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Question: "The temperatures do not appear to be realistic. What does this AMSU-A temperature image show?" Answer: The AMSU measures very low levels of microwave radiation naturally emitted by the Earth at different frequencies (or "channels"). The land, ocean, and atmosphere all have different emitting properties at different microwave frequencies. The amount of radiation measured by each AMSU channel is converted to a "brightness temperature". The brightness temperature of a substance is its real temperature multiplied by the substance's ability to emit radiation (its "emissivity"). For the AMSU frequencies, the emissivities range from about 0.4 (snow cover) to 0.5 (ocean) to 0.95 (dry land or vegetated land) to 1.0 for air. Each channel has a different mixture of sensitivities to these various features. More Info NASA Contact: Michael Goodman |