High Accuracy Climate Observations and Climate Forecast Testing

Benchmarking Radiance for Climate Change:

With the rapid increase in climate forcing through the addition of infrared active molecules to the atmosphere by fossil fuel combustion and the probability of carbon release from expanding melt zones in the Arctic, the need for irrefutable observations to define the current state of the atmosphere is becoming increasingly critical. The Zeus mission will provide a global benchmark climate record for this and future generations that, by virtue of its high accuracy determined against international standards on-orbit, establishes a new foundation for quantitatively defining the rate of climate change. Achieving this goal will provide decision support for a range of societal issues including water resources, human health, natural resources, energy management, insurance infrastructure, and others that are linked to our understanding of how climate is changing. The first science objective of Zeus is to provide a benchmark of the thermal infrared radiance spectrum against which similar future observations can be compared to establish atmospheric change with credibility.

Benchmarking Radiance for Climate Forecast Testing:

Significant uncertainties exist in forecasts of our future climate. For example, the differences between the IPCC Fourth Assessment models are significant indeed, ranging from virtually no predicted change to a change of 0.6 K/decade between the Japanese medium resolution model and the GISS-EH model for the North American region respectively. Central to the climate sensitivity discrepancy among different IPCC models is their different climate feedback strengths. To narrow down the uncertainty of climate projection given by the ensemble of these models, it is imperative to measure and confront these models with the feedback strengths measured from observations. To address this issue, the second science objective of Zeus is to provide a benchmark of the thermal infrared radiance spectrum to determine longwave forcings and longwave feedbacks for testing climate models.

Benchmarking Radiance for Reanalysis and Intercalibration:

Weather forecast systems utilize data from a wide range of satellite systems and sensors that are primarily designed for operational weather forecast requirements. Eliminating biases among the various sensors is important for making optimal use of the data, and is a primary goal of the Global Spacebased Intercalibration System (GSICS) and data assimilation centers. A spectral radiance dataset with high accuracy and on-orbit traceability is required for both Reanalysis methods employing data assimilation techniques and direct intercalibration techniques such as Simultaneous Nadir Overpass (SNO) analyses to anchor the calibration of the operational weather sensors. Addressing this issue, the third science objective of Zeus is to provide a benchmark of the thermal infrared spectrum that can provide reference intercalibration for other sensors and for anchoring reanalysis.