The Copernicus Imaging Microwave Radiometer (CIMR) is currently being implemented by the European Space Agency (ESA) as a Copernicus Expansion Mission primarily designed to observe the Polar Regions in support of the Integrated European Policy for the Arctic. It is a conically scanning microwave radiometer with polarized channels centered at 1.414, 6.925, 10.65, 18.7, and 36.5 GHz and channel NEΔT between 0.2-0.7 K. A large rotating deployable mesh reflector will provide real-aperture resolutions ranging from 60 (1.4 GHz) to 5 km (36.5 GHz). To evaluate CIMR retrieval performance, a simplified end-to-end simulation of the mission has been carried out. The simulation includes important processes and input parameters, such as test geophysical datasets, forward models, an instrument simulator, and retrieval algorithms to derive the key mission geophysical products. The forward modeling is tested by producing Brightness Temperatures (TBs) from 4 global scenes. A comparison with current observations of the open ocean and sea ice at similar frequencies confirmed the realism of the simulations. The produced top-of-atmosphere TBs are converted to Antenna brightness Temperatures (TAs), taking into account the instrument design, and are then inverted to retrieve Sea Ice Concentration (SIC), Sea Surface Temperature (SST), and Sea Surface Salinity (SSS). Evaluating the retrieval performance showed that the simulated CIMR instrument can provide SST, SSS, and SIC measurements with precisions and spatial resolutions conforming with the mission requirements. The evaluation also highlighted the challenges of observing the Arctic environment, and put in perspective CIMR capabilities compared with current instruments.

Plain Language Summary

The Copernicus Imaging Microwave Radiometer (CIMR) satellite instrument is currently being implemented to observe the Polar Regions. It will measure different variables, including the temperature and salinity of the ocean surface, and the sea ice extension in the polar ice caps. To help designing the instrument, a first instrument concept has been computer simulated. Together with simulations of the radiation emitted by the oceans, it allows to reproduce what the instrument antennas will measure. This is followed by further computations that apply mathematical algorithms to the simulated measurements to estimate the values of the ocean and ice parameters of interest. Studying these simulated measurements is then used to see whether the CIMR instrument concept is suitable to achieve the mission goals, and how much better CIMR will measure compared with existing instruments already observing similar variables. Although more work is required to keep refining the instrument and its computer simulations, this study shows that CIMR can achieve its mission goals, measuring more accurately and with better spatial resolution than previous instruments, and greatly contributing to monitor the rapid changes expected to take place in the Polar regions in the years to come.