Saline-Soil Deformation Extraction Based on an Improved Time-Series InSAR Approach

Abstract

Significant seasonal fluctuations could occur in the regional scattering characteristics and surface deformation of saline soil, and cause decorrelation, which limits the application of the conventional time-series InSAR (TS-InSAR). For extending the saline-soil deformation monitoring capability, this paper presents an improved TS-InSAR approach, based on the interferometric coherence statistics and high-coherence interferogram refinement. By constructing a network of the refined interferograms, high-accuracy ground deformation can be extracted through the weighted least square estimation and the coherent target refinement. To extract the high-accuracy deformation of a representative saline soil area in the Qarhan Salt Lake, 119 C-band Sentinel-1A images collected between May 2015 and May 2020 are selected as the data source. Subsequently, 845 refined interferograms are selected from all possible interferograms to conduct the network inversion, based on the related thresholds (the temporal baseline < 49 days, the average spatial coherences > 0.5, respectively). Compared with the conventional TS-InSAR measurements, both the accuracy and reliability of the extracted deformation results of the saline soil increased dramatically. Furthermore, the testing results indicate that the improved TS-InSAR method has advantages on the deformation extraction in the saline soil region, and is adaptive to reflecting the typical seasonal variations of the saline soil.

Deformation monitoring and influence factor analysis of expressway over strong saline soil based on an advanced multi-temporal InSAR technique

“…But in the dry season, the high coherences appear again between November and the next April or May. This result proves that the interferometric coherences decrease dramatically due to the increase in precipitation from the dry season to the rainy season (Rui et al, 2021;Xiang et al, 2021;Xiang et al, 2022). However, thousands of average interferometric coherence coefficients are needed for the calculation for further analysis; such a heavy computation requirement is not suitable for long-term monitoring.…”

“…The previous studies found that the interferometric coherence coefficients in these similar saline mudflat areas have seasonal changes. As shown in Figure 4 (by setting the temporal baseline threshold for 400 days that includes a whole year and the perpendicular spatial baseline threshold for 200 m, a total of 2,921 interferograms are formed with 119 Sentinel-1A images acquired from 2015 to 2020) (Xiang et al, 2021), in the rainy season, the high interferometric coherences of interferograms mainly occur between June and November and disappear dramatically after November. But in the dry season, the high coherences appear again between November and the next April or May.…”

“…For the conventional MT-InSAR (PS-InSAR TM and SBAS-InSAR), it is hard to obtain the DTs maximally in the study area. Because of the interferograms, coherence seasonal characteristics are affected by kinds of external environmental factors such as precipitation and temperature, we performed interferogram seasonal filtering to optimize the network and select the DTs through a strict temporal coherence threshold (0.75) based on the conventional SBAS-InSAR (Rui et al, 2021;Xiang et al, 2021;Xiang et al, 2022). Whereafter, the time series deformation model based on the Poisson curve (PC) is applied to obtain high-precision time series deformation results of the DTs (Ming-hua et al, 2005;Zhu and Zhou, 2009;Yang et al, 2016;Jianjun et al, 2017;Zhu et al, 2021).…”

“…After that, they find that the interferometric coherences are highly correlated with the precipitation. Finally, the interferograms with average spatial coherence higher than 0.5 are refined as the available interferograms (Hu et al, 2017;Rui et al, 2021;Xiang et al, 2021;Xiang et al, 2022). Such heavy computation requirements are not suitable for long-term monitoring.…”

“…FIGURE 4Average interferometric coherence coefficients from 2015 to 2020, the vertical axis represents the period of the primary images and the horizontal axis represents the period of the secondary images. The color values of pixels represent the ASC of the interferograms(Xiang et al, 2021).…”