GPS global positioning system is an expert in city navigation, people can even rely on GPS equipment to travel through remote areas on foot.
A series of satellites send signals to the surface of the earth, and GPS receivers determine your location by measuring the time of arrival of the signals, accurate to within 1 to 10 meters, and more expensive receivers can accurately locate to centimeters or even millimeters.
Using this fine information, coupled with algorithms that analyze the signal, the researchers found that GPS can tell them more about the planet.
In the past ten years, GPS has helped scientists map out how the ground moved during earthquakes and provided early warning for natural disasters such as mountain torrents and volcanic eruptions. Researchers even transformed some GPS receivers into snow sensors, tide gauges, and other unexpected measurement tools.
Kristine Larson, a geophysicist from the University of Colorado Boulder, said: "When I first mentioned these applications, people thought I was crazy, but in the end we did it."
1. Detect earthquakes
For centuries, scientists have relied on seismographs to assess the magnitude and damage of earthquakes. Seismographs can measure the degree of ground shaking, but GPS is different. It tracks geological processes, such as the speed at which crustal plates rub against each other.
Most people believe that GPS cannot accurately and quickly measure the location of an earthquake, so it cannot be used to assess earthquakes. But it turns out that scientists can extract additional information from the signals sent to the earth by GPS satellites.
These GPS signals are divided into two parts. One is a code, which is a series of 0s and 1, and the other is a carrier signal, which is responsible for transmitting the code. The wavelength of the carrier signal is short, only 20 centimeters, but the wavelength of the code is longer, which can reach tens or hundreds of meters, so the carrier signal can accurately locate a point on the earth's surface with high resolution.
Engineers have also increased the speed at which the GPS receiver can update its position, that is, refreshing the data at a frequency of 20 times per second or faster. The researchers realized that they could make precise measurements so quickly, and they began to use GPS to study earthquakes.
In 2011, researchers obtained GPS data from Japan's 9.1 magnitude earthquake. The data showed that the seafloor moved an astonishing 60 meters during the earthquake.
2. Monitoring volcanoes
Many volcanoes have GPS receivers around them, because the movement of magma underground usually causes the surface to move. By monitoring the rise and fall of GPS around the volcano, researchers can understand where the lava is flowing.
Before the Kilauea volcano erupted in Hawaii, researchers used GPS to understand which parts of the volcano moved the fastest, and then used this information to decide where to start evacuation.
Even after the eruption of a volcano, GPS data is useful. Signals must pass through volcanic eruptions in order to be transmitted from the satellite to the ground. In 2013, several research teams discovered that the signal was distorted shortly after the eruption of the Redoubote volcano in Alaska.
Based on these distorted data, scientists can estimate the amount and speed of volcanic ash ejection.
3. Detect snowfall
A typical GPS receiver, in addition to signals from overhead satellites, can also receive signals reflected from the ground.
For many years, scientists have thought that these signals are just noise, but starting about 15 years ago, they discovered that through the frequency of the ground reflected signals and the combination of these signals, they can infer the surface properties of echo reflections. Larson said: "We just reverse-engineered the echo."
This method allows scientists to understand how much moisture is in the soil or how much snow has accumulated on the ground (the more snow on the ground, the shorter the distance between the echo and the receiver). GPS stations can even be used as sensors to measure the depth of snow, such as being built in mountainous areas where snow is the main water resource.
4. Analyze the atmosphere
In addition to the applications mentioned above, GPS can also be used to sort out the information contained in the sky.
The propagation of GPS signals in the atmosphere is delayed by water vapor, charged particles and other factors. Therefore, scientists use GPS to study the water vapor content in the atmosphere, and then calculate how much water will fall from the sky in a downpour. . During a storm in July 2013, meteorologists used GPS data to track the movement of monsoon water vapor. It turned out that this was a warning issued 17 minutes before the flash flood.
When GPS signals pass through the ionosphere, they are also affected by charged particles. Therefore, scientists use GPS data to track changes in the ionosphere, because changes in the atmosphere produced by the tsunami will continue to spread to the ionosphere. One day, this technology may even become part of a tsunami warning.
