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Correcting the signal delay caused by electromagnetic waves passing through the atmosphere is crucial in InSAR. Atmospheric delays are significant enough to obscure the true deformation signal, making it difficult for InSAR to detect deformation signals at the millimetre scale. Therefore, it is imperative to mitigate atmospheric interference appropriately. To interpolate sparse GNSS networks and capture small-scale atmospheric delays, this study presents an enhanced method for constructing an atmospheric correction model based on GNSS Zenith Total Delay (ZTD) and its horizontal gradient, which is integrated within a predefined window. To validate the effectiveness of the improved model, we applied it to 27 InSAR short-time and short-spatial baseline unwrapped interferograms. These interferograms are composed of images observed by the Sentinel-1A satellite from January to December 2022 in Southern California. The corrective impact of the enhanced model is also compared against that of the initial inversion model and GACOS to confirm the viability of the approach. Results of the evaluation, considering root mean square error (RMSE), standard deviation (STD), and the correlation between phase and elevation, indicate that our enhanced method reduces correction errors by 35.10%, 20.05%, and 63.52%, respectively, compared to GACOS. Compared to the initial model, these reductions are 58.19%, 57.23%, and 4.34%, respectively. By integrating the outcomes from all three evaluation methods and analysing the corrected images, our enhanced model effectively resolves the inconsistency in correction effects resulting from the spatial variability of atmospheric delay. Moreover, incorporating the horizontal gradient in the inversion method has proven effective in capturing small-scale atmospheric delay signals. This highlights the feasibility and benefits of our enhanced model. [ABSTRACT FROM AUTHOR]

The Hunga Tonga‐Hunga Ha'apai (hereafter HTHH) submarine volcano erupted at 04:14:45 UT on 15 January 2022, causing ionospheric disturbances. This paper uses carrier phase observations from GNSS tracking stations in New Zealand and Australia to calculate the vertical total electron content. At 06:10, the ground‐based GNSS tracking station in New Zealand observes a maximum amplitude of 2.26 TECU anomaly caused by a mesoscale traveling ionospheric disturbance (MSTID) with a wavelength of 200–250 km, a period of 6–13 min, and a maximum propagation velocity of 330 m/s. The anomaly developed with time along the north‐south island direction toward the south island and lasted for about three and a half hours, with the ionosphere returning to pre‐eruption levels after 09:50, indicating a correlation between ionospheric activity and volcanic eruption. An ionospheric anomaly caused by an MSTID was also observed off the east coast of Australia around 08:11, with a maximum amplitude of 3.17 TECU and a maximum propagation velocity of 356 m/s. The ionospheric anomaly in Australia spreads out in a plane. In the process of propagation, it continuously impacts the area it passes through, and the entire anomaly process lasts for more than 7 hr. Still, the anomalous propagation velocities are more significant than in New Zealand, indicating that the Lamb waves excited by the eruption of the HTHH submarine volcano are directional in propagation speed; westward travels faster than southward. This finding will provide more references for scholars to study the mechanism and characteristics of anomaly propagation. Plain Language Summary: This paper reports on the Hunga Tonga‐Hunga Ha'apai submarine volcanic eruption event at Tonga on 15 January 2022, which caused air pressure waves in the form of Lamb waves to propagate to ionospheric heights and caused traveling ionospheric disturbances. Analysis of the filtered total electron content in the ionosphere using dense GNSS tracking stations in Australia and New Zealand revealed large‐scale, intense ionospheric disturbances. The propagation of the anomaly is also directional, with the New Zealand ionospheric anomaly initially propagating from north to south in a ripple pattern with a maximum mesoscale traveling ionospheric disturbance (MSTID) propagation velocity of ∼330 m/s. The impact of Lamb waves on the ionosphere in Australia is more pronounced, with the disturbance unfolding in a faceted pattern from east to west for up to 7 hr, during which the maximum MSTID propagation velocity is ∼356 m/s. In addition, the anomaly is affected by small‐amplitude gravity waves and excites multiple ionospheric disturbance phenomena during its propagation in both locations. This result confirms the natural phenomenon of ionospheric disturbances induced by extreme natural hazards and shows that severe explosive events can have a lasting and far‐reaching impact on the ionosphere. Key Points: Evidence of widespread traveling ionospheric disturbances caused by volcanic eruptionsThe propagation of the anomaly is directional, propagating westward at a greater rate than southwardSmall‐scale gravity waves have caused multiple transient ionospheric disturbances in both New Zealand and Australia [ABSTRACT FROM AUTHOR]