Assessment of Spectra of the Atmospheric Infrared Ultraspectral Sounder on GF-5 and Validation of Water Vapor Retrieval

Atmospheric Infrared Ultraspectral Sounder (AIUS) aboard the Chinese GaoFen-5 satellite was launched on 9 May 2018. It is the first hyperspectral occultation spectrometer in China. The spectral quality assessment of AIUS measurements at the full and representative spectral bands was presented by comparing the transmittance spectra of measurements with that of simulations. AIUS measurements agree well with simulations. Statistics show that more than 73% of the transmittance differences are within +/- 0.05 and more than 91% of the transmittance differences are within +/- 0.1. The spectral windows for O-3, H2O, temperature, CO, CH4, and HCl were also analyzed. The comparison experiments indicate that AIUS data can provide reliable data for O-3, H2O, temperature, CO, CH4, and HCl detection and dynamic monitoring. The H2O profiles were then retrieved from AIUS measurements, and the precision, resolution, and accuracy of the H2O profiles are discussed. The estimated precision is less than 1.3 ppmv (21%) below 57 km and about 0.9-2.4 ppmv (20-31%) at 60-90 km. The vertical resolution of H2O profiles is better than 5 km below 32 km and about 5-8 km at 35-85 km. Comparisons with MLS Level 2 products indicate that the mean H2O profiles of AIUS have a good agreement with those of MLS. The relative differences are mostly within +/- 10% at 16-75 km and about 10-15% at 16-20 km in 60 degrees-80 degrees S. For 60 degrees-65 degrees S in December, the relative differences are within +/- 5% between 22 km and 80 km. The H2O profiles retrieved from AIUS measurements are credible for scientific research.