Science in the spotlight this week | Desert lakes seen from space

1. Desert lakes seen from space

Recently, my country's "Jilin-1" optical remote sensing satellite released photos of lakes in the desert taken from space, including famous lakes such as the Crescent Lake in Dunhuang, Gansu, and the Moon Lake in Alxa Left Banner, Inner Mongolia. Such precious and clear "Earth selfies" are rare.

In life, we can take selfies with mobile phones, cameras or other electronic devices, but to take a "selfie" of the earth, the best way is to use satellites. As we all know, artificial satellites operate in space at least 200 kilometers above the ground and have a wide field of view, so they can take relatively complete images of designated areas of the earth. However, the disadvantage is also obvious. Because they are too far from the ground, many details in the picture are difficult to distinguish clearly. The development of remote sensing technology has solved this problem. By collecting, processing and finally imaging the electromagnetic wave information radiated and reflected by distant targets, satellite images with higher detail restoration can be obtained.

Remote sensing satellites are artificial satellites that use this technology. From a classification point of view, remote sensing satellites can be divided into meteorological remote sensing satellites, ocean remote sensing satellites, land remote sensing satellites, resource remote sensing satellites, etc. These satellites can conduct uninterrupted observations of weather, land, and ocean. In the application field, ground monitoring and observation (taking photos) are the most important tasks of remote sensing satellites. However, compared with taking photos directly from our mobile phones by pressing the shutter in our daily lives, remote sensing satellites are slightly more complicated. First of all, satellites are not actually "shooting", but "scanning" the earth. Specifically, remote sensing image data is obtained by adjusting the different angles of the observation instrument and aiming at different locations on the earth. However, due to the high spatial resolution of hyperspectral remote sensing images and the information redundancy caused by the high dimensionality of data (combing of multiple types of data, such as altitude, time, latitude, longitude, color, etc.), it is also necessary to extract and distinguish the specific features in the remote sensing images (such as mountains, rivers, cities, trees, etc. on the ground) in the later stage, so as to obtain high-precision films.

Hotspot sources:

https://s.weibo.com/

Image source:

Jilin-1——Symbiotic Earth

Editor's note: Unlock a new profession - "Space Photographer"

2. There are only 600 wild beavers left in China

Beaver is the second largest rodent in the world (second only to capybara). There are two types of beavers currently in existence. One is the Canadian beaver (also known as the American beaver), which is mainly distributed in North America and has more than 20 subspecies; the other is the Eurasian beaver, which is distributed in Europe and Northern Asia and has 8 subspecies.

The Ulungur River Basin in the Altay region of northern Xinjiang, my country, is home to a group of Mongolian beavers (Eurasian beaver subspecies), which are a national first-class protected wild animal. Beavers are amphibious mammals, but they move slowly and clumsily on land and generally do not move far from the water, which has taught them a unique skill - building dams.

Beavers are considered to be the only animals in the animal kingdom that can purposefully change their habitat to meet their own living conditions. Generally speaking, beavers will not build dams in river basins with abundant water flow and high water speed. Only when the water volume in some tributaries is very small, beavers will choose to build dams to block the water flow in order to prevent the water level from dropping, causing their nests to be exposed to the water and lose their homes.

When beavers build dams, they usually insert strong branches into the bottom of the water first. Sometimes they use trees on the shore or gravel on the riverbed as fixed objects to reduce the collection of branches. In addition, they fill the gaps in the dam with sand and twigs to make it impermeable. In addition, during construction, in order to enhance the pressure resistance of the dam, beavers will build the middle of the dam slightly lower than the two sides, allowing water to flow only from the two banks to reduce the pressure on the dam. They are worthy of being called outstanding "builders" in the animal kingdom.

Dams built by beavers also play an irreplaceable role in conserving water resources. Water stored in dams can provide water and food for other animals during droughts, which means that there is a small ecosystem near each dam built by a group of beavers. In the early history, ancient beaver fossils found in my country showed that the species of beavers in the past were much richer than those of modern beavers (referring to beavers that now live in a certain space on the earth), including 7 genera, and their distribution range was much wider than that of modern Xinjiang beavers. The deciduous and coniferous forest areas of mainland my country, as well as suitable riverside habitats in tundra and grassland areas were once their ideal homes. However, due to habitat degradation and human hunting, their numbers have decreased sharply. Currently, they only exist in some marginal and isolated areas. There are only about 600 Mongolian beavers left in my country.

Hotspot sources:

https://s.weibo.com/

Image source:

The Paper

The editor has something to say: "Is this a "beaver"?

Summarize:

① In fact, for ordinary people like us, we can use remote sensing satellites to view real-time road and vehicle information. If we want to view the scenery of a certain scenic spot, we can also query it through satellite image services. This can be said to be a blessing for people with entanglement disorder;

② The number of beavers in Xinjiang is very small. Researchers have thought about preventing the extinction of the population through artificial breeding. However, because the temperature, ultraviolet rays, and food in artificial breeding cannot reach the conditions in the wild, beavers cannot become pregnant. At present, the population has to be stabilized through wild protection.