Tag: nature

Researchers develop 10-cm accuracy navigation system

Researchers at Delft University of Technology, Vrije Universiteit Amsterdam and VSL have developed an alternative positioning system that is more robust and accurate than GPS, especially in urban settings.

The aim of the project — SuperGPS — was to develop an alternative positioning system that makes use of the mobile telecommunication network instead of satellites and that has better accuracy than GPS.

The working prototype that demonstrated this new mobile network infrastructure achieved an accuracy of 10 centimeters.

The new technology is important for the implementation of a range of location-based applications, including automated vehicles, quantum communication and next-generation mobile communication systems.

Much of our vital infrastructure relies on GNSS. Yet systems that rely on satellites have limitations and vulnerabilities. For instance, their radio signals are weak when received on Earth, making accurate positioning no longer possible if the radio signals are reflected or blocked by buildings.

“We realized that with a few cutting-edge innovations, the telecommunication network could be transformed into a very accurate alternative positioning system that is independent of GPS,” said Jeroen Koelemeij of Vrije Universiteit Amsterdam. “We have succeeded and have successfully developed a system that can provide connectivity just like existing mobile and Wi-Fi networks do, as well as accurate positioning and time distribution like GPS.”

Illustration: TU Delft / Stephan Timmers

One innovation is to connect the mobile network to a very accurate atomic clock so that it can broadcast perfectly timed messages for positioning, just like GPS satellites do with the help of the atomic clocks they carry on board. These connections are made through the existing fiber-optic network.

“With these techniques, we can turn the network into a nationwide distributed atomic clock — with many new applications such as very accurate positioning through mobile networks,” said Erik Dierikx, VSL. “With the hybrid optical-wireless system that we have demonstrated now, in principle anyone can have wireless access to the national time produced at VSL. It basically forms an extremely accurate radio clock that is good to one billionth of a second.”

The system also employs radio signals with a bandwidth much larger than commonly used. “Buildings reflect radio signals, which can confuse navigation devices. The large bandwidth of our system helps sorting out these confusing signal reflections, and enables higher positioning accuracy,” explained Gerard Janssen of Delft University of Technology. “At the same time, bandwidth within the radio spectrum is scarce and therefore expensive. We circumvent this by using a number of related small bandwidth radio signals spread over a large virtual bandwidth. This has the advantage that only a small fraction of the virtual bandwidth is actually used and the signals can be very similar to those of mobile phones.”

The results of the peer-reviewed research have been published in Nature.

Photo: TU Delft / Frank Auperlé

November 21, 2022
China investigates improving GNSS timing with lasers

Image: fotojog/iStock/Getty Images Plus/Getty Images

Chinese scientists say they have succeeded in an experiment that could improve satellite navigation and redefine the second as a unit of time, reports the South China Morning Post.

The scientists performed the experiment in Urumqi, capital of Xinjiang Uygur autonomous region in western China. They placed two terminals in laboratories 113 km (70 miles) apart. Each terminal was equipped with a laser, a telescope and two optical frequency combs that measure exact frequencies of light. Laser pulses sent between the terminals allowed researchers to confirm the time.

The research team was led by quantum physicist Jian-Wei Pan at the University of Science and Technology of China (USTC).

Sending signals over long distances would enable a global network of optical clocks that can help improve the accuracy of satellite navigation services.

China also is sending three atomic clocks to its Tiangong space station to establish a space-based timekeeping system of exceptional accuracy. The clocks can work together to measure time with 10^-19 stability, missing only one second every few billion years, and is expected to be thousands of times more accurate than a hydrogen maser.

November 7, 2022
Esri Field Notes App Answers Questions with Geography
Smartphone users now have access to Field Notes—Earth, a new mobile app from Esri that employs the power of geography to answer questions about locations throughout the world. Built using Esri’s AppStudio for ArcGIS, the free app allows anyone to discover interesting facts about population, nature and physical landscapes for any location on Earth.

“Field Notes—Earth leverages the tremendous capabilities of geographic information to describe the world in detail,” said Esri president, Jack Dangermond. “Tools like these update and transform our understanding and expectations in ways that help us be wiser citizens of the planet.”

With an intuitive design available on Android and iOS devices, the app gives users the option to discover answers to questions about their hometown, current residence, or any place of interest. It lets them compare these findings to an additional location.

After selecting an initial place via current location, search, or by dropping a pin on a map, the app reveals geographic insights for three categories — Natural, Physicaland People. Sample questions include:
- How crowded is it in this location?
- How close am I to a recent earthquake area?
- What is the predicted 2050 change in average temperature?
“Whether you are relocating, are an educator looking for a new teaching resource, or just curious about the world around you, the app reveals insights into the complexity of humanity’s relationship with Earth for everyone to enjoy,” said Sean Breyer, ArcGIS content program manager at Esri.

In addition to exploring 18 questions, users can click on any answer for more details and to learn how the selected locations relate to the rest of the world’s landscape and populations. The app reveals, for example, that the majority of people live in very hot climates and more than 40 percent of the Earth’s soil is poor for most crops.

Field Notes—Earth uses maps from Esri’s Living Atlas of the World, including the World Ecological Land Units map that shows the Earth’s complex ecosystems; the new World Seafloor Geomorphology map that reveals the complex role oceans play in Earth systems; and the World Population Estimate map that shows where people live.

Esri’s Content Team created the app using AppStudio for ArcGIS, which lets you build an app once and have it automatically ready for Android, iOS, Windows, OS X, and Linux.

The app is available for free download in the Apple App Store and Google Play.
August 13, 2015
GPS Helps Solve Mystery of Sliding Rocks

Rarely formed sheets of ice push rocks across a dry lake in Death Valley.

In Racetrack Playa in Death Valley, California, hundreds of rocks — some weighing as much as 700 pounds — seem to have been dragged across the ground, leaving synchronized trails that can stretch for hundreds of meters. Though many phenomena were speculated (hurricane-force winds, dust devils, slick algal films, thick sheets of ice), no one knew what caused the movement.

To solve the mystery, in 2011 a team of researchers led by paleobiologist Richard Norris, Scripps Institution of Oceanography, UC San Diego, began monitoring the rocks remotely. The research team fit 15 similar rocks with custom-built, motion-activated GPS units (the National Park Service disallowed use of native rocks) and installed a high-resolution weather station capable of measuring gusts to one-second intervals. Then — in what Ralph Lorenz of the Applied Physics Laboratory at the Johns Hopkins University suspected would be “the most boring experiment ever” — the researchers waited for something to happen.

In December 2013, Richard Norris and co-author and cousin Jim Norris discovered that the playa was covered with a pond of water three inches deep. Shortly after, the rocks began moving.

“Science sometimes has an element of luck,” Richard Norris said. “We expected to wait five or ten years without anything moving, but only two years into the project, we just happened to be there at the right time to see it happen in person.”

Their observations show that moving the rocks requires a rare combination of events. First, the playa fills with water, which must be deep enough to form floating ice during cold winter nights but shallow enough to expose the rocks. As nighttime temperatures plummet, the pond freezes to form thin sheets of “windowpane” ice, which must be thin enough to move freely but thick enough to maintain strength. On sunny days, the ice begins to melt and break up into large floating panels, which light winds drive across the playa, pushing rocks in front of them and leaving trails in the soft mud below the surface.

“On December 21, 2013, ice breakup happened just around noon, with popping and cracking sounds coming from all over the frozen pond surface,” said Richard Norris. “I said to Jim, ‘This is it!’”

The rocks moved under light winds of about 3-5 meters per second (10 miles per hour) and were driven by ice less than 3-5 millimeters (0.25 inches) thick, a measure too thin to grip large rocks and lift them off the playa, which several papers had proposed as a mechanism to reduce friction. Further, the rocks moved only a few inches per second (2-6 meters per minute), a speed that is almost imperceptible at a distance and without stationary reference points.

“It’s possible that tourists have actually seen this happening without realizing it,” said Jim Norris. “It is really tough to gauge that a rock is in motion if all the rocks around it are also moving.”

Individual rocks remained in motion for anywhere from a few seconds to 16 minutes. In one event, the researchers observed rocks three football fields apart began moving simultaneously and traveled over 60 meters (200 feet) before stopping. Rocks often moved multiple times before reaching their final resting place. The researchers also observed rock-less trails formed by grounding ice panels — features that the Park Service had previously suspected were the result of tourists stealing rocks.

“The last suspected movement was in 2006, and so rocks may move only about one millionth of the time,” Lorenz said. “There is also evidence that the frequency of rock movement, which seems to require cold nights to form ice, may have declined since the 1970s due to climate change.”

The team’s findings were published in the journal PLOS ONE on August 27.

August 28, 2014