Abstract: The National Natural Science Foundation of China has actively pursued reform work, with “optimizing the layout of disciplines” as one of the primary tasks, and the adjustment of discipline application codes is an important component and entry point of this task. This work is being done in order to adapt to the new round of scientific and technological development. From 2019 to 2022, the Department of Atmospheric Sciences of the National Natural Science Foundation of China reformed the secondary application codes. D0509, “Atmospheric observation, remote sensing, and detection technologies and methods,” incorporated all atmospheric observation research. The D0509 is defined as “supporting technologies” to differentiate it from “sub-disciplines” and “development areas” of science. At present, D0509 has designed six research avenues from two perspectives, based on the basic level of the discipline and the specific application level, with approximately 20 keywords for each direction. This article describes the reforming process of the D0509 code and interprets the research directions and keywords from the perspectives of the importance, connotation, extension, and development trend of atmospheric observation, remote sensing, and detection technologies and methods. It helps applicants and review experts accurately select keywords according to their academic backgrounds and facilitates the accurate matching of proper reviewers to each proposal.