What exactly do InSAR analysts do, and how does this work assist those monitoring the same assets from the ground?
The work of Interferometric Synthetic Aperture Radar (InSAR) analysts involve several steps when handling data, including data preparation, the generation of interferograms, phase unwrapping, and interpretation. Before any analysing can occur, analysts must acquire the data. InSAR analysts obtain this data from satellite missions that provide interferometric capabilities such as Sentinel-1. These satellites capture multiple SAR images of the same area over different time periods.
The acquired data then undergoes preprocessing to remove noise and correct geometric distortions. Steps involved in this process could include radiometric calibration, speckle filtering, and orthorectification for subsequent analysis. Once this process is complete, the generation of interferograms is possible.
In order to process interferograms, the analyst must select pairs of SAR images acquired at different times for processing. That’s why experts sometimes refer to InSAR as DInSAR (Differential InSAR). By calculating the phase difference between two SAR images, we can find the movement of the Earth's surface. Analysts complete this process pixel by pixel for two different dates.
Interferograms contain “wrapped” phase values, which limits the phase measurements to a range of -π to +π. Researchers perform phase unwrapping to remove these phase ambiguities and obtain the actual displacement values. This means finding the right number of 2π cycles to add or subtract from each pixel. This helps create a smooth unwrapped phase map.
These unwrapped values are converted into elevation information. To do this, the analysts use the distance between satellites and their orbit information. They calculate the topographical part of the phase. What emerges from this process is a Digital Elevation Model (DEM) that represents the height of a surface.
From a detailed study of the interferograms and derived DEM, analysts can identify and quantify surface deformations. This includes detecting and measuring deformations such as subsidence, uplift, and lateral movements in infrastructure or natural features.
InSAR analysts often assess a series of interferograms acquired over time to track deformation trends. This lets them look at how fast deformities change over time. It gives insight into the structure's stability and health.
Finally, researchers compile these findings in reports and maps. They show the detected deformities, their size, and their possible effects on infrastructure. Analysts communicate their results to stakeholders, such as infrastructure managers, engineers, or decision makers who can take appropriate actions for maintenance or mitigation.
InSAR enables a wide area coverage of infrastructure networks, allowing for the monitoring of large regions and extensive networks simultaneously. This work complements localized and targeted measurements performed by in-situ monitoring operatives.
InSAR allows for the early detection of infrastructure defects on a regional scale. InSAR analysis can identify areas of potential concern, guiding in-situ monitoring efforts to specific locations that require detailed inspections of further investigations.
Moreover, researchers can use in-situ monitoring data to validate and calibrate the results obtained through InSAR analytical methods. By comparing the measurements acquired on-site with the remote sensing data, we can address any discrepancies.
Finally, we can combine in-situ monitoring and InSAR data. This will give us a complete view of the infrastructure's condition. Combining the strengths of both approaches can lead to a more complete understanding of defects, deformations, and risk. The integration of multiple data sources enhances the accuracy, reliability, and effectiveness of infrastructure monitoring and management.
Want to learn more about how InSAR works as am infrastructure monitoring tool? Find out in this article...
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