ACA phase calibration scheme with the ALMA water vapor radiometers

Yoshiharu Asaki; Satoki Matsushita; Koh-Ichiro Morita; Bojan Nikolic

doi:10.1117/12.925986

17 September 2012 ACA phase calibration scheme with the ALMA water vapor radiometers

Yoshiharu Asaki, Satoki Matsushita, Koh-Ichiro Morita, Bojan Nikolic

Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 84443K (2012) https://doi.org/10.1117/12.925986
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

In Atacama Large Millimeter/submillimeter Array (ALMA) commissioning and science verification we have conducted a series of experiments of a novel phase calibration scheme for Atacama Compact Array (ACA). In this scheme water vapor radiometers (WVRs) devoted to measurements of tropospheric water vapor content are attached to ACA’s four total-power array (TP Array) antennas surrounding the 7 m dish interferometer array (7 m Array). The excess path length (EPL) due to the water vapor variations aloft is fitted to a simple two-dimensional slope using WVR measurements. Interferometric phase fluctuations for each baseline of the 7 m Array are obtained from differences of EPL inferred from the two-dimensional slope and subtracted from the interferometric phases. In the experiments we used nine ALMA 12-m antennas. Eight of them were closely located in a 70-m square region, forming a compact array like ACA. We supposed the most four outsiders to be the TP Array while the inner 4 antennas were supposed to be the 7 m Array, so that this phase correction scheme (planar-fit) was tested and compared with the WVR phase correction. We estimated residual root-mean-square (RMS) phases for 17- to 41-m baselines after the planar-fit phase correction, and found that this scheme reduces the RMS phase to a 70 – 90 % level. The planar-fit phase correction was proved to be promising for ACA, and how high or low PWV this scheme effectively works in ACA is an important item to be clarified.

Citation Download Citation

Yoshiharu Asaki, Satoki Matsushita, Koh-Ichiro Morita, and Bojan Nikolic "ACA phase calibration scheme with the ALMA water vapor radiometers", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 84443K (17 September 2012); https://doi.org/10.1117/12.925986

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