Single frequency refers to a research area in which measurements, signals, or data are restricted to a single frequency or wavelength. This approach is often used in various fields such as signal processing, communications, and remote sensing to simplify the data analysis and processing. Single frequency techniques can provide higher precision and accuracy in certain applications where the information of interest is concentrated at a specific frequency. Research in this area often focuses on developing algorithms, methods, and technologies for extracting, analyzing, and interpreting data based on a single frequency.