Saastamoinen's Law is a principle in atmospheric science that describes how the refractive index of the atmosphere changes with altitude. It specifically relates to the bending of radio waves as they travel through different layers of the atmosphere. This bending can affect the accuracy of radio communication and navigation systems. The law is named after J. Saastamoinen, a Finnish scientist who contributed to the understanding of atmospheric effects on radio signals. By applying this law, engineers and meteorologists can better predict signal behavior, improving the reliability of various technologies that rely on radio wave transmission.