Sea Surface Temperature (SST) is a crucial parameter for operational Arctic weather and met ocean forecasts. It can be measured from Space using two types of satellite instruments:

• InfraRed (IR) radiometers, such as SLSTR on board the Sentinel-3 satellite have fine spatial resolution and excellent accuracy. They can however not see through clouds.
• Passive Microwave radiometers, such as CIMR have coarser spatial resolution and are not as accurate. They can however see through clouds and measure SST and sea-ice cover in the polar regions.

The example below show how CIMR (right) fills the many gaps due to cloud cover from the "pure IR" (left). Monitoring all-weather polar SST is key for the operational monitoring and forecasting by the Copernicus Marine Environment Monitoring Service (CMEMS), and is one of the two primary objectives of the CIMR mission (the other primary objective is pan-arctic daily sea-ice concentration with a spatial resolution better than 5km).

Two Sea Surface Temperature (SST) maps, left with only InfraRed (IR) satellites (e.g. Sentinel-3 SLSTR), and right adding a Passive Microwave instrument such as CIMR. Grey area over the ocean denote missing data, mainly due to cloud cover (left). This example is for summer 2012, when sea ice retreated at a record low extent.

[Credit: Jacob Høyer, CMEMS/DMI].