  We are using computer models to explore the observational sensitivity to
changes in atmospheric and surface properties, and the detectability of
biosignatures, in the globally averaged spectra and light-curves of the Earth.
Using AIRS (Atmospheric Infrared Sounder) data, as input for atmospheric and
surface properties, we have generated spatially resolved high-resolution
synthetic spectra using the SMART radiative transfer model, for a variety of
conditions, from the UV to the far-IR (beyond the range of current Earth-based
satellite data). We have then averaged over the visible disk for a number of
different viewing geometries to quantify the sensitivity to surface types and
atmospheric features as a function of viewing geometry, and spatial and
spectral resolution.
  These results have been processed with an instrument simulator to improve our
understanding of the detectable characteristics of Earth-like planets as viewed
by the first generation extrasolar terrestrial planet detection and
characterization missions (Terrestrial Planet Finder/Darwin and Life finder).
The wavelength range of our results are modelled over are applicable to both
the proposed visible coronograph and mid-infrared interferometer TPF
architectures.
  We have validated this model against disk-averaged observations by the Mars
Global Surveyor Thermal Emission Spectrometer (MGS TES).
  This model was also used to analyze Earth-shine data for detectability of
planetary characteristics and biosignatures in disk-averaged spectra.
