As seen in Figure 2.03, because the ocean, land, atmosphere, and clouds have relatively similar temperatures, all of these sources emit microwave energy. Earth also receives microwave radiation from the Sun, other galactic bodies (stars), and "empty space." (Although "empty space" is very cold, ~4 K, it does have a temperature and emits energy in the microwave portion of the electromagnetic spectrum.) Therefore, a satellite sensor measuring electromagnetic energy at microwave wavelengths will actually receive this energy from
Were interested in inferring sea ice concentration from measurements of the surface emissions of microwave electromagnetic energy. The goal here, then, is to either minimize or correct for the energy arriving at the satellite from the other sources. We'll look first at how to minimize the influence of the atmospheric emissions.