, for the assessment of their reliability. However, for double-monochromator spectroradiometers, the analytical derivation of this uncertainty is a challenging task due to the difficulties involved in propagating individual uncertainties. Under these circumstances, a Monte Carlo simulation is a reliable alternative as it does not require the calculation of partial derivatives and considers both nonlinear effects and correlations in the data. In the present study, the uncertainty of the spectral UV irradiance measured by a Brewer MKIII spectrophotometer is evaluated using a Monte Carlo approach. This instrument belongs to the National Institute of Aerospace Technology and has successfully participated in several international campaigns, which ensures its precise calibration. The average expanded uncertainty (k = 2) of the global UV irradiance measured by this instrument varies between 10% at 300 nm and 7% at 363 nm. At shorter wavelengths, it increases sharply due to thermal and electronic noise as well as wavelength misalignment. The results indicate that a Brewer spectrophotometer is suitable for climatological studies and model validation. Nevertheless, a substantial reduction of these uncertainties might be required for accurately detecting long-term UV trends. Although the study focused on a Brewer spectrometer, the methodology used for the uncertainty analysis is general and can be adapted to most UV spectroradiometers.
Acceso Abierto
Validation of the GUM uncertainty framework and the Unscented transformation for Brewer UV irradiance measurements using the Monte Carlo method
(Elsevier, 2024-08-08) González, Carmen; Vilaplana, Jose Manuel; Parra Rojas, Francisco; Serrano, Antonio; Agencia Estatal de Investigación (AEI)
The uncertainty evaluation of spectral ultraviolet (UV) irradiance measurements is usually performed following the recommendations set by the GUM, the standard for uncertainty evaluation in metrology. In particular, the GUM uncertainty framework (GUF) is applied. Due to the difficulties in the propagation of uncertainties, it is standard practice to neglect the non-linearity of the irradiance model. To verify this assumption, the GUF is validated using the Monte Carlo method (MCM), as recommended by the GUM. As an alternative to these methods, an Unscented transformation (UT) has also been implemented and validated with the MCM. The data used are the UV scans recorded by a Brewer MKIII spectroradiometer at El Arenosillo Observatory. Evaluation of the spectral ratios between the combined standard uncertainties provided by the GUF, the UT, and the MCM showed that the agreement between the three methodologies is satisfactory.