**Abstract**

Sea ice monitoring is helpful to the research of the Arctic channels and climate environment. Through echo signal classification, re-tracking correction, and other techniques, data from the Cryosat-2 radar altimetry satellite between 2010 and 2020 facilitated the retrieval of Arctic sea-ice thickness and volume. The study subsequently analyzed the variations in the average thickness and volume of first-year ice and multi-year ice in the Arctic sea ice over the past decade. In the past decade, the volume of sea ice in the Arctic region fluctuates slightly. The multiyear ice changed greatly in 2013, while the first-year ice shows an increased rate of both winter growth and summer ablation. The presence of uncertainties arising from the fluctuations in sea ice density values and the intricate patterns of Arctic circulation might impart subtle biases in the measurements of sea ice thickness. However, the sea ice freeboard and thickness data inverted based on the Cryosat-2 data were validated by the data obtained through the Operation Ice Bridge (OIB), and the validation results indicated that they are correspondent.

**Keywords:** sea ice, Cryosat-2, the Arctic, thickness, volume

#### **1. Introduction**

As an indicator of the Arctic climate, the sea ice is affected by the climate change and reacts to global climate. It is an important indicator of global climate change research and a window to understanding the current situation and change trend of the Arctic environment. For a long time, limited by the harsh natural environment of the Arctic region, the Arctic sea ice observation is high cost and low efficiency. Therefore, it is difficult to realize the large-scale, multi-scale, and long-time series monitoring. With the rapid development of remote sensing technology, satellite altimetry has become an effective method to continuously obtain the accurate global thickness information on the sea ice [1]. The Earth Explorer Opportunity Mission-2 (CryoSat-2) satellite which launched in April 2010, with full coverage of the Arctic region and a

centimeter-level precision [2], could meet the need for long-term monitoring of the sea ice thickness.

At the same time, the theoretical method of the altimetry satellite inversion of the sea ice thickness has also attracted the attention of many researchers. In 2003, the sea ice thickness in the 40°N 81.5°N range was retrieved by Peacock, Laxon et al. based on the Earth Resources Satellite-1 altimetry satellite [3, 4]. As mentioned in the articles [3, 4], the sea ice was distinguished from the water according to the pulse peaks and backscattering coefficients of the radar echo signals. After that, the echo signals are corrected by the re-tracking algorithm to calculate the elevation of the subsatellite point and obtain the elevation difference between the sea ice and the surrounding seawater namely sea ice freeboard. Then, the sea ice thickness is estimated based on the static equilibrium state of the sea ice, and some parameters such as snow density and snow depth as well. Currently, the echo signals classification [5–8], retracking correction algorithm [9–12], and sea ice thickness inversion model parameters [13–16] have become hot issues in sea ice thickness monitoring.

To study the changes in the Arctic sea ice thickness between 2010 and 2019, this paper selects the following data such as the CryoSat-2 data with high accuracy and full coverage, the MASAM2 sea ice density product with daily update of the 4 km resolution grid, the OSI SAF (Ocean and Sea Ice Satellite Application Facility) daily update product of the sea ice type with 10 km resolution grids, the UCL13 MSS (Mean Sea Surface model of the University College London 2013) and the ice snow thickness data with the 24 km resolution grids of daily update produced by the Canadian Meteorological Center. With the above data, this paper analyzes the variation characteristics of the sea ice thickness in recent years, which could provide the data basis for the change trend research of the large-scale sea ice thickness in the Arctic region.
