Half the year the polar regions are in darkness, making detection of icebergs using satellite observations with solar wavelengths useless. Objects on Earth are always emitting infrared energy, which can be used during the day or night. For this reason satellite radiometers measure infrared, or IR, energy. You can use the IR to track icebergs if the temperature contrast between the ice surface and the unfrozen waters provides good contrast. In this exercise, you will select an optimal IR wavelength to identify an iceberg. As with the solar exercise, there is more than one correct answer.