## 4 Results and Analysis
### Time Series Displacement for Ice Motion
During the second stage, most displacement values in the NS and EW components ranged from \(-12\) to \(12\) m (e.g., Figure 6(B1,B2,E1,E2,F1,F2,H1,H2)), and the rest showed small-displacement magnitudes (e.g., Figure 6(J1,J2,K1,K2)). That is to say that there were strong hydrological and hydrodynamic processes most of the time, but the lake ice movement was relatively mild sometimes. Moreover, these ice changes showed an obvious block feature in some result maps, and these ice blocks along the NS direction were divided by displacement gradients, e.g., the lake ice moved had two opposite directions (approximately 51.5\({}^{\circ}\) N); see Figure 6(B2,E2,H2,I2). Figure 6 also shows some small areas with losses of coherence. We know from the Sentinel 2 visible band that pixels are missing in Figure 6(E1-F2) due to cloud coverage. Additionally, the lake can be seen to be covered by white snow in Figure 6(P1-Q2). We speculate that the lake surface changed too quickly in short intervals due to constant snow, thus causing the pixels to be non-tracked. Moreover, the NS displacements were much larger than the EW displacements in most of the times in Figure 6.  
The third stage was the ice melt period, which began on 18 April 2021. In this stage, the movement monitoring of lake ice using POT was not satisfactory because the coherence was poor. As shown in Figure 7, we found no signals in most areas of the ice cover, and the displacement measurements of a few areas showed some abnormal values, except for the final disappearance of lake ice in June (Figure 7(F1,F2)) when we measured displacement values from about \(-1.2\) to \(-1.1\) m around the lakeshore. Moreover, the region's high cloud coverage in April and May led to some data unavailability; therefore, the observation period became longer. In addition to the loss of correlation due to cloud cover, the freeze-thaw cycle was a major reason for the loss of effectiveness of POT. During the day, melting snow and water filled up internal cracks in the lake ice, which froze at night again when the temperature was negative [19]. This process led to increased surface roughness and the scattering of the lake ice, which caused difficulties and errors in the pixel offset estimation. Figure 5: (**A1–D2**) represent the results of horizontal displacements of Lake Khovsgol in the EW and NS directions in the first stage. It is superimposed on 3 Arc-Second Global SRTM Digital Elevation Model (DEM) with 90 m resolution. The area marked by the dashed blue line in the figure is the missing signal due to cloud cover occlusion. Displacement values are positive for the eastern and northern directions. Figure 6: (**A1–Q2**) represent the horizontal displacement results of the surface of Lake Khovsgol in the EW and NS directions in the second stage. It is superimposed on 3 Arc-Second Global SRTM Digital Elevation Model (DEM) with 90 m resolution. The points P1–P5 and the dashed lines AA\({}^{\prime}\) and BB\({}^{\prime}\) in (**A1**) are used for the specific displacement analysis in Section 4.2. The area marked by the dashed blue line in the figure is the missing signal due to cloud cover occlusion. The red line marked is caused by the ice and snow mixture. Displacement values are positive for the eastern and northern directions.