Where am I? Photonics answers Captain James Cook

Since the dawn of time men have been wondering what was hiding behind the horizon, above the clouds and under the oceans. This fascination triggered the first migrations, the bloodiest conquests and ultimately, the advance of humankind on the entire planet Earth, including its most remote and unwelcoming lands from equator to the ices of Antarctica.

During the 3rd Century BC Eratosthenes set the cornerstone of modern navigation by measuring the size and shape of the Earth: he paved the way for georeferenced data but, while the math was getting better, the tools were still missed for centuries.

Finding the current local time based on the sun or stars was easy enough on firm ground but at sea, until someone could build a clock that could resist the rocking of the waves and the corrosive effect of salt spray over a lengthy sea voyage, it was impossible to keep track of the time back home while traveling. So, if sailors clearly understood that ? live ? latitude and longitude were the most accurate way to sail, they were desperately missing the tools to do it until an English carpenter named John Harrison invented in 1764 a device called a chronometer.

In 1779, during the globe circumnavigation, James Cook used Harrison’s chronometer crosschecking it with constant astronomical observation and data on ship coarse from compass and measured speed: when he returned, his calculations of longitude proved correct to within 8 miles (13 km) versus a quite common and serious navigational error of 60 miles. From information he gathered on his voyage, Cook completed many detailed charts of the world that completely changed the nature of navigation because he can place himself on the surface of the globe, with exactly measured latitude and longitude. James Cook set a method and, as the decades progressed, more people were trained while better instruments became available.

In the twentieth-century the advent of, first, radio signals and, later, satellites positioning systems made that method obsolete:  electronic receivers can determine their location using longitude, latitude and elevation, via time signals transmitted along a line of sight, from satellites. The term GPS (Global Position System) became part of our everyday language to talk about satellite navigation even if it refers to the system made by US while  Russia, China and recently Europe have their own satellites.

By the way satnav is essentially a step back from Cook’s method because it is based on artificial marks placed in the space: at the end, even on different scale, it is again a coastal navigation based on visible landmarks. Moreover, the intrinsic dependency from radio communications as well the potential vulnerability from hostile hacking of the satellite network represent the most critical points.  

Photonics technologies are changing again the game or, better, is leading back to Cook’s method: a precise evaluation of the coarse or, in other words, exact measurements of  direction and time is nowadays feasible thanking to light. A integrated system based on ring laser gyroscopes and atomic clocks (based on laser-cooled atoms) provide nowadays these data with an unsurpassed precision. Moreover such system can be installed on-board and it is inherently independent from any external references.

Captain John Cook, ?thanking to Photonics, now we know “where we are”!