Estimation of Arctic Winter Snow Depth, Sea Ice Thickness and Bulk Density, and Ice Freeboard by Combining CryoSat-2, AVHRR, and AMSR Measurements

Abstract

Information on snow depth on sea ice and bulk sea ice density is required to convert CryoSat-2 radar freeboard (hf) into sea ice thickness (SIT). It is difficult to obtain their information on an Arctic basin scale; therefore, most CryoSat-2 SIT products largely rely on the distributions of snow depth and bulk sea ice density derived from parameterizations, which are based on sea ice type and climatological values. Several observational studies have found that the distributions of parameterized variables are inaccurate compared to the actual distributions. This study aims to develop a new type of retrieval algorithm for snow depth, SIT and bulk density, and ice freeboard in the Arctic winter by synergizing active CryoSat-2 with passive microwave and infrared measurements. Two parameterizations for the snow-ice thickness ratio and bulk sea ice density were combined with the hydrostatic balance and radar wave speed correction equations. Consequently, solutions for the four target variables were obtained and applied to different CryoSat-2 hf, derived from empirical and waveform-fitting retracker algorithms. The retrieved thickness-related parameters based on hf from the lognormal waveform-fitting retracker algorithm showed good agreement with the airborne snow depth, total freeboard, and mooring ice draft measurements. The retrieved multiyear sea ice bulk density was significantly higher than the value of 882 kg m -3 , which was used in the previous density parameterization, showing a higher agreement with values from in-situ measurements. The spatial and interannual variabilities of SIT increased when the results from this study were compared with those based on previous parameterizations.

Seasonal evolution and parameterization of Arctic sea ice bulk density: results from the MOSAiC expedition and ICESat-2/ATLAS

“…For the other bivariate parameter, the ice freeboard-to-total freeboard ratio also performed well, exceeding all univariate parameters, with R 2 and RMSE values of 0.93 (P < 0.001) and 4.76 kg m −3 , respectively. The strong linear relationship between the two bivariate parameters and IBD further indicates that the relative proportions of the above-and below-water components of sea ice, as well as the relative proportions of snow cover and ice freeboard, are potentially significant indicators of IBD, supporting previous suggestions (Alexandrov et al, 2010;Shi et al, 2023).…”

“…By contrast, given the significant disparity in ice density and porosity between exposed and submerged MYI, the MYI density of A10 (882 ± 23 kg m −3 ) was calculated by considering the ice portions above and below the sea surface and weighted by the corresponding reference IBDs (Timco and Frederking, 1996;Pustogvar and Kulyakhtin, 2016). However, Shi et al (2023) have recently argued that the reference IBD of MYI above the sea surface, defined in A10 as only 550 kg m −3 , does not accurately represent the properties of MYI, highlighting the potential uncertainties of the A10 approach. Furthermore, several studies have examined the relationship between IBD and other sea ice parameters, with the goal of developing IBD parameterizations.…”