The History of Radar: Demystifying Satellite-Based Leak Detection

Radar is a vital tool in this rapidly changing world. It has been used various in sectors such as the military to scientific research. Using radar, we can detect things such as aircraft, ships, spacecraft, guided missiles, ancient ruins under forests, the impact of weather events, and changes to the terrain.

How Was Radar Discovered?

In order to answer this question, we need to revisit 1880’s Germany to find the young Professor Heinrich Hertz on the verge of making a discovery: all in an effort to confirm if James Clerk Maxwell’s 1864 theory of Electromagnetism was correct. But what does this theory mean?

Maxwell published, “A Dynamical Theory of the Electromagnetic Field,” in 1865, where he demonstrated that electric and magnetic fields travel through space as waves move at the speed of light. “He proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena” [1].

Due to Maxwell’s equations for electromagnetism, his work has been called the “second great unification in physics,” after the first one realized by Isaac Newton [2]. But it is important to remember this was all theory and mathematical equations until Hertz came along in the 1880s.

So, what part did Hertz play?

Hertz was curious to test Maxwell’s theory, and during his tenure at Karlsruhe Polytechnic, Hertz became the first person to send and receive radio waves. He was able to show that the nature of the wave’s reflection and refraction was similar to the nature of light, which confirmed that light waves are in fact electromagnetic radiation and conformed to the laws of Maxwell’s equations [3]. During an experiment to test the movement of electricity, in which Hertz used sparks emitted across a gap in a short metal loop attached to an induction coil, he discovered that by measuring the side sparks that formed around the primary spark and varying the position of the detector, the signal exhibited a wave-like pattern.

This discovery lead to the development and understanding of “wavelengths” and their use in the communications realm.

The First Transmitter-Receiver System: The Next Step Toward Radar

The next stop on our historical voyage takes a jump of twenty years to 1904 when Christian Huelsmeyer applied for a German patent for his “telemobiloscope,” a device that was used as a transmitter-receiver system meant to detect distant metallic objects by means of electrical waves. A copy of the drawn image from Huelsmeyer’s US Patent 810,150 dated Jan. 16, 1906 is shown in Fig. 1.

Figure 1: Christian Huelsmeyer’s US Patent 810,150 – Jan. 16, 1906

This transmitter-receiver system was originally designed to prevent ship collisions in the water and could detect other vessels up to 3,000 m away. However, even though the tests proved positive and the public opinion of the technology was favorable, the military and private industry did not show interest in the capabilities of his device.

Pulse Radar: Radar Begins as We Know It

In 1934, a new scientist came on the scene by the name of Robert Morris Page.  After his graduation from university, he joined the U.S. Naval Research Laboratory (NRL) where he began development on a low-priority project, “pulse radar.” The U.S. Navy had no use for such a device, but within a few short years, it was successfully installed and demonstrated at sea. By the time the U.S. entered World War II, 79 radars were installed onto various ships in the U.S. Navy. These radars are credited with giving the U.S. an advantage over Japan in the Pacific Theater.

Radar: Radio Detection and Ranging

When World War II began, there was a race to develop technology faster than the enemy. In the 1930’s, several countries were making these developments as the war ravaged their homes. Prompted by rumors that the Germans were possibly developing a “death ray,” the Air Ministry of England commissioned Sir Robert Watson-Watt to see if this ray was truly possible. After some experiments, Watson-Watts concluded that a death ray was unlikely but turned his attention to “…the difficult, but less unpromising, problem of radio-detection as opposed to radio-destruction,” [4].

In February of 1935, Watson-Watts demonstrated to the Air Ministry the first practical radio system used for detecting aircraft. Within a few short years, Watson-Watts had a patent and was using pulsed radio waves to detect planes up to 80 miles away!

This technological innovation helped to turn the tide of the war, thus bringing victory to the allies. The military dubbed the invention “RADAR,” or Radio Detection and Ranging.

Synthetic Aperture Radar (SAR): The Start of Something New

Synthetic Aperture Radar (SAR) was developed in the 1950s as a surveillance tool. The need for this tool came in the 1940s to have an all-weather, 24-hour aerial remote surveillance device. The problems with aerial imagery at the time dealt with issues such as cloud cover, where the clouds were lower than the plane when the image was taken, or limited hours of daylight. The military needed to be able to see through clouds and extract data in the dead of night.

Due to radar’s ability to penetrate clouds and fog, and its non-dependence on the wavelengths of light since it used its own wavelengths, it became the logical choice for the innovation. This airborne imagery made it possible to see the surface in a way that had never been done before.

SeaSat: The Ultimate Discovery of Satellite SAR

The SeaSat satellite was developed at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, CA, with a SAR sensor on-board with the purpose of studying the ocean. During its brief 110-day mission, it collected more data than 100 years of oceanic data collected from ships combined. This was mind-blowing at the time and opened the door to a new realm of data collection.

For a more in-depth discussion of SeaSat and its mission, read more here.

SeaSat was the first satellite of its kind: launched in 1978, it carried the first ever civilian spaceborne imaging radar instrument (the SAR instrument), and even after its untimely demise at the hands of a malfunction, it spawned many subsequent Earth remote-sensing satellites and instruments that track changes in Earth’s oceans, land, and ice. These advances were eventually applied to missions to other planets, and subsequently, lead to the discovery of Utilis’ technology!

I hope you had some fun demystifying the history of radar. Tune in next time for part 2 of the Utilis blog learning series.

Until Next Time!

~Kati B.

Citations

[1] Maxwell, James Clerk (1865). “A dynamical theory of the electromagnetic field” (PDF). Philosophical Transactions of the Royal Society of London. 155: 459–512. Bibcode:1865RSPT..155..459C. doi:10.1098/rstl.1865.0008. Archived (PDF) from the original on 28 July 2011. (This article accompanied an 8 December 1864 presentation by Maxwell to the Royal Society. His statement that “light and magnetism are affections of the same substance” is on page 499.)

[2] Nahin, P.J. (1992). “Maxwell’s grand unification”. IEEE Spectrum. 29 (3): 45. doi:10.1109/6.123329.

[3] Spark Museum. “The Discovery of Radio Waves – 1888 Heinrich Rudolf Hertz (1857-1894).” Spark Museum of Electrical Invention, Spark Museum of Early Radio and Scientific Apparatus, 2019, www.sparkmuseum.com/BOOK_HERTZ.HTM.

[4] Kramer, Herbert J. “SeaSat Mission — the World’s First Satellite Mission Dedicated to Oceanography.” SeaSat – EoPortal Directory – Satellite Missions, EoPortal Directory, 2002, directory.eoportal.org/web/eoportal/satellite-missions/s/seasat.