A method is presented for treating the transport of resonance radiation under the influence of a varying Doppler width resulting from temperature changes. The method is applied to transport of resonance photons in the earth's thermosphere for media of modest and large optical depths. The drop in temperature below the exosphere can lead to almost a factor of two reduction in the nadir viewing intensity observed, e.g., from satellites. The effect is weaker, however, for zenith viewing intensities, especially in the isothermal region.