Comparative experimental validation of microwave hyperspectral atmospheric soundings in clear-sky conditions

Abstract. Accurate observations of atmospheric temperature and water vapor profiles are essential for weather forecasting and climate change detection. Hyperspectral radiance measurements afford a useful means to retrieve these thermodynamic variable fields, by harnessing the rich information contained in the electromagnetic wave spectrum of the atmospheric radiation. Compared to infrared radiometry, microwave radiometry holds the ability to penetrate clouds and potentially achieve an all-sky thermodynamic retrieval. Recent technological advancements have enabled the development of a hyperspectral microwave radiometer, the High Spectral Resolution Airborne Microwave Sounder (HiSRAMS), which we employ in this study to retrieve the atmospheric temperature and water vapor profiles under the clear-sky condition, in comparison with an infrared hyperspectrometer, the Atmospheric Emitted Radiance Interferometer (AERI). HiSRAMS and AERI measurements under different viewing geometries have been acquired and compared for atmospheric retrieval. When both instruments are placed on the ground to acquire zenith-pointing measurements, the infrared hyperspectral measurements exhibit higher information content and greater vertical resolution for temperature and water vapor retrievals than the microwave hyperspectral measurements. A synergistic fusion of HiSRAMS and AERI measurements from the air and ground, respectively, is tested. This “sandwich” sounding of the atmosphere takes advantage of the complementary information contents of the two instruments and is found to notably improve retrieval accuracy.