Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Wiedner, Martina C.; Hills, R. E.; Carlstrom, J. E.; Lay, Oliver P.

doi:10.1086/320943

Cited by 41 publications

(42 citation statements)

References 18 publications

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“…Finally, phase correction using the 183 GHz water vapour line has been demonstrated at the James Clerk Maxwell Telescope -Caltech Submillimeter Observatory interferometer (Wiedner et al 2001). The ALMA radiometer system is to a large extent based on that concept.…”

Section: Radiometric Phase Correctionmentioning

confidence: 99%

Phase correction for ALMA with 183 GHz water vapour radiometers

Nikolic

Bolton

Graves

et al. 2013

A&A

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Fluctuating properties of the atmosphere, and in particular its water vapour content, give rise to phase fluctuations of astronomical signals which, if uncorrected, lead to rapid deterioration of performance of (sub)-mm interferometers on long baselines. The Atacama Large Millimetre/submillimeter Array (ALMA) uses a 183 GHz water vapour radiometer (WVR) system to help correct these fluctuations and provide much improved performance on long baselines and at high frequencies. Here we describe the design of the overall ALMA WVR system, the choice of design parameters and the data processing strategy. We also present results of initial tests that demonstrate both the large improvement in phase stability that can be achieved and the very low contribution to phase noise from the WVRs. Finally, we describe briefly the main limiting factors to the accuracy of phase correction seen in these initial tests; namely, the degrading influence of cloud and the residual phase fluctuations that are most likely to be due to variations in the density of the dry component of the air.

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Section: Radiometric Phase Correctionmentioning

confidence: 99%

Phase correction for ALMA with 183 GHz water vapour radiometers

Nikolic

Bolton

Graves

et al. 2013

A&A

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“…In this paper, we present the detailed characterization of phase fluctuation, improvement of phase fluctuation after the water vapor radiometer (WVR) phase correction method (Wiedner et al 2001;Nikolic et al 2013), coherence time calculation, and the cycle time analysis for the fast switching phase correction method using the data obtained in the ALMA long baseline campaigns. The results presented in this paper replace those reported previously by Matsushita et al (2012Matsushita et al ( , 2014Matsushita et al ( , 2016.…”

Section: Introductionmentioning

confidence: 99%

ALMA Long Baseline Campaigns: Phase Characteristics of Atmosphere at Long Baselines in the Millimeter and Submillimeter Wavelengths

Matsushita

Asaki

Fomalont

et al. 2017

PASP

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We present millimeter-and submillimeter-wave phase characteristics measured between 2012 and 2014 of Atacama Large Millimeter/submillimeter Array (ALMA) long baseline campaigns. This paper presents the first detailed investigation of the characteristics of phase fluctuation and phase correction methods obtained with baseline lengths up to ∼ 15 km. The basic phase fluctuation characteristics can be expressed with the spatial structure function (SSF). Most of the SSFs show that the phase fluctuation increases as a function of baseline length, with a power-law slope of ∼ 0.6. In many cases, we find that the slope becomes shallower (average of ∼ 0.2 − 0.3) at baseline lengths longer than ∼ 1 km, namely showing a turn-over in SSF. These power law slopes do not change with the amount of precipitable water vapor (PWV), but the fitted constants have a weak correlation with PWV, so that the phase fluctuation at a baseline length of 10 km also increases as a function of PWV. The phase correction method using water vapor radiometers (WVRs) works well, especially for the cases where PWV > 1 mm, which reduces the degree of phase fluctuations by a factor of two in many cases. However, phase fluctuations still remain after the WVR phase correction, suggesting the existence of other turbulent constituent that cause the phase fluctuation. This is supported by occasional SSFs that do not exhibit any turn-over; these are only seen when the PWV is low (i.e., when the WVR phase correction works less effectively) or after WVR phase correction. This means that the phase fluctuation caused by this turbulent constituent is inherently smaller than that caused by water vapor. Since in these rare cases there is no turn-over in the SSF up to the maximum baseline length of ∼ 15 km, this turbulent constituent must have scale height of 10 km or more, and thus cannot be water vapor, whose scale height is around 1 km. Based on the characteristics, this large scale height turbulent constituent is likely to be water ice or a dry component. Excess path length fluctuation after the WVR phase correction at a baseline length of 10 km is large ( 200 µm), which is significant for high frequency (> 450 GHz or < 700 µm) observations. These results suggest the need for an additional phase correction method to reduce the degree of phase fluctuation, such as fast switching, in addition to the WVR phase correction. We simulated the fast switching phase correction method using observations of single quasars, and the result suggests that it works well, with shorter cycle times linearly improving the coherence.

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“…units is primarily due to fluctuations in atmospheric water vapour along the line-ofsight of each antenna. Theory predicts a relationship between phase delay induced in radio signals and the line-of-sight atmospheric water vapour content, expressed as [15,16]:…”

Section: Resultsmentioning

confidence: 99%

IRMA as a Potential Phase Correction Instrument: Results from the SMA Test Campaign

Naylor

Phillips

Francesco

et al. 2008

Int J Infrared Milli Waves

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The Infrared Radiometer for Millimetre Astronomy (IRMA) is a realtime water vapour monitor, whose sensitivity and temporal response make it a candidate instrument for the correction of phase distortion caused by atmospheric water vapour in millimetre wavelength interferometers. We present results from a test campaign in which two IRMA devices were mounted on two antennae of the Smithsonian Submillimeter Array (SMA) located atop Mauna Kea, Hawaii. The IRMA measurements are compared to each other, and to phase information derived from astronomical interferometric data to assess their utility as a potential tool in phase correction.

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Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Cited by 41 publications

References 18 publications

Phase correction for ALMA with 183 GHz water vapour radiometers

Phase correction for ALMA with 183 GHz water vapour radiometers

ALMA Long Baseline Campaigns: Phase Characteristics of Atmosphere at Long Baselines in the Millimeter and Submillimeter Wavelengths

IRMA as a Potential Phase Correction Instrument: Results from the SMA Test Campaign

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