An advanced methodology for the detection and quantification of the ice-free period in the Arctic coastal zone is proposed. Ice-free period (IFP) dynamics is analyzed in the Kara Sea coastal zone near "Marresalya" and "Amderma" stations using long-term satellite data about sea ice concentrations. In a new method an advanced approach for defining the IFP characteristics (starting/ending dates and duration) was applied in addition to the conventional use of 15% sea ice concentration threshold. We provide estimates of the mean statistics and linear trends in the IFP characteristics using three long-term satellite-based sea ice concentration datasets: OSI SAF, NSIDC, JAXA and compare them to the estimates based upon direct observations on stations. Mean IFP durations and ending dates as well as linear trends derived from satellite data show a close comparability with observations with differences ranging within 2-7 days for IFP durations and within 0.01-0.05 days/year for IFP ending date trends. At the same time, strong deviations were found for both mean and long-term trends of the IFP starting dates, specifically showing negative trends in the satellite-derived starting dates which is not confirmed by observations. This results in a moderate agreement on trend estimates in IFP durations between satellite data and observations, while the mean characteristics are in a very good agreement and implies the necessity of more careful look onto representativeness of satellite data in the near-coastal zone during the onset season.