LEAP：一种新的低频基阵方向相关电离层定标方案
LEAP: An Innovative Direction Dependent Ionospheric Calibration Scheme for Low Frequency Arrays
摘要：
SKA的雄心勃勃的科学目标需要一个校准大气传播误差的匹配能力，这会污染观测到的信号。我们展示了一个方案，用于纠正方向相关的电离层和仪器的相位效应在低频率和广泛的视野计划SKA-Low。它利用带宽拖影来滤除来自离轴方向的信号，从而允许在可见度域中测量基于方向的天线增益;通过对多个方向执行此操作，可以在宽视场范围内进行校准。这种策略消除了对全局天空模型的需要，因此所有方向都是独立的。我们使用MWA结果在88和154 MHz在各种天气条件下，以验证该技术的性能和适用性。我们的结论是，这种方法是合适的测量和校正的时间波动和方向依赖的空间电离层相位失真在很宽的范围内的尺度：大于和小于阵列的大小。后者最为棘手，对今后的文书构成重大挑战。此外，该方案是一个非常并行的过程，因为多个方向可以独立地同时处理。这是SKA的一个重要考虑因素，目前计划的架构是一个有限互连的计算岛。目前实施的算法和正在进行的发展进行了讨论。
英文摘要：
The ambitious scientific goals of the SKA require a matching capability for calibration of atmospheric propagation errors, which contaminate the observed signals. We demonstrate a scheme for correcting the direction-dependent ionospheric and instrumental phase effects at the low frequencies and with the wide fields of view planned for SKA-Low. It leverages bandwidth smearing, to filter-out signals from off-axis directions, allowing the measurement of the direction-dependent antenna-based gains in the visibility domain; by doing this towards multiple directions it is possible to calibrate across wide fields of view. This strategy removes the need for a global sky model, therefore all directions are independent. We use MWA results at 88 and 154 MHz under various weather conditions to characterise the performance and applicability of the technique. We conclude that this method is suitable to measure and correct for temporal fluctuations and direction-dependent spatial ionospheric phase distortions on a wide range of scales: both larger and smaller than the array size. The latter are the most intractable and pose a major challenge for future instruments. Moreover this scheme is an embarrassingly parallel process, as multiple directions can be processed independently and simultaneously. This is an important consideration for the SKA, where the current planned architecture is one of compute-islands with limited interconnects. Current implementation of the algorithm and on-going developments are discussed.
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