Yunmeng Cao
Institute: GNS Science
Title: InSAR Scientist
Country/Region: New Zealand
Period: 2023/07/03-2023/9/29
Theme: Space geodetic analysis of volcanic activities over the Taupo Volcanic Zone, New Zealand
Host: Yosuke AOKI
Introduction: Yunmeng Cao is a satellite-geodesy researcher and currently working with the Geodynamics team in GNS Science, New Zealand. His work focusses on using satellite radar technology to detect Earth surface’s displacements that are associated with a wide range of geophysical and geotechnical processes, such as seismic- and volcanic-activities, earthquake- and climate-induced landslides, infrastructure damages, and natural hazards caused surface changes. He explores advanced approaches to improve satellite geodesy for better geoscience applications, and he also develops a couple of open-source softwares for processing SAR/InSAR data precisely, automatically, and rapidly, that are used across the satellite geodesy community.

Research Report:
Progress report
Space geodetic analysis of volcanic activities over the Taupo Volcanic Zone, New Zealand
Yunmeng Cao1, Yosuke Aoki2
GNS Science, Lower Hutt, New Zealand1
The University of Tokyo, Earthquake Research Institute, Tokyo2
The Taupo Volcanic Zone (TVZ) based in the North Island of New Zealand is an area of supervolcanoes with about 300-km-long and 60-km-wide, formed due to the back-arc rifting associated with subduction of the Pacific Plate beneath the Australian Plate. The TVZ is a rifted arc with current extension rate of about 8-15 mm/yr, and its longitudinally segmented nature, high thermal flux and voluminous rhyolitic volcanism make it unique on Earth. Although numerous papers have been presented on the structure, history and evolution of the TVZ, our understanding is still incomplete, and many interpretations require revision and continued investigation. As a result, it is important to monitor spatio-temporal evolutions of the ground displacements of TVZ, particularly with high-spatial resolution.
At this stage, we mainly focus on collecting datasets and doing some initial processes. We acquired both the ScanSAR- (2 tracks including ascending and descending) and Stripmap- (2 tracks cover the lake including ascending and descending) modes of ALOS-2 datasets over TVZ, as well as the C-band Sentinel-1 datasets (2 tracks including ascending and descending), during a period from 2015 to 2023. We did the time-series analysis of both the ALOS-2 and Sentinel-1 data, and evaluated/compared the quality of the results derived from these two Satellite with different wavelengths. Figure 1 shows the averaged InSAR coherence of ALOS-2 (example from ScanSAR) and Sentinel-1 during 2015 to 2022. We can find that the quality of ALOS-2 InSAR is much better than that of Sentinel-1. Low coherence affects both the interferometric phases and the unwrapped results, which will largely limit the quality of time-series analysis over large areas, as the decorrelation noise caused unwrapping errors would be propagated through space, e.g., the quality of time-series would decrease with the increase of the distance from the reference pixel to the pixel of interest.
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Fiscal Year: 2023