If the Global Positioning System (GPS) is a great invention, you should have no objection? With GPS on your smartphone, you can go anywhere with confidence, as if you are a “living map”. But did you know? In addition to navigation, GPS has many hidden functions, and these functions are of great value.
GPS is composed of a group of satellites that send signals to the surface of the earth. Four or more satellites in different directions in space simultaneously send signals to the receiver in your hand, and determine your location by measuring the time difference between the arrival of these signals. The hidden function of GPS also comes from this.
Don’t be afraid of natural disasters
In 2003, Christina Larsen, a geologist at the University of Colorado at Boulder, was studying the seismic waveforms of the Alaska magnitude 7.9 earthquake in North America. He accidentally discovered the waveform recorded by the seismograph and the GPS 140 kilometers away from the epicenter of the earthquake. The recorded waveforms are very consistent, the amplitude and frequency of the seismic waves are the same, which inspired people to use GPS to warn of earthquakes.
Using GPS to warn earthquakes has great advantages. Today, GPS satellites are covered all over the world, and the monitoring is almost 360° without dead angles; the microwave wavelength emitted by GPS is only 20 cm, and the energy and accuracy are relatively high; GPS receivers update targets The speed of the position is also very fast, which can be updated more than 20 times per second. In other words, when people set the location to be located at the epicenter or the edge of plate movement, they can monitor how the ground moves during the earthquake in real time.
Since then, GPS has begun to show its skills in monitoring earthquakes. In the United States, GPS early warning has become one of the important technical methods in the earthquake early warning system. It can not only predict the magnitude of an earthquake, but also inform citizens in cities far away from the epicenter of whether the earthquake will affect them and when they will arrive. “Their city. Chile has also been building its GPS network to obtain earthquake warning information faster and more accurately. Their GPS early warning system successfully predicted the 2010 magnitude 8.8 Mohr earthquake, the 2014 magnitude 8.2 Iquique earthquake, and the 2015 magnitude 8.3 Iliapel earthquake.
GPS can also help us monitor other natural disasters, such as the “twin brothers” of earthquakes-volcanic eruptions.
GPS near the port can be used as a tide gauge
Why are volcanoes the “twin brothers” of earthquakes? Because during an earthquake, the violent movement of the surface will make the volcano’s magma “just about to move.” Before a volcanic eruption, when magma moves underground, it usually causes the surface to move. Therefore, earthquakes and volcanic eruptions are often “inseparable”. Similar to monitoring the surface movement during an earthquake, by monitoring the surface movement around the volcano, researchers can understand the flow of magma and molten rock. In 2018, before the Kilauea volcano erupted in Hawaii, researchers used GPS to monitor which part of the volcano moved the fastest, and the government used this information to make decisions about where to evacuate residents and tourists.
GPS monitoring data after the eruption is also very useful. Because when the signal is transmitted from the satellite to the ground, it must pass through the volcanic ash and other materials ejected into the air by the volcano, so the signal transmission speed and energy will be affected. By studying the extent to which the signal is affected, scientists can estimate how much volcanic ash is ejected, as well as the direction and speed of their propagation. After knowing these data, the flight path of the aircraft can be modified to make it fly around the volcanic ash to avoid the risk of volcanic ash particles blocking the jet engine.
Noise is useful
As mentioned earlier, the GPS receivers commonly used in our navigation mainly receive signals transmitted by GPS satellites in the sky, but inevitably, some of the microwaves emitted by satellites will be scattered to the ground, and then bounced by the ground, and finally by our GPS received. In the past, we classified this type of reflected signal as noise, and weakened the effect of noise by strengthening the microwave directly emitted by the satellite. But later, scientists discovered that this type of noise also has a role.
In 2005, Larson started observing the frequency of the signal reflected from the ground and tried to separate the reflected signal from the signal directly reaching the receiver. She found that by analyzing the speed and energy of the reflected signal, it is possible to judge the situation near the ground, such as how much snow has accumulated on the ground. The more snow on the ground, the shorter the distance between the echo and the receiver. The GPS receiver can be used as a snow sensor to measure snow depth.
Now, this method has been used in the Arctic and Antarctic. Geologist Matt Siegfried of the Colorado School of Mines used data from 23 GPS stations in West Antarctica to analyze the snow cover from 2007 to 2017. No weather monitoring stations have been established in the two poles. Scientists cannot find the weather reports for these years, but with this method, they can analyze the changes in the annual snowfall in the two poles. By comparing the changes in annual snowfall, we can assess the impact of global warming, and compare it with the annual amount of snow melting at the poles, and how many more years the polar ice caps can support, and we have more credible prediction data.
In addition to monitoring changes in the amount of snow on the ground, GPS is also very useful in monitoring changes in groundwater levels.
In July 2019, physicist John Gelzka of the UNESCO Institute of Geophysics installed rows of GPS receivers at the junction of the Ganges and Brahmaputra rivers in Bangladesh From a distance, they look like rows of protection forests, and their functions are actually similar to protection forests. The soil in this place is loose and the river scours strong, so floods happen frequently. Gerzka’s purpose of installing these GPS is to measure whether the soil at the bottom of the river is firm, whether the land is sinking and the depth of the river changes, which helps to monitor the time of flooding in the area and find places that are vulnerable to flooding. By measuring the time difference of noise received by GPS in different places, scientists will be able to judge the depth of the river and the ground.
Changes in the sky
Similar to the barrier effect of volcanic ash, atmospheric water vapor, charged particles and other substances can also affect the propagation of GPS signals in the atmosphere, which has led researchers to new discoveries.
Using GPS to calculate the amount of water vapor in the atmosphere can predict precipitation. In July 2013, Anglin Moore, a meteorologist at the California Institute of Technology, used GPS data to track the movement of a stream of water vapor in the atmosphere sufficient to form a torrential rain. When he noticed that this vapor was moving from the ocean to the mountains, he promptly warned the mountain people. After 17 minutes, the flash flood broke out.
The atmosphere above 60 kilometers from the ground is filled with many charged electrons and ions, which we call the ionosphere. GPS signals will be scattered and refracted when passing through the ionosphere, and the transmission direction and speed will also be affected. Scientists can use GPS data to track changes in the ionosphere. The huge force generated during a tsunami will cause particles in the ionosphere to accelerate and change their charging conditions. That is to say, when GPS detects changes in the ionosphere, it is likely to indicate that a tsunami is about to occur. Scientists used this method to successfully predict three tsunamis in the Kuril Islands in Russia in 2006, Tohoku Town in Japan in 2011 and Haida Guay Island in Canada in 2012.
Scientists can even use GPS to study the effects of a total solar eclipse. In August 2017, researchers from the National Institute of Geophysics used data from GPS stations across the United States to calculate the changes in the number of electrons in the ionosphere. They found that when the moon blocks sunlight, the number of electrons in the ionosphere will increase significantly. Decline will affect the reception of all electromagnetic wave signals including GPS signals.
Earthquake warning, volcano monitoring, groundwater monitoring, atmospheric change tracking… When you use GPS in dense forests, icy snowy areas, and storms, you may hear the “GPS signal weak” prompt, because there are many obstacles around the signal. Things and receiving a lot of interference noise, but you will not know that there is so much information hidden in these “sounds” that interfere with our navigation.