[MUSIC PLAYING] Christopher Hassall: The history of radar is relatively brief in technological terms, but its impact on the world has been substantial. On the 10th of July 1940, the German Luftwaffe launched a prolonged aerial assault on British shipping in the English Channel. Over time, these attacks wore down the British supply lines and threatened the island with starvation. German bombers regularly threatened London. However, the British had a secret weapon, radar. The radar could detect incoming German planes at a distance of 200 miles, that's 320 kilometers, and give the defending aircraft precise locations to intercept. The result was that the relatively small Royal Air Force was able to fight the Luftwaffe to a stalemate over a period of four months in what became known as the Battle of Britain. But where did this military radar come from and how does wartime air defence relates to counting insects in the sky? The history of radar goes back to Heinrich Hertz, a German physicist, who showed that radio waves (that's particular wavelengths of electromagnetic radiation) reflected off solid objects. We'll talk more about the physics of radar in the next part of the course. Another the German inventor, Christian Hülsmeyer, later submitted a patent for an early radar that could detect and measure the distance to ships in dense fog. However, Hülsmeyer's ideas were never taken up by the German military. After this, there are a series of developments around the world that became increasingly secretive through the 1930s as war loomed on the horizon. Perhaps, partly as a result of the secrecy, one of the key figures in radar history has been somewhat neglected. Robert Watson-Watt, a Scottish scientist and a relative of James Watt (the inventor of the steam engine), demonstrated the ability of radar to detect passing aircraft in 1935. By 1938, there was a secret network of 19 radars in the South of the UK that the German military didn't know about. It was this radar network that may well have won the Battle of Britain and turned the tide of the Second World War. However, the radars were detecting a lot more than just the enemy aircraft. Radar operators at the time had to be highly-skilled in distinguishing aircraft from the host of other objects in the air: rain and snow, smoke and ground clutter, and birds and insects that collectively made up the noise in the radar signal. Indeed, a scientific paper published in 1945 explains that the researchers had just been given permission to report that the army was able to spot individual seabirds flying over the surface of the sea as early as 1941. Following the war, radar technology proliferated and found many new uses. Marine radar was used for tracking ships, aviation radar helped to manage the boom in air travel and ground penetrating radar was used to understand the structure of the Earth without having to dig. However, for our purposes, we will focus on weather radar. After the war, surplus military radars were used to monitor the amount and location of precipitation. The value of the data that were generated led to the production of radars focused on detecting weather through the 1950s and into the 1980s. Soon, countries were constructing networks of weather surveillance radars to create national scale maps of weather. Those weather radars were put to good use, and have likely saved hundreds of thousands of lives over the years through early warning of extreme weather events, particularly the hurricanes that regularly strike the coastline around the Gulf of Mexico. Over the years, technological advances led to radars being able to differentiate many types of precipitation based on size, shape, and consistency. The result is that now Europe and North America have comprehensive weather radar networks, and networks are evolving rapidly elsewhere. But this does raise an important problem that is common across different fields of engineering: there is not equal access to this infrastructure, and therefore the benefits are not realised in terms of weather monitoring, or, in the future, the mapping of biodiversity. What do you think about the role of the military in driving the development of these technologies? Are there other examples that you are aware of where the government investment in the military has had secondary benefits? Please do go and share your thoughts in the discussion section at the end of this unit. In the next section of the course, we'll talk in more detail about the physics that underpins the sort of historical development that we've just discussed, and how the technology has evolved in important ways even since the start of the 21st century. [MUSIC PLAYING]
