Abstract
The article presents a proposal to make simultaneous allowance for both ionospheric and tropospheric corrections in differential synthetic aperture radar interferometry (DInSAR) measurements. Atmospheric delay in the interferometric phase may cause the detection of terrain-surface changes to be impossible or significantly distorted. This fact remains of special importance in the case of surface changes that show limited amplitude and spatial range. Two areas were chosen to verify the validity of the proposed solution. The first area includes terrains affected by underground copper-ore mining activity (Poland), which shows high induced seismic activity. Mining tremors recorded in this area cause the terrain surface to locally subside. The authors analyzed three tremors that were recorded in 2016, 2017, and 2019. Each of the tremors exceeded a magnitude of Mw 4.0. The second area is located in the coastal region of Chile, in the Cardenal Caro province. In this case, the authors focused on a series of three earthquakes recorded on 11 March 2010. The strongest of the earthquakes was of Mw 7.0 magnitude. In the first case, calculations were based on obtained data from the Sentinel 1 satellites, and in the second case from the ALOS-1 satellite. It is demonstrated that simultaneous allowance for both the tropospheric and ionospheric corrections significantly improves the final results. The authors were also able to use the analyzed cases to demonstrate that implementation of the corrections does not have negative influence on the range and magnitude of local ground-surface deformations. At the same time, such implementation minimizes local displacement fluctuations and reduces displacement values in areas affected by deformations. The examples used in the article served to show that tropospheric correction is mainly responsible for global corrections (i.e., within the whole analyzed spatial range), while ionospheric correction reduces local fluctuations.
Highlights
Synthetic aperture radar interferometry (InSAR) allows the detection of ground-surface changes in a very wide range, from anthropogenic [1,2,3,4] and natural [5,6,7] events having limited spatial range and amplitude, to events having a wider, regional range [8,9,10]
We propose simultaneous allowance for tropospheric and ionospheric corrections in SAR calculations based on differential synthetic aperture radar interferometry (DInSAR)
In the GMTSAR environment, calculations using the DInSAR method were supplemented with an algorithm for calculating ionospheric correction based on the split-spectrum method [16], with filtering suggested by Fattahi [19]
Summary
Synthetic aperture radar interferometry (InSAR) allows the detection of ground-surface changes in a very wide range, from anthropogenic [1,2,3,4] and natural [5,6,7] events having limited spatial range and amplitude, to events having a wider, regional range [8,9,10]. The atmospheric screen significantly distorts obtained results and prevents reliable analysis of an event For these reasons, the time and spatial variability of atmospheric conditions has the most significant influence on the accuracy of measurements performed using InSAR methods. The influence of the ionosphere on satellites operating in C-band can be observed This is due to the fact that ionospheric distortions of microwave propagation cause additional group delay and phase lag in SAR images. Natural seismic events were chosen as an additional example: earthquakes that occurred in 2010 on the coast of Chile (the strongest of Mw 7.0 magnitude) This example was based on data from the ALOS-1 satellite, which operates in ScanSAR mode and in L-band
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