Nistar has been collecting earth out-going irradiance from the sun-LIT earth in 4 bands for the past 33 months while orbiting L1

Collectively the bands provide measurement of the total long wave and short wave reflected and emitted radiation from the earth at a limited range of solar angles. These measurements assist in answering questions of the earths radiation imbalance and future climate change. The uncertainty goals of less-than 1.5 percent for nistar are very challenging and they require a great deal of attention to both the ground calibration and determination of the on-orbit degradation of the instrument. This challenge has been complicated by differences in the thermal environment during ground testing compared to that during operation in-space. The primary difference is that in space the thermal background contributes much more to the signal of interest than IT did during laboratory testing. The issue makes IT difficult to properly tune the instrument time response on-orbit which is necessary for accurate use of the ground calibration. So far efforts to tune the instrument appear to be successful however the degree of success has been difficult to quantify precisely. A comparison between the nistar short-wave data and synthetic data derived from other earth viewing sensors reveals a disagreement of approximately 15 percent. To further investigate this discrepancy we propose a RE-analysis of the on-orbit nistar instrument response to better quantify potential calibration errors. The analysis does not rely on other earth observation data just that collected by nistar. From this effort corrections and uncertainties will be derived and applied to nistar data which requires changes to future data processing and reprocessing of existing data.