Ionospheric irregularities can adversely affect the performance of Global Navigation Satellite System (GNSS). However, this opens the possibility of using GNSS as an effective ionospheric remote sensing tool. Despite ionospheric monitoring has been undertaken for decades, these irregularities in multiple spatial and temporal scales are still not fully understood. This paper reviews Virginia Tech’s recent studies on multi-scale ionospheric irregularities using ground-based and space-based GNSS observations. First, the relevant background of ionospheric irregularities and their impact on GNSS signals is reviewed. Next, three topics of ground-based observations of ionospheric irregularities for which GNSS and other ground-based techniques are used simultaneously are reviewed. Both passive and active measurements in high-latitude regions are covered. Modelling and observations in mid-latitude regions are considered as well. Emphasis is placed on the increased capability of assessing the multi-scale nature of ionospheric irregularities using other traditional techniques (e.g., radar, magnetometer, high frequency receivers) as well as GNSS observations (e.g., Total-Electron-Content or TEC, scintillation). Besides ground-based observations, recent advances in GNSS space-based ionospheric measurements are briefly reviewed. Finally, a new space-based ionospheric observation technique using GNSS-based spacecraft formation flying and a differential TEC method is demonstrated using the newly developed Virginia Tech Formation Flying Testbed (VTFFTB). Based on multi-constellation multi-band GNSS, the VTFFTB has been developed into a hardware-in-the-loop simulation testbed with external high-fidelity global ionospheric model(s) for 3-satellite formation flying, which can potentially be used for new multi-scale ionospheric measurement mission design.

中文翻译：

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使用地基和天基 GNSS 观测表征多尺度电离层不规则性

电离层的不规则性会对全球导航卫星系统 (GNSS) 的性能产生不利影响。然而，这开启了使用 GNSS 作为有效电离层遥感工具的可能性。尽管电离层监测已经进行了几十年，但这些在多个时空尺度上的不规则性仍然没有被完全理解。本文回顾了弗吉尼亚理工大学最近使用地基和空基 GNSS 观测对多尺度电离层不规则性的研究。首先，回顾了电离层不规则性的相关背景及其对 GNSS 信号的影响。接下来，回顾了同时使用 GNSS 和其他地面技术的电离层不规则性地面观测的三个主题。涵盖了高纬度地区的被动和主动测量。中纬度地区的建模和观测也被考虑在内。重点放在使用其他传统技术（例如，雷达、磁力计、高频接收器）以及 GNSS 观测（例如，总电子含量或 TEC、闪烁）评估电离层不规则性的多尺度性质的能力增强. 除了地面观测外，还简要回顾了 GNSS 天基电离层测量的最新进展。最后，使用新开发的弗吉尼亚理工大学编队飞行试验台 (VTFFTB) 展示了一种使用基于 GNSS 的航天器编队飞行和差分 TEC 方法的新天基电离层观测技术。基于多星座多频段GNSS，