Using radio waves to study planetary atmospheres

In the field of electrical engineering, complex coding and signal processing techniques are the norm. Thus, it is refreshing to consider the amount of planetary science that can be done simply by using a high-quality radio. The radio, usually located on an exploring spacecraft, transmits a simple, single-frequency, sinusoidal tone that sweeps through a planet's atmosphere. After the electromagnetic energy passes through the atmosphere, it is received on the other side of the planet. Then, researchers analyze and detect the changes in the received signal energy caused by the interaction with the planet's atmosphere. The information from the received signal is used to determine the number density of particles, the temperature, and the pressure of the volume of atmosphere that the signal passed through. This method of remote sensing is known as radio occultation. The technique was first used in the summer of 1965 to measure the surface pressure on Mars. Since then, the atmospheres of all of the planets in the solar system (except for Pluto), and of some satellites, have been studied just by using a simple, sinusoidal radio signal. With continued application of the radio occultation method and with the development and implementation of higher-output multiple spacecraft constellations, the future promises to be even more productive.