Note the "coldness" of clear and calm ocean surfaces that results from low emissivity values. Since ocean emissivities are lowest at the lower frequencies and land emissivities highest, land ocean separation is most effective at the lower frequencies. Also note how the introduction of sea ice, clouds, and precipitation acts to significantly increase brightness temperatures at the lower frequencies. The increase from clouds and precipitation is due to the addition of emitted energy, while sea ice has a higher emissivity than open water. For the case of heavy convective precipitation, note how scattering by ice causes brightness temperatures to become lower than those for a clear calm ocean surface.