Water Vapor Retrievals from Spectral Direct Irradiance Measured with an EKO MS-711 Spectroradiometer—Intercomparison with Other Techniques

Abstract

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.

Spectral Aerosol Radiative Forcing and Efficiency of the La Palma Volcanic Plume over the Izaña Observatory

“…EKO performs one spectrum per minute, with an exposure time ranging from 10 ms to 5 s depending on the intensity of the irradiance and sky conditions and a field of view of 5 • . The EKO has been comprehensively tested in the IZO WMO-CIMO testbed activities (more details in García et al [33] and García et al [34]).…”

Comparison of Cimel Sun-Photometer and Ground-Based Gnss Integrated Water Vapor Over South-Western European Sites

“…The retrieval method is described in the following lines. A more detailed description can be found in García et al (2021). The response of the instrument can be modeled by the following expression:…”

Characterisation and Field Test of a Simple AvaSpec Array Spectroradiometer for Solar Irradiance Measurements at an Alpine Site

“…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].…”