研究結果顯示，NavPod 可在適當的品質控管下支援特殊事件的快速觀測，並具備擴充為區域固定式電離層監測網的潛力。然而，絕對 VTEC 仍可能受到接收機偏差、薄殼模型、觀測環境及背景產品解析度限制，還有長期運作品質與多站空間反演能力亦有待進一步驗證。本研究完成了由硬體建置、資料記錄與回傳，到 TEC 解算及事件分析的整合架構，為低成本、高彈性的區域電離層觀測提供一項可持續擴充的實作基礎。;Global Navigation Satellite System (GNSS) signals are affected by free electrons as they propagate through the ionosphere. Dual-frequency GNSS observations can therefore be used to retrieve total electron content (TEC) and monitor ionospheric disturbances. However， the high cost and limited deployment flexibility of conventional geodetic-grade receivers constrain rapid observations of transient events and the expansion of regional monitoring networks. This study develops NavPod， a low-cost and portable GNSS-based ionospheric observation system. NavPod integrates a dual-frequency GNSS receiver， a single-board computer， automated data logging， remote data transfer， and server-side processing. Two generations of the system were developed to support both short-term mobile deployment and long-term fixed-site monitoring.
A processing framework was also established to derive TEC products from raw GNSS observations. The procedure includes observation-time reconstruction， cycle-slip detection and arc segmentation， carrier-phase leveling， satellite and receiver hardware-bias treatment， satellite-geometry calculation， and thin-shell mapping. Two product levels were defined: relative TEC variations for event-based analysis and absolute station VTEC products for long-term monitoring. The first-generation NavPod systems were deployed at two stations within the path of totality during the 8 April 2024 North American total solar eclipse. Both stations recorded a distinct decrease in VTEC during the eclipse. The temporal difference between the two stations was consistent with the southwest-to-northeast motion of the lunar shadow， while ionospheric pierce-point distributions and comparison with a co-located high-grade receiver supported the plausibility of the observed variations. The second-generation systems were deployed at five fixed sites in Chiayi， Taiwan. Remote synchronization and server-side processing demonstrated the capability to continuously produce raw GNSS observations and TEC products. Product reliability was examined through diurnal behavior， interstation consistency， and residual analysis. Signal-strength observations were additionally used to calculate a $C/N_0$-derived amplitude-variation metric and establish a preliminary procedure for screening candidate disturbances and estimating interstation time delays.
The results demonstrate that， with appropriate quality control， NavPod can support rapid observations of transient ionospheric events and has the potential to form a regional long-term monitoring network. Nevertheless， absolute VTEC retrieval remains affected by receiver biases， thin-shell assumptions， local observation environments， and the resolution of background products. Further validation is also required for long-term operational reliability and multisite spatial inversion. This study establishes an integrated framework from instrument construction and data transmission to TEC retrieval and event analysis， providing a practical foundation for expandable， low-cost， and flexible regional ionospheric observations.
