The thermal infrared radiances measured by NISTAR will provide broadband observations that can serve as a global index of the Earth's climate. The data can be interpreted in terms of the effective emitting temperature of the planet and thus, NISTAR can act as a kind of global thermometer. The observed seasonal and interannual variability could be compared with simulated signals from climate models to assess the significance of any observed short or long-term fluctuations.
When combined with the EPIC imagery and retrievals of cloud properties, the NISTAR shortwave radiances will produce estimates of the global albedo. The derived albedo values, or the original radiance data, can serve to evaluate the radiation calculations in GCMs. The NISTAR shortwave and longwave radiances will also be used to estimate errors in the albedos and longwave fluxes derived from interpolations of sparsely sampled LEO data, the more conventional technique for measuring the Earth radiation balance. The NISTAR spectral complement will also provide new data to confirm or negate previous estimates of the ratio of near-infrared (NIR) to visible (VIS) albedos. The NIR/VIS ratios have been used extensively to quantify differences between measured and modeled cloud radiative properties. It will provide a globally integrated test of the episodic but highly time- and space-localized findings of discrepant NIR/VIS cloud albedo ratios (Stephens and Tsay, 1990; Francis et al., 1997; Valero et al., 1997, 1999).
Because the near-infrared channel is sensitive to vegetation and snow/ice cover in addition to clouds, the NIR/VIS ratio is an attractively simple and fundamental analysis tool for studying global change, and Triana is the perfect vantage point to begin using that tool. (No current or planned LEO or GEO Earth radiation budget satellites have a broadband near-infrared channel, although CERES is apparently planning to add one in the post-2003 timeframe, which should serve as a nice complement to that on Triana.)
A modeling infrastructure will be developed based upon existing efforts at NCAR, participating NASA laboratories, and other institutions. This modeling infrastructure will be used to simulate the NISTAR signals and EPIC spectral imagery. Because of Triana¹s simple viewing geometry and relatively simple data processing requirements compared to LEO satellites, scientists and students would be able to study a wide variety of phenomena without many of the complexities usually associated with remote sensing. Because of the lunar calibration for EPIC and absolute calibration for NISTAR, the scientific community would be able to focus on geophysical applications of a stable, high-accurate data set. This could have important repercussions both for remote sensing and climate.