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The atmospheric attenuation in the THz to mid-IR band

Grant number: 19/22205-0
Support type:Scholarships in Brazil - Post-Doctorate
Effective date (Start): December 01, 2019
Effective date (End): November 30, 2020
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Astronomical Instrumentation
Principal researcher:Carlos Guillermo Giménez de Castro
Grantee:Jorge Fernando Valle Silva
Home Institution: Escola de Engenharia (EE). Universidade Presbiteriana Mackenzie (UPM). Instituto Presbiteriano Mackenzie. São Paulo , SP, Brazil
Associated research grant:13/24155-3 - Solar flare diagnostic in an unprecedented frequency range from microwaves to THz frequencies: challenges for interpretation (flat), AP.TEM


Atmospheric opacity plays a key role in Astronomical observations since it affects the absolute flux measurement determination. Assuming a plane-parallel and homogeneous atmosphere an astronomical signal will be attenuated by a factor Ľ sec ¶, (1) where Ľ is the optical depth at frequency ½ in the Zenith direction and ¶ is the zenith distance of the observing direction. Dependency of the attenuation with wavelength is qualitatively represented in Figure 1. It is well known that the atmospheric attenuation at visible wavelengths is very weak as well as for radio meter to decimeter wavelengths. However millimeter observations start to be attenuated, for this reason telescopes operating at frequencies above 100 GHz are located above ground level to reduce the atmospheric mass over the observatory, the higher the frequency the higher the observa- tory height. However, observations above 1 THz (» = 0.3 mm) are extremely attenuated even when observing at 5, 000 meter above sea level with Ä d 1 only for a few days every year. At a frequency around 15 THz (» = 0.02 mm) the atmospheric opacity significantly drops allowing observations at mid-altitude.There are however, few works describing the THz to mid-IR range atmospheric opacity in de- tail. Pardo et al. (2001) developed a new model that computes the electromagnetic wave propagation through the atmosphere from 1 GHz to 2 THz. The authors wrote a computer program called ATM that is freely distributed and widely used in different observatories. Paine (2018) also developed an atmospheric model and produced a computer program called am which is widely used to compute the atmospheric transmission from 1 GHz to 1 THz. More recently Eriksson, P. and Buehler, S.A. and Davis, C.P. and Emde, C. and Lemke, O. (2011) have developed an atmospheric model that computes the radiative transfer between 3 mm (½ = 100 GHz) and 0.001 mm (½ = 300 THz). The Atmospheric Radiative Transfer Simulator (arts) is a public domain open source software written in C++ which in the present version 2 can handle scattering and spherical geometries. (AU)

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