Radiometric monitoring of atmospheric water vapor
as it pertains to phase correction in millimeter interferometry

Sutton, E. C.; Hueckstaedt, R. M.

doi:10.1051/aas:1996268

Cited by 11 publications

(16 citation statements)

References 12 publications

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“…There is an extensive literature on phase correction at radio wavelengths ; an incomplete list of articles includes Westwater (1967) ;Schaper, Staelin, & Waters (1970) ; Holdaway (1992) ; Sutton & Hueckstaedt (1996) ;Lay (1997aLay ( , 1997b. Basically there are two di †erent methods.…”

Section: Phase Correction Methodsmentioning

confidence: 99%

“…An increase in the amount of PWV by 0.16 mm is approximately equivalent to lengthening the electromagnetic waveÏs electrical path by an additional 1 mm (Sutton & Hueckstaedt 1996). The sensitivity, plotted in the bottom panel of Figure 2, indicates by how many kelvins the sky emission will change per millimeter of additional electrical path.…”

Section: Atmospheric Emission On Mauna Keamentioning

confidence: 99%

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Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Wiedner¹,

Hills²,

Carlstrom³

et al. 2001

ApJ

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The angular resolution that can be obtained by ground-based aperture synthesis telescopes at millimeter and submillimeter wavelengths is limited by phase Ñuctuations caused by water vapor in the EarthÏs atmosphere. We describe here the successful correction of such Ñuctuations during observations at 0.85 mm wavelength with an interferometer consisting of the James Clark Maxwell Telescope and the Caltech Submillimeter Observatory. This was achieved by using two 183 GHz heterodyne radiometers to measure the water vapor content along the line of sight of each telescope. Further development of such techniques will enable future telescopes, such as the Submillimeter Array and the Atacama Large Millimeter Array, to reach their full capability, providing a resolution of up to 0A .01.

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Section: Phase Correction Methodsmentioning

confidence: 99%

Section: Atmospheric Emission On Mauna Keamentioning

confidence: 99%

Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Wiedner¹,

Hills²,

Carlstrom³

et al. 2001

ApJ

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“…A final uncertainty involved in making absolute radiometric phase corrections is errors in the theoretical atmospheric models relating w and T• [Elgered, 1993]. Sutton and Hueckstaedt [1997] point out that model errors are by far the dominant uncertainties when considering absolute radiometric phase correction, and they have calculated a number of models with different line shapes and different empirically determined water vapor continuum "fudge factors." Row 18 in Table 1 lists the approximate differences between the various rnodels at various frequencies.…”

Section: Absolute Radiometric Phase Correctionsmentioning

confidence: 99%

“…The solutions would then be extrap-CARILLI AND HOLDAWAY: TROPOSPHERIC PHASE CALIBRATION olated to the observing frequency of the main array using the linear relationship between tropospheric phase and frequency (equation (1)). This would require a separate correlator and IF system, and complications may arise because the wet troposphere becomes dispersive at frequencies higher than about 400 GHz [Sutton and Hueckstaedt, 1997]. For PA and FS calibration, if the bulk of the phase fluctuations occur in a thin turbulent layer, it may be possible to perform an intelligent method of data interpolation, such as forward projection using a physical model for the troposphere and Kalman filtering of the spatial time series, to account for the motion of the atmosphere across the array.…”

Section: Correctionmentioning

confidence: 99%

Tropospheric phase calibration in millimeter interferometry

Carilli¹,

Holdaway²

1999

Radio Science

109

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Abstract. We review millimeter interferometric phase variations caused by variations in the precipitable water vapor content of the troposphere, and we discuss techniques proposed to correct for these variations. We present observations with the Very Large Array (VLA) at 22 and 43 GHz designed to test these techniques. We find that both the fast switching and paired array calibration techniques are effective at reducing tropospheric phase noise for radio interferometers. In both cases, the residual rms phase fluctuations after correction are independent of baseline length for b > b eff-These techniques allow for diffraction-limited imaging of faint sources on arbitrarily long baselines at millimeter wavelengths. We consider the technique of tropospheric phase correction using a measurement of the precipitable water vapor content of the troposphere via a radiometric measurement of the brightness temperature of the atmosphere. Required sensitivities range from 20 mK at 90 GHz to 1 K at 185 GHz for the millimeter array (MMA) and to 120 mK for the VLA at 22 GHz. The minimum gain stability requirement is 200 at 185 GHz at the MMA, assuming that the astronomical receivers are used for radiometry. This increases to 2000 for an uncooled system. The stability requirement is 450 for the cooled system at the VLA at 22 GHz. To perform absolute radiometric phase corrections also requires knowledge of the tropospheric parameters and models to an accuracy of a few percent. It may be possible to perform an "empirically calibrated" radiometric phase correction, in which the relationship between fluctuations in brightness temperature differences and fluctuations in interferometric phases is calibrated by observing a strong celestial calibrator at regular intervals. A number of questions remain concerning this technique, including the following: (1) Over what timescale and distance will this technique allow for radiometric phase corrections when switching between the source and the calibrator? (2) How often will calibration of the r• ms -qbrm s relationship be required?

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“…The algorithms for obtaining a path correction from an emission measure are not considered here (see e.g. Sutton & Hueckstaedt 1996), although the accuracy needed is addressed.…”

Section: Introductionmentioning

confidence: 99%

Phase calibration and water vapor radiometry for millimeter-wave arrays

Lay

1997

Astron. Astrophys. Suppl. Ser.

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Abstract. Correcting for the fluctuations in atmospheric path length caused by water vapor is a major challenge facing millimeter-and submillimeter-wave interferometers, and one that must be overcome to obtain routine sub-arcsecond resolution. Using the model for the power spectrum of phase fluctuations developed in Lay (1997), the existing technique of phase referencing to a bright calibrator object is analysed. It is shown that the phase errors after calibration have comparable contributions from both the target and calibrator measurements.The technique of water vapor radiometry, where the amount of emission from water vapor in the beam of each antenna is used to estimate a path correction, is also examined. It is found that there are two levels on which a correction can be made. The simplest corrects just the fluctuations within each on-source period; the calibration requirements for the radiometers are modest, and this partial correction can give a substantial improvement in the resolution and coherence time of an interferometer. The atmospheric fluctuations on longer timescales remain uncorrected, however, and are significant. To remove these, a full correction is required, which measures the change in the path difference that occurs when moving between the calibrator and the target, in addition to the on-source fluctuations. Since there can be a large difference in airmass between the calibrator and the target, measuring this change requires that the radiometers have the same response to a given column of water vapor to within ∼ 0.1%. Two possible methods of achieving this very stringent limit are outlined.For reasonable observing conditions at 230 GHz, it is predicted that the effective atmospheric "seeing" (the apparent smearing of the sky brightness distribution due to the atmosphere) is improved from 0.6 (phase referencing every 25 minutes) to 0.3 (phase referencing and partial radiometric correction). A full radiometric correction would, in principle, restore perfect seeing.

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Radiometric monitoring of atmospheric water vapor as it pertains to phase correction in millimeter interferometry

Cited by 11 publications

References 12 publications

Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Interferometric Phase Correction Using 183 GHzGHz Water Vapor Monitors

Tropospheric phase calibration in millimeter interferometry

Phase calibration and water vapor radiometry for millimeter-wave arrays

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