Sunbelt Spectra comparison with Standard ASTM G173: the Chilean case
Two spectra of solar direct normal irradiance (including circumsolar) are estimated based on spatio-temporal averages of the relevant atmospheric parameters extracted from two different databases: MODIS satellite sensor retrievals and AERONET sun photometer network. The satellite database is used to calculate an average spectrum for the area of the Atacama Desert. The AERONET database is used for two purposes: (i) to apply bias-removal linear methods to correct the MODIS parameters over Atacama, and (ii) to calculate an average local spectrum for the Paranal station. The SMARTS radiative transfer model is used to obtain the three spectra developed in this study. Both the Atacama and Paranal spectra are compared against each other and also to the world reference, ASTM G173. In one of the cases, significant differences are found for short wavelengths. In order to quantify the relative importance of these spectral differences, the propagation of errors due to the use of each spectrum is evaluated for CSP applications over the Atacama Desert, considering twelve different scenarios involving the reflectance, transmittance or absorptance of various materials.
Citation: Marzo, Aitor & Polo, Jesus & Wilbert, Stefan & Gueymard, Chris & Jessen, Wilko & Ferrada, Pablo & Alonso-Montesinos, Joaquín & Ballestrín, Jesús. (2017). Sunbelt Spectra comparison with Standard ASTM G173: the Chilean case. AIP Conference Proceedings. 2033. 10.1063/1.5067195.
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A 10-year characterization of the Saharan Air Layer lidar ratio in the subtropical North Atlantic
May 10, 2019
Particle extinction-to-backscatter ratio (lidar ratio) is a key parameter for a correct interpretation of elastic lidar measurements. Of particular importance is the determination of the lidar ratio of the Saharan Air Layer mineral dust transported into the free troposphere over the North Atlantic region. The location of the two sun photometer stations managed by the Izaña Atmospheric Research Centre (IARC) on the island of Tenerife and a decade of available micropulse lidar (MPL) data allow us to determine the lidar ratio under almost pure-dust conditions. This result can be considered representative of the Saharan dust transported westward over the North Atlantic in the subtropical belt.
Three different methods have been used to calculate the lidar ratio in this work: (1) using the inversion of sky radiance measurements from a sun–sky photometer installed at the Izaña Observatory (2373 m a.s.l.) under free-troposphere conditions; (2) the one-layer method, a joint determination using a micropulse lidar sited at the Santa Cruz de Tenerife sea-level station and photometric information considering one layer of aerosol characterized by a single lidar ratio; and (3) the two-layer method, a joint determination using the micropulse lidar and photometric information considering two layers of aerosol with two different lidar ratios. The one-layer method only uses data from a co-located photometer at Santa Cruz de Tenerife, while the two-layer conceptual approach incorporates photometric information at two heights from the observatories of Izaña and Santa Cruz de Tenerife. The almost pure-dust lidar ratio retrieval from the sun–sky photometer and from the two-layer method give similar results, with lidar ratios at 523 nm of 49 ± 6 and 50 ± 11 sr. These values obtained from a decade of data records are coincident with other studies in the literature reporting campaigns in the subtropical North Atlantic region. This result shows that the two-layer method is an improved conceptual approach compared to the single-layer approach, which matches the real lower-troposphere structure well. The two-layer method is able to retrieve reliable lidar ratios and therefore aerosol extinction profiles despite the inherent limitations of the elastic lidar technique.
We found a lack of correlation between lidar ratio and Ångström exponent (α), which indicates that the dust lidar ratio can be considered independent of dust size distribution in this region. This finding suggests that dust is, under most atmospheric conditions, the predominant aerosol in the North Atlantic free troposphere, which is in agreement with previous studies conducted at the Izaña Observatory.
Citation: Berjón, A., Barreto, A., Hernández, Y., Yela, M., Toledano, C., and Cuevas, E.: A 10-year characterization of the Saharan Air Layer lidar ratio in the subtropical North Atlantic, Atmos. Chem. Phys., 19, 6331-6349, https://doi.org/10.5194/acp-19-6331-2019, 2019.
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Aerosol measurements with shipborne sun-sky-lunar photometer and collocated multiwavelength Raman polarization lidar over the Atlantic Ocean
A shipborne sun-sky-lunar photometer was tested in two trans-Atlantic cruises aboard the German research vessel Polarstern from 54° N to 54° S. A full diurnal cycle of mixed dust-smoke episode measured with shipborne CE318-T is presented for the first time. Latitudinal distribution of AOD from the shipborne CE318-T, Raman lidar and MICROTOPS II shows the same trend with high values at 0 ~ 20° N dust transported belt and low values at Southern Hemisphere. Coefficient of determination for the linear regression between MICROTOPS II and shipborne sun-sky-lunar photometer was 0.993 for AOD at 500 nm and 0.896 for Ångström exponent at 440–870 nm.
Citation: Yin, Zhenping & Ansmann, Albert & Baars, Holger & Martin, Radenz & Jimenez, Cristofer & Engelmann, Ronny & Seifert, Patric & Herzog, Alina & Ohneiser, Kevin & Hanbuch, Karsten & Blarel, L & Goloub, Philippe & Dubois, Gael & Victori, Stephane & Maupin, Fabrice. (2019). Aerosol measurements with shipborne sun-sky-lunar photometer and collocated multiwavelength Raman polarization lidar over the Atlantic Ocean. Atmospheric Measurement Techniques Discussions. 1-21. 10.5194/amt-2019-132.
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