Tradeoffs in Hyperspectral Infrared Observations from Space for Weather and Climate

Observation of the upwelling radiance spectrum of the Earth from space in the infrared has demonstrated considerable value to scientists and operational agencies for prediction of weather and climate change. Scientists using data from the Atmospheric Infrared Sounder (AIRS) on Aqua have demonstrated between 6 and 11 hours improvement on the 6 day forecast. AIRS water vapor and temperature profiles have identified biases in climate models and have quantified the level of positive feedback of water vapor with global atmospheric warming. AIRS radiances have been used to quantify the global distribution of CO2 in the mid troposphere. Hyperspectral infrared radiances from other spaceborne instruments including the NASA Tropospheric Emission Spectrometer (TES), and the European Infrared Atmospheric Sounding Interferometer (IASI) have found similar results.

While AIRS and the other infrared sounders have proven quite valuable for science investigations, as weather and climate models advance in both spatial (horizontal), spectral, and temporal resolution (including diurnal cycle), we find that even these systems have deficiencies. For example horizontal resolution of weather forecast models were originally in the 100's km scale are now operating in the 10's of km and are expected to be in the few km scale before too long. Scientists wishing to see the evolution of cloud formations in the boundary layer and the interaction with water vapor would like more visits throughout the day. In some cases, for example the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission in NASA Decadal Survey requires only annual zonal means for long-term stability detection.

We examine the tradeoff of horizontal resolution and temporal revisit on instrument size vs orbit, and present a concept for a 1km version of AIRS , called ARIES. We also examine the tradeoff of multiple satellites (i.e. constellation), and demonstrate continuous real-time observation on a global scale for the Medium Earth Orbit configuration. We also match the various requirements for near real time global and regional forecasting and climate processes vs climate trends with the observational scenarios considered. We examine tradeoffs in how these systems should be phased in to operational use based on on technical risk and scientific payoff.