WPenner's Blog

SpaceQ recently teased readers with an article titled Earth Observation Satellite Market About to Boom. Though behind a paywall, the gist of the article, to everyone paying attention to the satellite sector, is clear: Earth observation is hot and getting hotter. In a previous article, I examined the newest technology, hyperspectral imaging, to understand how it works. Understanding the role radio frequencies play in earth observation is also crucial. Having never considered it before, I did not realize how fascinating it is.

Radio frequencies (RF) are a category of electromagnetic radiation, which includes visible light, ultraviolet radiation, and x-rays. ¹ This makes it similar to a hyperspectral sensor, which takes light waves and breaks them apart by running them through a prism. ²

The RF band spans the section of the electromagnetic spectrum between 3kHz - 300GHz and travel at the speed of light. Hertz is a measurement seen all the time on computer boxes, but not everyone has a clear mental picture of what that means. 1Hz = 1 wave per second as measured either from peak to peak or trough to trough. So, 3 kHz = 3,000 waves per second and 300GHz = 300,000,000,000 waves per second.

Different radio frequencies interact with atmospheric conditions uniquely. They are reflected, absorbed, scattered, refracted and diffracted differently depending on the frequency and the condition. This property allows operators to differentiate signals to detect tornados, hurricanes, humidity, cloud types and coverage, wind speeds and direction, precipitation types and amounts. The ability to detect these phenomena makes radio frequencies a mainstay for weather forecasting.

Radio waves can also detect physical properties of the earth, such as wave heights, storm surge, ocean currents, and other conditions. ¹ Hyperspectral images may replace radio frequencies in detecting physical earth properties, but probably not atmospheric ones. While some radio waves are great for their ability to pass through interference, making them inappropriate for atmospheric observation, obscuring obstacles easily block visible light.³