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![]() by Staff Writers Stanford CA (SPX) Jul 15, 2021
The sun provides a daunting source of electromagnetic disarray - chaotic, random energy emitted by the massive ball of gas arrives to Earth in a wide spectrum of radio frequencies. But in that randomness, Stanford researchers have discovered the makings of a powerful tool for monitoring ice and polar changes on Earth and across the solar system. In a new study, a team of glaciologists and electrical engineers show how radio signals naturally emitted by the sun can be turned into a passive radar system for measuring the depth of ice sheets and successfully tested it on a glacier in Greenland. The technique, detailed in the journal Geophysical Research Letters on July 14, could lead to a cheaper, lower power and more pervasive alternative to current methods of collecting data, according to the researchers. The advance may offer large-scale, prolonged insight into melting ice sheets and glaciers, which are among the dominant causes of sea-level rise threatening coastal communities around the world.
A sky full of signals By contrast, the researchers' proof of concept uses a battery-powered receiver with an antenna placed on the ice to detect the sun's radio waves as they travel down to Earth, through the ice sheet and to the subsurface. In other words, instead of transmitting its own signal, the system uses naturally occurring radio waves that are already traveling down from the sun, a nuclear-powered transmitter in the sky. If this type of system were fully miniaturized and deployed in extensive sensor networks, it would offer an unprecedented look at the subsurface evolution of Earth's quickly changing polar conditions, the researchers say. "Our goal is to chart a course for the development of low-resource sensor networks that can monitor subsurface conditions on a really wide scale," said lead study author Sean Peters, who conducted research for the study as a graduate student at Stanford and now works at the MIT Lincoln Laboratory. "That could be challenging with active sensors, but this passive technique gives us the opportunity to really take advantage of low-resource implementations."
A random advantage In their test on Store Glacier in West Greenland, the researchers computed an echo delay time of about 11 microseconds, which maps to an ice thickness of about 3,000 feet - a figure that matches measurements of the same site recorded from both ground-based and airborne radar. "It's one thing to do a bunch of math and physics and convince yourself something should be possible - it's really something else to see an actual echo from the bottom of an ice sheet using the sun," said senior author Dustin Schroeder, an assistant professor of geophysics at Stanford's School of Earth, Energy and Environmental Sciences (Stanford Earth).
From Jupiter to the sun "We started discussing it in the context of Jupiter's moon Europa, but then we realized it should work for observing Earth's ice sheets too if we replace Jupiter with the sun," Schroeder said. From there, the research team undertook the task of isolating the sun's ambient radio emissions to see if it could be used to measure ice thickness. The method involved bringing a subset of the sun's 200- to 400-megahertz radio frequency band above the noise of other celestial bodies, processing massive amounts of data and eliminating man-made sources of electromagnetism like TV stations, FM radio and electronic equipment. While the system only works when the sun is above the horizon, the proof-of-concept opens the possibility of adapting to other naturally occurring and man-made radio sources in the future. The co-authors are also still pursuing their original idea of applying this technique to space missions by harnessing the ambient energy emitted by other astronomical sources like the gas giant Jupiter. "Pushing the frontiers of sensing technology for planetary research has enabled us to push the frontiers of sensing technology for climate change," Schroeder said. "Monitoring ice sheets under climate change and exploring icy moons at the outer planets are both extremely low-resource environments where you really need to design elegant sensors that don't require a lot of power."
![]() ![]() Earth's cryosphere shrinking with every passing year Washington DC (SPX) Jul 02, 2021 The global cryosphere-all of the areas with frozen water on Earth-shrank by about 87,000 square kilometers (about 33,000 square miles), a area about the size of Lake Superior, per year on average, between 1979 and 2016 as a result of climate change, according to a new study. This research is the first to make a global estimate of the surface area of the Earth covered by sea ice, snow cover and frozen ground. The extent of land covered by frozen water is just as important as its mass because the br ... read more
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