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  • Writer's pictureGeofem

Correcting Atmospheric Effects by Preprocessing SAR Images

Updated: Jul 5

In IAM News episode 15, Iphigenia mentioned how atmospheric effects can introduce errors into the results of interferograms. Those effects can be accounted for by preprocessing satellite SAR images before interferometric analysis. Let’s take a closer look at this topic today.

The removal of the Atmospheric Phase Screen or APS as it is known, represents the spatial distribution of phase delays as a result of the atmosphere that contributes to errors in the interferometric phase. Removing or minimizing the APS is crucial for accurately measuring ground deformations.

Persistent Scatterer Interferometry (PSI) is a technique that identifies and exploits radar targets (persistent scatterers) that remain coherent in terms of their ability to backscatter radar waves over time. These targets, which include buildings and other stable structures, are used to estimate the atmospheric phase delays. This process begins with the identification of potential persistent scatterers based on their stability in radar scattering over multiple acquisitions. Secondly, the interferometric phase information over time for each persistent scatterer is extracted. From here, the APS can be estimated by modelling the time-dependent phase information and subtracting the estimated APS will produce the corrected phase.

Of course, there are some challenges with mitigating the effects of atmospheric factors in interferometry. Atmospheric effects are often nonlinear and can vary spatially and temporally, posing challenges for accurate modelling and removal. Moreover, changes in atmospheric conditions over time may lead to temporal decorrelation, making it difficult to accurately estimate the APS. Using data that extend to a minimum of a one-year period can better describe the atmospheric effects, resulting in more accurate measurements of displacement.

In summary, the Atmospheric Phase Screen removal process, whether through the application of PSI, SBAS, or a combination of methods, plays a crucial role in mitigating the impact of atmospheric effects on interferometric phase in SAR interferometry. These techniques aim to estimate and remove the spatial and temporal vacations in atmospheric delays, resulting in more accurate and reliable ground deformation measurements.

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