Geography of Senior High School: Can we know the population distribution through remote sensing? Why can it be used to estimate the output of agricultural products?

(A) the main characteristics of remote sensing technology

1. A wide range of data can be obtained. The flying height of aerial photography plane used for remote sensing is about 10km, and the satellite orbit height of land satellite is about 9 10km, which can obtain a wide range of information in time. For example, a Landsat image can cover more than 30,000 square kilometers. This kind of macroscopic image is very important for analyzing the earth's resources and environment.

2. The speed of obtaining information is fast and the period is short. Because the satellite orbits the earth, it can get the latest information of various natural phenomena passing through the region in time, so as to update the original information or carry out dynamic monitoring according to the changes of old and new information, which is incomparable to manual field measurement and aerial photogrammetry. For example, Landsat 4 and 5 can cover the earth once every 16 days, and NOAA meteorological satellites can receive images twice a day. Meteorological satellites acquire images of the same area every 30 minutes.

3. Access to information is less restricted by conditions. There are many places on the earth, where the natural conditions are extremely bad and it is difficult for human beings to reach, such as deserts, swamps and mountains. Using remote sensing technology, especially space remote sensing, which is not limited by ground conditions, can obtain all kinds of valuable information conveniently and timely.

4. There are many ways to get information, and there is a lot of information. According to different tasks, remote sensing technology can choose different bands and remote sensing instruments to obtain information. For example, visible light can be used to detect objects, and ultraviolet, infrared and microwave can also be used to detect objects. Using the different penetrability of different wave bands to objects, we can also obtain the internal information of ground objects. For example, the microwave band can also work around the clock in the depths of the ground, under the water, under the ice water body and under the desert.

The amount of information obtained by remote sensing technology is huge, and its processing means are beyond human reach. For example, the TM image of Landsat satellite, a map covering the ground area of 185km× 185km, has a pixel spatial resolution of 30m, a pixel spectral resolution of 28 bits and a data volume of about 6000×6000=36Mb. If all six frequency bands are sent to the computer, the amount of data is:

36Mb×6=2 16Mb

In order to improve the processing speed of this massive data, remote sensing digital image technology has developed rapidly.

At present, remote sensing technology has been widely used in agriculture, forestry, geology, ocean, meteorology, hydrology, military affairs, environmental protection and other fields. In the next decade, remote sensing technology is expected to enter a new stage, which can provide various earth observation data quickly and timely. The spatial resolution, spectral resolution and temporal resolution of remote sensing images will be greatly improved. With the development of space technology, especially the development and mutual penetration of geographic information system and global positioning system technology, its application field will be more and more extensive.

Remote sensing, in a broad sense, refers to the technology of detecting and sensing objects or things from a distance. That is, without direct contact with the object itself, information (such as electric field, magnetic field, electromagnetic wave, seismic wave, etc. ) is detected and received by instruments (sensors) from a distance, and the attributes and distribution characteristics of objects are identified through information transmission and processing analysis.

Usually, remote sensing refers to air-to-ground remote sensing, which is a comprehensive technology to detect electromagnetic wave (radiation) information on the earth's surface through sensors on different working platforms (such as towers, balloons, airplanes, rockets, artificial earth satellites, spacecraft, space shuttles, etc.) far away from the ground. ) and detect and monitor the earth's resources and environment through information transmission, processing and interpretation.

At present, remote sensing has formed a multi-level, multi-angle and multi-field observation system to detect and monitor the world from the ground to the air, even to the space, from information data collection, processing to interpretation and application, and has become an important means to obtain information on the earth's resources and environment.

The application of remote sensing in geography has further promoted the research and development of geography and brought geography into a new stage of development.

The application of remote sensing information is the ultimate goal of remote sensing. Remote sensing application should choose appropriate remote sensing information and its working methods according to the needs of professional objectives in order to achieve better social and economic benefits.

Remote sensing technology system is a complete unity. It is based on modern science and technology such as space technology, electronic technology, computer technology, biology, earth science and so on, and it is a powerful technical guarantee for completing the remote sensing process.

3) remote sensing principle

The propagation of vibration is called wave. The propagation of electromagnetic vibration is electromagnetic wave. The wave band of electromagnetic wave can be divided into: γ-ray, X-ray, ultraviolet ray, visible light, infrared ray, microwave and radio wave from short to long. The shorter the wavelength of electromagnetic wave, the stronger the penetration. The electromagnetic wave band used in remote sensing detection is the spectral band from ultraviolet, visible light, infrared to microwave. As the source of electromagnetic radiation, the light emitted by the sun is also electromagnetic wave. Sunlight must pass through the earth's atmosphere when it reaches the earth's surface from space. When sunlight passes through the atmosphere, it will be affected by the absorption and scattering of sunlight by the atmosphere, thus attenuating the energy of sunlight passing through the atmosphere. However, the absorption and scattering of sunlight by the atmosphere changes with the wavelength of sunlight. Usually, the spectral section with high transmittance when sunlight passes through the atmosphere is called the atmospheric window. The spectral bands of the atmospheric window mainly include ultraviolet, visible light and near infrared bands. Any object (i.e. target) on the ground, such as atmosphere, land, water, vegetation and artificial structures, has the characteristics of reflecting, absorbing, transmitting and radiating electromagnetic waves when the temperature is higher than absolute zero (i.e. 0 k =-273. 16℃). When sunlight hits the earth's surface from space through the atmosphere, objects on the ground will reflect and absorb electromagnetic waves composed of sunlight. Because the physical and chemical characteristics of each object and the wavelength of incident light are different, their reflectivity to incident light is also different. The reflection law of various objects to incident light is called the reflection spectrum of objects.

(v) Characteristics of remote sensing technology

As a comprehensive earth observation technology, the emergence and development of remote sensing is not only the objective need for people to know and explore nature, but also has incomparable characteristics with other technical means. The characteristics of remote sensing technology can be summarized as follows: 1, wide detection range and fast data acquisition. Remote sensing can observe the earth in a large area from the air or even space in a short time and obtain valuable remote sensing data from it. These data expand people's visual space, create extremely favorable conditions for macroscopically grasping the present situation of things on the ground, and provide valuable first-hand information for macroscopically studying natural phenomena and laws. This advanced technical means is irreplaceable by traditional manual operation. 2. It can dynamically reflect the changes of things on the ground. Remote sensing detection can periodically and repeatedly observe the same area, which is helpful for people to discover and dynamically track the changes of many things on the earth through the obtained remote sensing data. At the same time, study the changing law of nature. Especially in monitoring weather conditions, natural disasters, environmental pollution and even military targets, the application of remote sensing is particularly important. 3. The data obtained are comprehensive. At the same time, remote sensing data covering a large area are obtained. These data comprehensively show many natural and human phenomena on the earth, macroscopically reflect the shape and distribution of various things on the earth, truly reflect the characteristics of geology, geomorphology, soil, vegetation, hydrology, artificial structure and so on, and comprehensively reveal the correlation between geographical things. And these data have the same trend in time.