Overview of Atmospheric Simulation Efforts in CTA

Vrastil, M.

doi:10.1051/epjconf/201714401014

Cited by 6 publications

(6 citation statements)

References 9 publications

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“…standard deviation divided by its mean, for each seasonal periods. That relative deviation lies always below 2%, hence fulfilling the CTA requirements [10]. Moreover, we clearly see that there is a significant difference with respect to the PROD3 simulation profile, reaching up to 12% on average for one altitude bin (see Figure 3) at the northern CTA site.…”

Section: Density Over Altitudesupporting

confidence: 65%

Studying molecular profiles above the Cherenkov Telescope Array sites

Munar-Adrover

Gaug

2019

EPJ Web Conf.

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The Cherenkov Telescope Array (CTA) will bring a whole new insight to the gamma-ray Universe. In order to fulfill its performance requirements, we need to understand and correct the atmospheric effects that influence the acquired instrument data. One such systematic effect is due to the varying molecular density profile with time. We have studied such profiles for both CTA sites using publicly available historical data assimilation archives. Our study reveals that we can distinguish at least three differentiated seasonal periods at the northern site and at least two at the southern site, that allow to model the molecular part of the atmosphere using average profiles, as done with current Cherenkov telescope projects. Seasonal transitions are smoother at the southern site than at the northern one. Moreover, the latter shows a greater amplitude in density variations at an altitude of 15 km. We also explored deviations of the molecular profiles with respect to their mean values using a 5-years data set and concluded that they are always found within specifications.

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Section: Density Over Altitudesupporting

confidence: 65%

Studying molecular profiles above the Cherenkov Telescope Array sites

Munar-Adrover

Gaug

2019

EPJ Web Conf.

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“…The assumed error of only 2-3% rms induced by this choice resulted to never limit their overall systematic uncertainty, by a factor of several times higher [5,6]. Whether such a statement is still true for the CTA, is currently being investigated [37,38]. The difference is not only due to the stricter requirements on the CTA's accuracy, but also to its wider coverage of gamma-ray energies.…”

Section: The Molecular Profilementioning

confidence: 99%

“…The CTA will carry out a radio sonde campaign at its Southern site and rely on a database covering several years of MAGIC LIDAR [12] data to assess the latter. A dedicated simulation effort is now ongoing in CTA [38] to directly assess the effect of typical and maximum variations of the density profile using the vast historical database of the GDAS 3 , together with assumptions on the accuracy of these. The outcome of these simulations should be ready for the next AtmoHEAD conference and answer the question of how many different molecular profiles will be required for the CTA data analysis.…”

Section: The Molecular Profilementioning

confidence: 99%

CTA Atmospheric Calibration

Gaug

2017

EPJ Web Conf.

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Abstract. The main contribution to the systematic uncertainties of Atmospheric Imaging Cherenkov Telescopes (IACTs) currently stems from the uncertainty in the determination of atmospheric properties for a given moment of observation. This technique uses the atmosphere as a calorimeter of gamma-ray induced atmospheric air showers and measures the amount of Cherenkov light collected by large mirrors and focused towards a pixellized camera. Atmospheric conditions affect the measured Cherenkov light yield in several ways: the air-shower development itself, the variation of the Cherenkov angle with altitude and the loss of photons due to scattering and absorption of Cherenkov light. Although IACTs use to be located at astronomical sites, characterized by extremely clear atmospheric conditions, the local atmosphere should be continuously monitored, in terms of molecular density profiles, aerosol extinction profiles, and clouds. Moreover, a general understanding of the site and particularly aerosol climatology is desirable for a robust interpretation of the sensing instruments' data. Here, the strategy of the Cherenkov Telescope Array (CTA) on atmospheric monitoring is presented, designed to ensure that the related systematic uncertainties are brought down by at least a factor of two with respect to current installations. Additionally, a more intelligent scheduling scheme is aimed at, where source observations are selected using dedicated auxiliary atmospheric monitoring instruments and taking into account the feasibility of a later analysis according to the underlying scientific case. This plan should reduce data loss during offline data selection and enhance the effective duty cycle of the CTA.

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“…From these average scenarios, and the extremes also seen in Fig. 2, the input models for detailed simulations have been created [24].…”

Section: Molecular Density Profilesmentioning

confidence: 99%