评估电离层对LOFAR十米波巡天图像质量的影响
Assessing ionospheric effects on image quality in the LOFAR Decametre Sky Survey
- ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）
- Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究利用LOFAR十米波巡天数据，通过相位校准推导电离层指标，揭示空间电离层结构是限制图像质量的主导因素，并提供诊断与预测方法。
AI中文摘要：
地球电离层是十米波波长下高角分辨率成像的主要限制因素。其快速变化且与方向相关的相位误差会使源散焦、降低恢复的通量密度，并导致图像质量在不同视场间产生强烈差异。我们利用LOFAR十米波巡天（LoDeSS）中在三种不同电离层条件下观测到的三个重叠指向来研究这些效应。通过使用一个亮源的相位校准解，我们推导了空间衍射尺度、时间去相关时间以及方向相关校准解在残余相位误差变得显著之前可被转移的角尺度。这些指标反映在最终图像质量中。电离层相位结构最弱的视场具有最锐利的致密源和最可靠的通量密度尺度，而相位结构最强的视场则表现出显著的源展宽和通量密度损失。比较表明，空间电离层结构是这些观测中的主导限制因素。因此，由校准导出的电离层指标为诊断和预测十米波巡天数据中的图像质量变化提供了一种实用方法。
英文摘要：
The terrestrial ionosphere is a major limitation for high angular resolution imaging at decametre wavelengths. Its rapidly varying and direction-dependent phase errors can defocus sources, reduce recovered flux densities, and produce strong field-to-field variations in image quality. We investigate these effects using three overlapping pointings from the LOFAR Decametre Sky Survey (LoDeSS), observed under different ionospheric conditions. Using phase-calibration solutions on a bright source, we derive the spatial diffractive scale, the temporal decorrelation time, and the angular scale over which direction-dependent calibration solutions can be transferred before residual phase errors become significant. These metrics are reflected in the final image quality. The field with the weakest ionospheric phase structure has the sharpest compact sources and the most reliable flux-density scale, while the field with the strongest phase structure shows substantial source broadening and flux-density loss. The comparison indicates that spatial ionospheric structure is the dominant limitation in these observations. Calibration-derived ionospheric metrics, therefore, provide a practical way to diagnose and predict image-quality variations in decametre survey data.
