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A New Low Frequency Microwave Radiometer for an All-Weather, High Spatial Resolution, and Accurate Estimation of Ocean and Sea-Ice Parameters
[29-Aug-2018] Kilic, L., Prigent, C., Aires, F., Boutin, J., Heygster, G., and Meissner, T.
Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing Meeting
Surface characterization from satellites is required to understand, monitor and predict the general circulation of the ocean and atmosphere, the interaction between the surface and the atmosphere, as well as the water and energy cycles. With more than 70% cloud coverage at any time, visible and infrared satellite observations only provide limited information. Regardless of the cloud cover, passive microwaves offer ocean and sea ice information such as Sea Surface Temperature (SST), Ocean Wind Speed (OWS) even under extreme conditions, Sea Surface Salinity (SSS), Sea Ice Concentration (SIC) or thin Sea Ice Thickness (SIT). These products are particularly important for polar regions that are very vulnerable to climate change. Up to now all these oceanic/sea ice parameters estimated from passive microwave observations are limited in spatial resolution and/or accuracy.
We propose to present an innovative low-frequency passive microwave mission explored within the Copernicus program: the Copernicus Imager Microwave Radiometer (CIMR). It will observe at 1.4, 6.9, 10.65 and 18.7 GHz (L, C, X and Ku bands) and possibly at 36 GHz (Ka band), in a polar orbit with low-noise fully polarized receivers, and a foldable mesh antenna of 7 m- diameter. It is expected to fly in tandem with MetOp-SG B to cover the full microwave spectrum from 1.4 GHz to 664 GHz for the first time.
Thanks to simultaneous measurements between 1.4 and 18.7 GHz (L, C, X, and Ku bands), CIMR combines the merits of the AMSR and the SMOS/SMAP/Aquarius type missions. It will provide global, simultaneous and consistent retrievals of SST, SSS and SIC, twice daily and regardless of the cloud cover. CIMR will estimate SST with a precision of 0.2 K and a spatial resolution of 12 km. It will estimate SSS with an instantaneous precision of better than 0.3 psu, and a spatial resolution of 52 km. Accurate measurements of SST and SSS will be provided up to 20 km to the coast and transition zones. The SIC will be retrieved with a precision of 5% and 12 km spatial resolution. A 36 GHz channel could be added to provide a better spatial resolution to the SIC retrieval in addition to help constrain the liquid water contribution to the signal.
For instance, with the SST and SSS controlling the density of the sea water, twice daily accurate instantaneous estimate of SST and SSS will lead to an improved understanding of the thermohaline circulation. By the same token, the consistency between high resolution SST and SIC measurements will also be a significant step forward for all applications addressing ocean/sea ice interactions in the marginal ice zone, with rigorous collocation and identical spatial/temporal sampling of the products, as compared to a multi-platform approach.
With no guarantee of successors to AMSR2, SMOS and SMAP, the CIMR mission will provide continuity in the observations of low frequency microwave measurements, with much improved spatial and radiometric characteristics, for an all weather observations capability of key ocean and sea-ice surface parameters. This new concept is, therefore, a serious candidate for a future Copernicus mission.

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