Ocean surface radial velocities (RVLs) derived from the Sentinel‐1 A/B Interferomic Wide (IW) mode Doppler frequency shift observations are regularly acquired over the Norwegian coastal zone. These data can be used to complement existing ocean observation systems with high‐resolution (up to 1.5 × 1.5 km) spatial ocean surface current (OSC) maps. In this study, Sentinel‐1 IW Level 2 OSC retrievals were obtained from 2 months (October–November 2017) of raw Doppler shift observations acquired over the Norwegian Coastal Current (NCC). The results were evaluated using coastal high‐frequency radar (HFR) and Lagrangian ocean surface drifter observations. The analysis shows that distinct patterns of the NCC, with range directed currents reaching up to 0.7 m/s, can be detected in the SAR data. The mean bias between Synthetic Aperture Radar (SAR) and HFR observations was −0.08 m/s and the root mean square deviation (RMSD) was 0.25 m/s. In comparison, the agreement between the SAR‐derived OSC and the trajectories from Lagrangian surface drifters showed a mean bias of 0.02 m/s and an RMSD of 0.24 m/s. The accuracy of the SAR OSC retrievals rely on precise wind‐wave bias correction. Hence, the accuracy of the model wind field (speed and direction) is crucial. The sea state contribution must also be taken into account during the bias correction. A typical required accuracy of the OSC velocity is on the order of 0.1 m/s. Therefore, the comparisons demonstrate that the use of SAR for OSC retrieval is promising.

The Doppler frequency shift acquired by Synthetic Aperture Radar (SAR) contains information about ocean surface motion induced by waves and the underlying ocean currents in the radar range direction. An accurate estimate of the wave‐induced contribution is therefore required to derive a reliable estimation of the ocean surface current. In this study, we developed an empirical model for estimating the wave‐induced Doppler shift based on Sentinel‐1B Wave Mode (WV) Level 2 Ocean products acquired from December 2017 to January 2018 collocated with wind field from ECMWF and wavefield from WAVEWATCH III. We found that the relationship between the wind field at 10 m height and the Doppler shift from Sentinel‐1 is in agreement with previous findings based on ASAR observations. Retraining of the conventional CDOP model for the Sentinel‐1 observations (CDOP‐S) yields distinct improvements. We speculate that the improvement is due to different sensor properties and hence biases in the data. Moreover, combing wave and wind information into the model yield considerable improvements especially for the Southern Ocean and the North Pacific. Given accurate wave bias correction, the ocean surface radial velocity maps based on 2 months of Sentinel‐1 acquisitions agree with ocean surface current climatology derived from multiyear drifter observations. This suggests that Sentinel‐1 Doppler shift observations can be used to study ocean surface currents with 20 km spatial resolutions at a monthly time scale.

Arctic climate change has already resulted in amplified and accelerated regional warming, or the Arctic amplification. Satellite observations have captured this climate phenomenon in its development and in sufficient spatial details. As such, these observations have been—and still are—indispensable for monitoring of the amplification in this remote and inhospitable region, which is sparsely covered with ground observations. This study synthesizes the key contributions of satellite observations into an understanding and characterization of the amplification. The study reveals that the satellites were able to capture a number of important environmental transitions in the region that both precede and follow the emergence of the apparent amplification. Among those transitions, we find a rapid decline in the multiyear sea ice and subsequent changes in the surface radiation balance. Satellites have witnessed the impact of the amplification on phytoplankton and vegetation productivity as well as on human activity and infrastructure. Satellite missions of the European Space Agency (ESA) are increasingly contributing to amplification monitoring and assessment. The ESA Climate Change Initiative has become an essential provider of long-term climatic-quality remote-sensing data products for essential climate variables. Still, such synthesis has found that additional efforts are needed to improve cross-sensor calibrations and retrieval algorithms and to reduce uncertainties. As the amplification is set to continue into the 21st century, a new generation of satellite instruments with improved revisiting time and spectral and spatial resolutions are in high demand in both research and stakeholders’ communities.