{"id":59746,"date":"2017-08-16T11:22:16","date_gmt":"2017-08-16T15:22:16","guid":{"rendered":"http:\/\/www.bu.edu\/eng\/?p=59746"},"modified":"2024-03-13T16:19:19","modified_gmt":"2024-03-13T20:19:19","slug":"solar-eclipse-scientific-opportunity","status":"publish","type":"post","link":"https:\/\/www.bu.edu\/eng\/2017\/08\/16\/solar-eclipse-scientific-opportunity\/","title":{"rendered":"Solar Eclipse, Scientific Opportunity"},"content":{"rendered":"

Engineering team will measure effects on GPS; ultimate goal is citizen science<\/h2>\n

By Catherine Caruso, BU Research<\/em><\/p>\n

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During the solar eclipse on August 21, the moon will completely block the sun\u2019s energy from reaching Earth within a 70-mile shadow that will sweep across the US, presenting scientists with a unique research opportunity. Photo courtesy of NASA<\/p>\n<\/div>\n<\/header>\n

On August 21, 2017, the US will play host to a rare natural phenomenon: a complete\u00a0<\/span>solar eclipse<\/a>\u00a0that will cut a swath from Oregon to South Carolina. And as people across the country clamor outside, eclipse glasses in hand, to see the remarkable sight of the moon blocking the sun,\u00a0<\/span>Joshua Semeter<\/a>\u00a0<\/span>and his research team will be busy using GPS sensors to gather data on the Earth\u2019s upper atmosphere.<\/p>\n

Semeter, a Boston University College of Engineering professor of\u00a0<\/span>electrical and computer engineering<\/a>, and his team will scatter inexpensive GPS sensors in the path of the eclipse to take measurements as it moves overhead. If all goes as planned, the project will not only deepen our understanding of Earth\u2019s upper atmosphere\u2014which has the potential to disrupt technology like GPS navigation systems\u2014but will also demonstrate how cheap GPS sensors like the ones in smartphones could be used for broader \u201ccitizen science\u201d initiatives.<\/p>\n

During a total solar eclipse, the moon is perfectly aligned between the Earth and the sun, blocking the sun\u2019s energy from reaching the Earth within a large shadow that moves across the Earth\u2019s surface. On August 21, this eclipse shadow, which Semeter calls a \u201csupersonic sun shade,\u201d will be 70 miles across and sweep across the US at between 1,500 and 3,000 miles per hour, taking about 90 minutes to travel from coast to coast. People directly under the eclipse path will have the eerie experience of watching the sun seemingly disappear during broad daylight, while those further from the path will see the sun partially covered.<\/p>\n

But this total solar eclipse is more than a rare natural phenomenon: for scientists, it is a unique research opportunity. \u201cIt\u2019s like a controlled experiment,\u201d Semeter explains. \u201cMother Nature is providing us a nice experimental environment.\u201d<\/p>\n

Semeter studies the\u00a0<\/span>ionosphere<\/a>, a layer of charged particles (electrons and ions) between 30 and 600 miles above the Earth\u2019s surface. The ionosphere is formed when ultraviolet radiation from the sun hits the Earth\u2019s upper atmosphere, knocking electrons free from their parent atoms. This layer is a tricky challenge for GPS navigation systems: it slows down and bends radio waves passing through it, forcing GPS devices to correct for it. The size of the correction depends on the density of charged particles, or plasma, that the radio waves travel through on their way from satellite to GPS receiver.<\/p>\n

Semeter\u2019s team, helmed by PhD student\u00a0<\/span>Sebastijan Mrak<\/a>\u00a0<\/span>(ENG\u201921), wants to know what happens to the ionosphere as the eclipse shadow, which is totally devoid of the sun\u2019s ultraviolet radiation, plows across the country. To figure it out, the researchers will head to Missouri\u2014on the path of the eclipse\u2014and deploy 20 cheap GPS receivers at schools and homes alongside much fancier GPS receivers already installed throughout the state. (The Missouri Department of Transportation received a block grant several years ago to install sensors throughout the state, and Missouri now has one of the best networks of high-quality GPS sensors anywhere in the country.) The fancy receivers will provide highly accurate measurements at coarse resolution, and the cheaper receivers will fill in the gaps.<\/p>\n

As the eclipse passes overhead, the GPS receivers will record how much radio waves from satellites are slowed down and bent on their way to Earth, which Semeter and his team will use to measure the density of the plasma. They will then attempt to use the plasma measurements to create images of the ionosphere during the eclipse, with each GPS measurement acting like a single pixel of a digital photo.<\/p>\n

\u201cWe\u2019ll be able to hopefully see all kinds of wave phenomenon and adjustments in the atmosphere caused by the eclipse,\u201d Semeter says, adding that, for example, there will be a cold spot inside the eclipse and a hot spot outside, which could create instabilities in the ionosphere that launch waves away from them. He is also hoping to capture \u201cbow waves\u201d and \u201cstern waves\u201d created as the eclipse moves through space, named for their similarity to the waves a boat produces as it moves through water. \u201cAnd there is, of course, possible discovery,\u201d Semeter says. \u201cWe\u2019ve never had measurements like the type we\u2019re trying to make.\u201d<\/p>\n

Beyond scientific discovery, there are also practical reasons for learning more about these effects on the ionosphere, which are a form of \u201cspace weather.\u201d Small-scale variations in the ionosphere, like waves created by the eclipse, can degrade the accuracy of satellite navigation systems and may even cause GPS signals to be lost completely.<\/p>\n