Abstract Nimbus 4 IRIS spectra (2.8 cm−1 spectral resolution) exhibit a number of narrow window regions in the 700–1300 cm−1 region suitable for estimating surface temperature from infrared remote sounding measurements. Degraded to 10 cm−1 resolution, the spectra indicate windows near 936 and 960 cm−1 which are significantly more transparent than the 899 cm−1 window presently used in operational remote sensing systems.