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As a secondary goal, GRACE will provide critical information about the Earth's atmosphere. Each day the GRACE mission will provide several hundred measurements of how the signals from Global Positioning Satellites (GPS) are affected as they travel through the atmosphere. Just as light is refracted or bends as it enters water, the GPS signals arerefracted as they pass through the atmosphere. By observing the signals in the atmosphere, profiles of the pressure, temperature, and humidity can be derived. These clues help the scientist predict the weather around the Earth. The GPS receivers on the GRACE satellite track refracted signals from the GPS satellites as they rise or set through the Earth's atmosphere. The scientific term for this measurement is known as occultation and will be measured throughout the mission life to assist us in predicting global weather.