Jupiter and Saturn from 2 to 6 microns

Earth based spectroscopic observations that support current compositional and structural analyses of planetary atmospheres are summarized. The overview of Jupiter's IR spectrum illustrates a fundamental constraint to observations of the outer planets: atmospheric studies are restricted to narrow, isolated windows defined by the planetary absorbers H2, CH4, NH3, and PH3. Some of these planetary windows, such as at 1.6 micron are accessible in ground based observations, but others, such as at 1.9 and 2.7 micron are totally obscured by terrestrial H2O. For this reason, high altitude sites, such as aircraft, balloons, and spacecraft, are essential for IR spectral studies of the outer planets.