Ciências e Aplicações Geoespaciais - Dissertações - CRAAM

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Navegando Ciências e Aplicações Geoespaciais - Dissertações - CRAAM por Autor "Espinoza, Deysi Veronica Cornejo"

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    Dissertação
    Determinação da opacidade atmosférica em comprimentos de ondas submilimétricas
    Espinoza, Deysi Veronica Cornejo (2017-07-28)

    Escola de Engenharia Mackenzie (EE)

    To understand the nature of the solar explosive radiation mechanisms at high frequency radio waves, which depends on the interpretation of the flux density spectrum (S), it is necessary to have a good estimate of the accuracy of S . For this reason, the atmospheric opacity determination is essential, to correct the observed solar radiation flux from radio telescopes in the ground. For high frequencies (e.g. in the sub-millimeter and infrared wavelength), the water vapor is mainly responsible of the atmospheric opacity. Thus, the solar radiation collected by the radio telescope can be strongly attenuated up to a factor of 1000 (e.g. at 405 GHz). Therefore, it is necessary to have a reliable estimate of the atmospheric opacity. The main aim of this work is to determine the atmospheric opacity at 212 and 405 GHz using the solar brightness method. Comparing with the characteristics of other methods in the literature, we find that this one allows to determine the atmospheric opacity up to considerably high values, and only depends on one parameter. Namely, the product 𝑃 = 𝜂𝑇, where 𝑇 is the brightness temperature of the Sun measured at 212 and 405 GHz and 𝜂 is the beam efficiency; we assume that the 𝑃 value is constant even though 𝑇 and 𝜂 are not well known individually. For the development of the present work, we were used approximately 18 thousand solar scans recorded by the Submillimetric Solar Telescope (SST, CASLEO, 2552 m altitude), for the period between 2002 and 2015, where only clear days with low opacity were considered. Using the solar brightness method, the 𝑃 value was calculated at 212 and 405 GHz. For the four beam at 212 GHz, we obtained: ¯ 𝑃 = 2446 ± 149 K (beam 1); ¯ 𝑃 = 2489±184 K (beam 2); ¯ 𝑃 = 2541±223 K (beam 3); ¯ 𝑃 = 2361±199 K (beam 4) and for the two beams at 405 GHz we obtained: ¯ 𝑃 = 3241±331 K (beam 5) and ¯ 𝑃 = 3299 ± 276 K (beam 6). Using the mean values ¯ 𝑃, the atmospheric opacities 𝜏212 and 𝜏405 were determined at 212 and 405 GHz, respectively. The correlation between the opacities 𝜏212 and 𝜏405, show that the opacity at 405 GHz ∼ 7 times more than that at 212 GHz. In addition, we also find that the atmospheric opacities determined with the method proposed in this work show an excellent correlation with the water vapor content, when this is measured simultaneously.