Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

Radford, Simon J. E.; Peterson, Jeffrey B.

doi:10.1088/1538-3873/128/965/075001

Cited by 31 publications

(38 citation statements)

References 48 publications

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“…For Cerro Chajnantor summit, the PWV ratio with the plateau is 0.68, which indicates 32% less PWV compared to the plateau and for our long‐term study. Although this value is close to previous results [i.e., Bustos et al , ; Radford and Peterson , ], our study is longer term and therefore averages out temporal variabilities in the atmospheric quantities.…”

Section: Discussionsupporting

confidence: 91%

“…The scale heights reported in this paper, Table , are within the suggested values shown in Radford and Peterson [].…”

Section: Comparison and Correlations In Pwvsupporting

confidence: 87%

“…An atmospheric measurement campaign was performed by Turner and Mlawer [2010] on Cerro Toco in 2009. The atmospheric transparency has been intensively studied by Radford and Chamberlin [2000], Giovanelli et al [2001], Radford [2011], andRadford andPeterson [2016]. In addition, the differences in PWV between the Chajnantor Plateau and Cerro Chajnantor were shown in Bustos et al [2014] for a time span of 5 days.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the distribution of precipitable water vapor in the Chajnantor area

2016

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Key Points.• We validate a method to convert from sub-mm opacity to PWV.• Tipper data was successfully calibrated and correlate to high degree with data from independent sources.• Found a PWV ratio between Cerro Chajnantor and Chajnantor Plateau of 0.68.In this work, we present results from a long-term precipitable water vapor (PWV) study in the Chajnantor area, in northern Chile. Data from several instruments located at relevant sites for sub-millimeter and mid-infrared astronomy were processed to obtain relations between the atmospheric conditions among the sites. The data used for this study can be considered the richest dataset to date, because of the geographical sampling of the region, including sites at different altitudes, a time span from 2005 to 2014, and the different techniques and instruments used for the measurements. We validate a method to convert atmospheric opacity from 350 µm tipper radiometers to PWV. An average of 0.68 PWV ratio between Cerro Chajnantor and Llano of Chajnantor was found.

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Section: Discussionsupporting

confidence: 91%

“…The scale heights reported in this paper, Table , are within the suggested values shown in Radford and Peterson [].…”

Section: Comparison and Correlations In Pwvsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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Analysis of the distribution of precipitable water vapor in the Chajnantor area

2016

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“…Conditions on Dome C, Antarctica (3260-m elevation), are significantly better than at the South Pole (Calisse et al 2004), and Ridge A on the Antarctic high plateau (4050-m elevation) may have the lowest water vapor on the planet (Sims et al 2012). Adapted from Radford and Peterson (2016).…”

Section: Opacity Measurementsmentioning

confidence: 99%

Propagation Effects: Neutral Medium

Thompson

Moran

Swenson

2017

Astronomy and Astrophysics Library

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The neutral gas in the atmosphere has a significant effect on signals passing through it. We are concerned with three types of effects. First, the large-scale structures in the media give rise to refractive effects. These effects, which can be analyzed in terms of geometrical optics and Fermat's principle, are the deflection of the radio waves and the change of the propagation velocity. Second, radiation can be absorbed. Finally, radiation can be scattered by the turbulent structure of the media. The phenomenon of scattering results in scintillation, or seeing.In the troposphere, water vapor plays a particularly important role in radio propagation. The refractivity of water vapor is about 20 times greater in the radio range than in the near-infrared or optical regimes. The phase fluctuations in radio interferometers at centimeter, millimeter, and submillimeter wavelengths are caused predominantly by fluctuations in the distribution of water vapor. Water vapor is poorly mixed in the troposphere, and the total column density of water vapor cannot be accurately sensed from surface meteorological measurements. Uncertainties in the water vapor content are a serious limitation to the accuracy of VLBI measurements. Small-scale (< 1 km) fluctuations in water vapor distribution limit the angular resolution of connected-element interferometers in the absence of wavefront correction techniques. Furthermore, spectral lines of water vapor cause substantial absorption at frequencies above 100 GHz and usually render the troposphere highly opaque at frequencies between 1 and 10 THz (300 and 30 m). Thus, any discussion of the neutral atmosphere must be primarily concerned with the effects of water vapor. Propagation in the neutral atmosphere from the point of view of radio communications is discussed by Crane (1981) and Bohlander et al. (1985).Our interest in the propagation media arises because the media degrade interferometric measurements of radio sources. Alternately, observations of radio sources can be used to probe the characteristics of the propagation media. Radio interferometric measurements have been used widely for this purpose.

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“…Astronomical observations in the millimeter and sub-millimeter wavelength range require that atmospheric effects affecting absorption at these wavelengths are kept to a minimum (Chamberlin & Grossman 2012, Radford & Peterson 2016, Cortés et al 2016. The main factor contributing to the atmospheric opacity is water vapor, which very efficiently absorbs light in the THz range , Kuhn et al 2002 due to a continuum absorption spectrum formed by collisionally broadened absorption lines of water vapor in this frequency range (Clough et al 1989, Pickett et al 1998, Turner et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

Molano¹,

Suárez²,

Restrepo

et al. 2017

PASP

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Abstract. We set out to evaluate the potential of the Colombian Andes for millimeter-wave astronomical observations. Previous studies for astronomical site testing in this region have suggested that nighttime humidity and cloud cover conditions make most sites unsuitable for professional visible-light observations. Millimeter observations can be done during the day, but require that the precipitable water vapor column above a site stays below ∼10 mm. Due to a lack of direct radiometric or radiosonde measurements, we present a method for correlating climate data from weather stations to sites with a low precipitable water vapor column. We use unsupervised learning techniques to low-dimensionally embed climate data (precipitation, rain days, relative humidity, and sunshine duration) in order to group together stations with similar long-term climate behavior. The data were taken over a period of 30 years by 2046 weather stations across the Colombian territory. We find 6 regions with unusually dry, clear-sky conditions, ranging in elevations from 2200 to arXiv:1705.06121v4 [astro-ph.IM] 15 Sep 2017Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing 2 3800 masl. We evaluate the suitability of each region using a quality index derived from a Bayesian probabilistic analysis of the station type and elevation distributions. Two of these regions show a high probability of having an exceptionally low precipitable water vapor column. We compared our results with global precipitable water vapor maps and find a plausible geographical correlation with regions with low water vapor columns (∼ 10 mm) at an accuracy of ∼ 20 km. Our methods can be applied to similar datasets taken in other countries as a first step toward astronomical site evaluation.

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Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

Cited by 31 publications

References 48 publications

Analysis of the distribution of precipitable water vapor in the Chajnantor area

Analysis of the distribution of precipitable water vapor in the Chajnantor area

Propagation Effects: Neutral Medium

Low Dimensional Embedding of Climate Data for Radio Astronomical Site Testing in the Colombian Andes

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