Like infrared radiation or microwaves, these waves usually travel in line of sight.
The Earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation is quite short, limiting their usefulness. In addition, producing and detecting coherent terahertz radiation was technically challenging until the 1990s. However, recent technologies using terahertz radiation have been developed, which are intended for applications such as medical imaging and surveillance.