Total Solar Irradiance (TSI), together with the absorption and reflection of this radiation by Earth's atmosphere, determines the global average temperature of Earth. Changes in both the solar irradiance and in the composition of the atmosphere can cause global climate change. Solar irradiance is purely a natural phenomenon, while the composition of the atmosphere is strongly influenced by the byproducts of modern industrial societies. Over the past century, the average surface temperature of Earth has increased by about 0.5 degree Celsius. Understanding whether the temperature increase and climate changes are byproducts of natural events or whether the changes are caused by man-made sources is of primary importance.

The continued measurement of Total Solar Irradiance to determine the Sun's effects on Earth's climate, at current state-of-the-art accuracy and without temporal gaps in the dataset, constitutes the solar irradiance requirement for the Glory mission. It is essential that there be no temporal gaps in the data, as any measured changes in the atmospheric temperature must be appropriately interpreted in the context of any changes in the solar irradiance.

TIM will collect high accuracy, high precision measurements of total solar irradiance using an active cavity radiometer that monitors changes in incident sunlight to Earth's atmosphere. Because TIM is designed to operate nominally in a solar-viewing orientation, it is mounted on a gimbaled platform that accommodates targeting independent of the spacecraft's nadir viewing attitude.

TIM is a heritage-design instrument that was originally flown on the SORCE satellite launched in January 2003.

TIM Data

The fundamental requirement for TIM is to make precise and accurate daily measurements of Total Solar Irradiance and connect them to previous TSI measurements to form the long-term climate record.

The continued measurement of the TSI to determine the Sun's direct and indirect effects on Earth's climate, at current state-of-the-art accuracy and without temporal gaps in the dataset, constitutes the solar irradiance requirement for the Glory mission and the objective of the Total Irradiance Monitor ( TIM ) instrument. It is essential that there be no temporal gaps in the multi-decadal measurement record of the TSI, as any measured changes in the atmospheric temperature must be appropriately interpreted in the context of any changes in the solar irradiance.

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