ALMA Memo 491 Does the ACA Need Phase Compensation ?
ALMA Memo 491 Does the ACA Need Phase Compensation ?
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ALMA 备忘录 491 ACA 是否需要相位补偿？
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
M. Holdaway
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作者：
M. Holdaway
我们分析了在1996 - 2001年期间从Chajnantor的相位监测数据，并推断出的相位波动水平，将看到1030米，典型的基线长度的阿塔卡马紧凑型阵列（ACA）。在10-30 m基线上，快速切换相位补偿将是无用的，但水汽辐射测量（WVR）可以稍微改善相位稳定度。我们考虑相位误差对成像和通量尺度的影响，并确定（a）ACA将需要动态调度以满足阿尔马科学目标，（B）给定动态调度，ACA将可能不需要任何种类的主动相位校正，例如WVR，以及（c）通过允许在具有最低不透明度和低于最佳相位稳定性的条件期间进行高频ACA观测，WVR可以增加ACA的效率，特别是对于高频观测，并且可能在成本效益的基础上被证明是合理的。我们希望在ACA上进行相位校准的另一个原因是，12 - 7 m的碟形天线无法在合理的时间内校准到所需的精度。为了精确校准，我们需要将7 m碟与专用于ACA的4个12 m碟相关联，或者甚至更好地与完整的阿尔马阵列相关联。如果我们与四个附近的12米碟形天线相关，我们不需要ACA天线上的相位补偿，但如果我们计划与全阿尔马相关，我们绝对需要WVR和快速切换能力。
We analyze the phase monitor data from Chajnantor over the period 1996 2001 and infer the level of phase fluctuations that would be seen on 1030 m, typical baseline lengths for the Atacama Compact Array (ACA). On baselines of 10-30 m, fast switching phase compensation will be useless, but water vapor radiometry (WVR) could improve the phase stability marginally. We consider the effects of phase errors on imaging and on the flux scale, and determine that (a) the ACA will require dynamic scheduling in order to meet the ALMA scientific objectives, (b) given dynamic scheduling, the ACA will likely not require any sort of active phase correction such as WVR, and (c) by permitting high frequency ACA observations during conditions with the lowest opacities and less than optimal phase stability, WVRs could increase the ACA’s efficiency, especially for high frequency observations, and can probably be justified on a cost-benefit basis. There is another reason why we would want phase calibration on the ACA – the 12 7 m dishes cannot calibrate themselves to the required accuracy in a reasonable amount of time. In order to calibrate accurately, we need to correlate the 7 m dishes with the four 12 m dishes dedicated to the ACA, or even better, with the full ALMA array. If we are correlating with the four nearby 12 m dishes, we do not need phase compensation on the ACA antennas, but if we plan to correlate with the full ALMA, we absolutely need WVR and fast switching capability.