THE DETERMINATION OF CLOUD PRESSURES FROM ROTATIONAL RAMAN-SCATTERING IN SATELLITE BACKSCATTER ULTRAVIOLET MEASUREMENTS

We have retrieved cloud pressures with the Nimbus 7 solar backscatter ultraviolet spectrometer and total ozone mapping spectrometer by utilizing properties of rotational Raman scattering. The retrieved cloud pressures are compared with coincident cloud pressures derived from the temperature humidity infrared sounder, as well as climatological cloud pressures from the International Satellite Cloud Climatology Project. Results show good agreement between cloud pressures measured using ultraviolet and infrared techniques, although a small bias is present. The bias in cloud pressures is likely due in part to different radiative properties of clouds at ultraviolet and infrared wavelengths. The ultraviolet measurements described here are sensitive to cloud optical thickness, while infrared measurements are sensitive to cloud top temperature. Ultraviolet cloud pressure measurements combined with measurements from other spectral regions may therefore provide information about cloud type. Cloud pressures measured by means of ultraviolet scattering properties will be more appropriate for use in satellite backscatter ultraviolet ozone retrieval algorithms. We suggest ways in which future ultraviolet remote sounding instruments may be designed to more optimally measure cloud pressure.