# Erythermal Solar Irradiance, UVER, and UV Index from Ground-Based Data in Central Spain
## 2 Materials and Methods
### Equipment  
A YES UVB-1 pyroanometer (Yankee Environmental Systems Inc., Turners Falls, Massachusetts, 01376) on a horizontal surface [4], which has a spectral sensitivity close to the erytal action spectrum, was used to record UV-B irradiance [4]. The YES UVB-1 sensor spectral response ranges between 280 and 320 nm, and is similar to the erytal (sunburn) and DNA damage action spectra. The YES UV-1 Pyroanometer characteristics for solar zenith angle between 0-60\({}^{\circ}\) has a cosine response above +5%, and the sensitivity is 1.9 Wm\({}^{-2}\)V\({}^{-1}\). The YES UVB-1 sensor was calibrated by the Spanish National Institute in Aerospace Technology (INTA). The radiometer spectral response measured indoors was compared with a Brewer MKIII spectroradiometer outdoors [26]. Sensor uncertainty ranged between 8-9% [27]. From the calibration results, a double input matrix was obtained whose terms depend on the zenith angle and total ozone column, (TOC), values. Erythermal effective irradiance was thus obtained from the sensor output-voltage, multiplying the sensor voltage signal by the corresponding term of the calibration matrix [28]. The corresponding UVER values in Wm\({}^{-2}\) were subsequently obtained. Taking into account [PERSON] and [PERSON] [29] results, experimental evaluation uncertainties ranged between 4.6-7%.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Period** & **Latitude** & **Longitude** & **Altitude** & **One Minute Data** & **Hourly** & **Daily** & **Month** \\  & (\({}^{\circ}\)N) & (\({}^{\circ}\)W) & (m.a.s.l.) & **One Minute Data** & **Data** & **Data** & **Data** \\ \hline
2013–2019 & 41.7 & 4.7 & 702 & 1,347,429 & 24,132 & 1881 & 66 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Geographical coordinates and database figures for the station.  
From satellite-based remote sensing, daily total ozone column data, TOC, were obtained, from TOMS/OMI, (Total Ozone Mapping Spectrometer (NASA)/ Ozone Monitoring Instrument), onboard the Earth-Probe/Aura satellites. Data are the average of a square with a 0.2\({}^{\circ}\) side centered on the coordinates of the measurement station. Daily TOC values were retrieved from ([[http://disc.sci.gsfc.nasa.gov/Aura/data-holdings/OMI/omt03_v003.shtml](http://disc.sci.gsfc.nasa.gov/Aura/data-holdings/OMI/omt03_v003.shtml)]([http://disc.sci.gsfc.nasa.gov/Aura/data-holdings/OMI/omt03_v003.shtml](http://disc.sci.gsfc.nasa.gov/Aura/data-holdings/OMI/omt03_v003.shtml))) at the Valladolid station [30,31]. Daily TOC values range from 282 to 365 DU (Dodson units). In general, daily TOC values display a yearly evolution at the measurement station with maximum values in spring (April, May) and minimum values in autumn (October, November).  
A CR23X Campbell data logger was connected to the YES UVB-1 solar sensor. The adapted software-enabled UVB solar irradiance to be recorded each 10 s. Average values were evaluated every one minute and from them hourly and daily values were obtained [4].  
Following previous studies and publications [23], a useful data quality control test established the measured data series before processing. The test used aimed to remove faulty data and inaccurate measurements resulting from the response error of the sensor. The test assumes that data are homogeneous, and that data variation is only due to meteorological and climatic situations and that there are no other error reasons. The sensor detection limits and subsequent conditions that made up the quality control test were given by the following expression: UVB \(\leq\) 1.2 UVB\({}_{0}\), where UVB is the measured value and UVB\({}_{0}\) is the horizontal extraterrestrial solar UVB irradiation. After the test, a total of 5267 values were rejected due to erroneous data (anomalous recording of the sensors). The final number of data that passed the quality test is shown in Table 1.