## 3 Data and Processing  
### Data Acquisition  
Sentinel-2 optical images were used in this study to explore the lake ice displacement of Lake Khovsgol. These images are freely available to the public ([[https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)]([https://scihub.copernicus.eu/dhus/#/home](https://scihub.copernicus.eu/dhus/#/home)), accessed on 3 January 2021). The Sentinel-2 satellite consists of two satellites, i.e., Sentinel-2A and Sentinel-2B, which were launched in June 2015 and March 2017, respectively. The revisit periods are 10 days for a single satellite and 5 days for the satellite constellation. In high latitude regions where the image swaths from neighboring orbits have a dense overlap, the potential revisit time may be shorter than 5 days. Each Sentinel-2 optical image contains visible, near-infrared, and shortwave infrared parts with 13 bands of varied spatial resolutions, 4 bands with 10 m, 6 bands with 20 m, and 3 bands with 60 m. For details on Sentinel-2 image data, please refer to official ESA website descriptions ([[https://sentinels.copernicus.eu/web/sentinel/user-guides/sentinel-2-msi](https://sentinels.copernicus.eu/web/sentinel/user-guides/sentinel-2-msi)]([https://sentinels.copernicus.eu/web/sentinel/user-guides/sentinel-2-msi](https://sentinels.copernicus.eu/web/sentinel/user-guides/sentinel-2-msi)), accessed on 28 May 2021). A commonly used Sentinel-2 image in the Level-2A format, which has been corrected for terrain distortion, can cover a size of 100 \(\times\) 100 km\({}^{2}\) with orthorectified UTM or WGS84 projection. Their high temporal-spatial resolution, large-scale coverage, and open access data policy have made Sentinel-2 images ideal data sources to detect time series change of land [48] in comparison to other optical remote sensing images [49; 50] (e.g., Landsat and SPOT satellite images).  
This study collected all the Level-2A Sentinel-2 A/B optical acquisitions, spanning from 7 December 2020 to 17 June 2021. The optical images from this period are shown in Table 1. At each date, 4 acquisitions were merged into one image to cover the area of Lake Khovsgol. The percentages of cloud coverage for these images were within 0.36-60.9%. Cloud coverage is an inevitable problem of optical satellites handled with passive sensors that can directly lead to a loss of coherence between two images from different dates [51]. There is no consensus regarding which of the four 10 m resolution bands is the best band for pixel offset estimation. Given the radiometric characteristics of different bands for various surface targets, the authors of [52] thought that Sentinel-2 images of bands 4, 8, and 11 are more suitable for glacier offset tracking than other bands. In [50] the authors suggested that the pixel offset accuracy from band 8 Sentinel-2 images is slightly better than that of band 2, band 3, and band 4 Sentinel-2 images for land surface deformation monitoring. In this study, we chose band 8 as the experimental band for POT. Before pixel offset estimation, all Sentinel-2 images were preprocessed with the open-access Sentinel Application Platform (SNAP) for the image fusion and band extraction [53]. In addition, we collected local weather data from the global weather station located at 100.15\({}^{\circ}\) E and 50.433\({}^{\circ}\) N, as provided by the National Oceanic Atmospheric Administration (NOAA) ([[https://www.ncei.noaa.gov/maps/daily/](https://www.ncei.noaa.gov/maps/daily/)]([https://www.ncei.noaa.gov/maps/daily/](https://www.ncei.noaa.gov/maps/daily/)), accessed on 15 March 2021); see Figures 2 and 3.