An efficient feedback calibration algorithm for direct imaging radio telescopes
An efficient feedback calibration algorithm for direct imaging radio telescopes
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DOI：
10.1093/mnras/stx1512
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发表时间：
2016-03
影响因子：
4.8
通讯作者：
A. Beardsley;N. Thyagarajan;J. Bowman;M. Morales
中科院分区：
文献类型：
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作者：
A. Beardsley;N. Thyagarajan;J. Bowman;M. Morales
我们提出了电场并行成像校准（EPICal）算法，它解决了直接成像射电天文仪的快速校准方法的需求。直接成像涉及天线信号的空间快速傅立叶变换，减轻了无线电发射机中典型的计算瓶颈，并产生更温和的$\mathcal {O}（N_{\mathrm{ant}}^2）$缩放，其中$N_{\mathrm{ant}}$是阵列中天线的数量，$N_g$是成像分析中网格点的数量。这可以为由数百或数千个天线组成的下一代阵列节省数量级的计算成本。然而，由于天线信号在成像相关器中混合而不产生抖动，因此必须在成像之前应用增益校正，而不是在抖动后相关时应用。我们开发了EPICal算法，以快速形成增益解决方案，而不会形成vibrations。这种方法随着天线的数量而缩放，并且产生与来自vibration的结果相当的结果。我们使用模拟演示的EPICal技术和研究我们的增益解决方案的噪声特性，显示它们是类似的可视性为基础的解决方案在现实情况下。通过将EPICal应用于两秒钟的长波长阵列数据，与未校准的图像相比，我们实现了65%的动态范围改善，表明该算法是下一代仪器的有前途的解决方案。
We present the E-field Parallel Imaging Calibration (EPICal) algorithm, which addresses the need for a fast calibration method for direct imaging radio astronomy correlators. Direct imaging involves a spatial fast Fourier transform of antenna signals, alleviating an $\mathcal{O}(N_{\mathrm{ant}}^2)$ computational bottleneck typical in radio correlators, and yielding a more gentle $\mathcal{O}(N_g \log_2 N_g)$ scaling, where $N_{\mathrm{ant}}$ is the number of antennas in the array and $N_g$ is the number of grid points in the imaging analysis. This can save orders of magnitude in computation cost for next generation arrays consisting of hundreds or thousands of antennas. However, because antenna signals are mixed in the imaging correlator without creating visibilities, gain correction must be applied prior to imaging, rather than on visibilities post-correlation. We develop the EPICal algorithm to form gain solutions quickly and without ever forming visibilities. This method scales as the number of antennas, and produces results comparable to those from visibilities. We use simulations to demonstrate the EPICal technique and study the noise properties of our gain solutions, showing they are similar to visibility based solutions in realistic situations. By applying EPICal to two seconds of Long Wavelength Array data we achieve a 65% dynamic range improvement compared to uncalibrated images, showing this algorithm is a promising solution for next generation instruments.