Impact of Variable Channel Bandwidths on Microwave Hyperspectral Retrieval of Atmospheric Temperature and Humidity Profiles

Microwave hyperspectral sounders are key instruments for next-generation meteorological satellites, designed to replace broadband sounders such as ATMS, MWTS, and MWHS. A major challenge in their design is determining the optimal channel bandwidth configuration to maximize the use of absorption spectra and enhance vertical atmospheric profiling. This study evaluates two variable-bandwidth strategies: (1) a generalized variable-bandwidth approach, which applies multiple fixed bandwidth combinations across different frequency bands, and (2) a dynamic bandwidth strategy, which differentiates channel bandwidths within the same frequency band for absorption peak and wing regions. The retrieval performance of various bandwidth configurations is analyzed for lower- and upper-atmospheric temperature and humidity observations. Results indicate that for upper-atmosphere temperature retrievals, the 60 GHz and 118 GHz bands achieve higher accuracy with a 10 MHz bandwidth. For lower-atmosphere temperature retrievals, where most information originates from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line’s wing region, a wider bandwidth reduces observation costs while maintaining comparable accuracy. Water vapor retrievals, which primarily rely on the 118 GHz wing region and 183 GHz absorption lines, show minimal sensitivity to bandwidth configurations. A novel channel configuration method is proposed, integrating both absorption peak and wing regions into a single optimized scheme. Experimental results demonstrate that the 10+10+100 MHz (Peak) + 50+100+100 MHz (Wing) configuration achieves the best retrieval accuracy across different atmospheric layers, significantly improving both temperature and humidity profiling compared to existing broadband sounders. The advantages of using variable channel bandwidth hyperspectral microwave radiometers for joint retrieval of temperature and humidity profiles have been demonstrated from both theoretical analysis and quantitative retrieval (Optimal estimation method, OEM), providing theoretical support and technical guidance for the development of the next generation of spaceborne hyperspectral microwave radiometers.