(a) Overview of remote sensing development
The development of remote sensing can be divided into two stages: the first stage is aerial remote sensing. During World War I, telescopes and cameras on airplanes were used for reconnaissance. After World War II, aerial remote sensing has developed continuously, and now it has become an important means of military reconnaissance and natural resources investigation. The second stage is space remote sensing. 1957, the former Soviet Union launched the first man-made earth satellite, which opened a precedent for exploring the earth from outer space. In 1960s, NASA launched weather satellites such as Rain Cloud and manned spacecraft such as Apollo, and took the first photos of Earth satellites with cameras. After a long period of preparation, especially after studying the spectral characteristics of various ground objects and the technology of data processing, analysis and interpretation of remote sensing images, the United States launched the first Earth Resources Satellite (ERTS), 1972, on July 23rd, and then launched the second batch of Earth Resources Satellite (LANDSAT). 1998, LANDSAT7 launch; 1 In September, 1999, the United States launched a commercial IKONOS satellite with a resolution of1m, which indicates that American civil remote sensing is far ahead of the world. At present, the United States, Russia, France, Canada, Japan, Britain, India and medium-sized countries have become more mature countries in the world in the application of remote sensing technology.
(2) Remote sensing technology and its characteristics
1. Contents of remote sensing technology
Remote sensing is a process of target reflection radiation → medium transmission → remote sensor → information processing and application under the action of energy. Various technical means used to realize this process are collectively referred to as remote sensing technology, which specifically includes the following contents:
(1) Remote sensing technology is a technology that specializes in manufacturing equipment for sensing and collecting target information.
(2) Information transmission technology is a technology to study how to transmit the information collected and recorded by the remote sensor to the information processing center.
(3) On-site sampling technology is a technology that specializes in studying the characteristics of collected target information and provides a basis for distinguishing targets when processing current information.
(4) Information processing technology is an analysis, interpretation and application technology, including information data compression, transmission and correction technology and image display and recording technology.
(5) Identification, analysis and interpretation technology and information storage and application technology.
2. The turning point of remote sensing technology
The main body of remote sensing technology is space remote sensing technology, such as resource and environment monitoring, weather forecasting and other typical technologies. The United States launched the earth resources technology satellite in the early 1970s, and later China successfully launched the meteorological satellite. Space remote sensing technology has the following main features:
(1) has a large amount of information.
(2) The data is novel and can quickly reflect the dynamic changes.
(3) The information obtained is rich in content.
(4) Quick drawing.
(5) Access to information is convenient, all-day, all-weather, and not limited by terrain.
These characteristics not only make a new leap in human understanding of the universe and nature, but also greatly enhance human ability to transform nature, develop and protect resources.
Space remote sensing technology can obtain all kinds of large, medium and small-scale remote sensing images through remote sensing platforms at a height of several million kilometers, which can be called modern remote sensing technology.
(3) Hot spots of remote sensing development
The development of 1. sensor is deepening day by day.
(1) The resolution of remote sensing is increasingly diversified, and remote sensing technology is developing in both macro and micro directions. In order to meet the needs of accurate detection of objects or large-scale research purposes, most satellite sensors (2 1) launched in the late 1990s and early 20th century pay attention to resolution as an important index to obtain information. The spatial resolutions of the radar satellites launched by Canada in1995165438+10 are/kloc-0, 28, 35 and 50/ 100 respectively, and the scanning widths are 50 km and/kloc-0 respectively. The ground resolutions of EROS-A and EROS-B launched by Israel are 2m and 1m respectively, and the scanning widths are 1 1km and 30km respectively.
At present, it is generally believed that the resolution can be improved by narrowing the scanning range and reducing the satellite height under the condition that the basic technical conditions of the satellite remain unchanged. Taking LANDSAT5 of the United States as a reference, the scanning range of French SPOT and Israeli EROS-A and EROS-B satellites is reduced and the resolution is improved. At present, the resolution of various remote sensing detectors has developed from kilometer level and hundred meters level to meter level and decimeter level, forming an image pyramid for observing the earth and its space, providing rich information sources for studying various natural geographical environments and promoting the continuous development of remote sensing and related disciplines.
(2) The sensing belt is more detailed. The frequency band of the sensor is an important parameter to measure the performance of the sensor. According to different research purposes, many sensors have set up special bands, and the band division is more accurate.
RADARSAT has 25 kinds of beams (FL ~ F5, S 1 ~ S7, W 1 ~ W3, SNl~SN2, SWl, H 1 ~ H6, L 1), and the SAR data acquisition time is JERS-/Kloc-0. The EOS Earth Observation System Space Station, which NASA plans to launch in 1998, is equipped with a 64-band medium-resolution imaging spectrometer of 0.40 ~1.04/micron, a 92-band high-resolution imaging spectrometer of 0.40 ~ 2.50 micron,1.4ghz (L-band) and 6. There are also EOS-SAR synthetic aperture radars with different polarization modes, including L-band (24 cm), C-band (5.7 cm) and X-band (3. 1 cm). It can be seen that the increase and subdivision of the band plays an extremely important role in improving the detection accuracy and enhancing the detection purpose of the sensor.
(3) Sensors are becoming more and more specialized. Many remote sensing platforms carry special sensors for predefined research objects and targets. For example, the ERS-2 satellite launched by the European Space Agency (ESA) in April 1995 is equipped with an active microwave remote sensing system (AMl) consisting of synthetic aperture radar (SAR) and wind scatterometer. In addition, it is equipped with radar altimeter, infrared scanner, global ozone monitoring spectrometer, microwave detector, precision rangefinder and laser reflector, which provides wealth for multi-level and multi-directional research on environmental problems.
At present, many sensors have clear uses and professional characteristics, such as sensors for studying seawater temperature, sensors designed for geological exploration, and sensors for studying vegetation changes. The stronger the professional characteristics of sensors, the higher the accuracy of research and the deeper the special research.
2. The application field is wider.
Since the late 1990s, remote sensing has gone far beyond the narrow scope of its initial development and is developing in many directions and levels.
(1) The research on resources and environment is very active. Soil science research is one of the most widely used fields of remote sensing. For this reason, the Seventh Committee of the International Society of Photogrammetry and Remote Sensing set up 10 working groups on renewable resources, geological and mineral resources, land degradation and desertification, disaster loss and environmental pollution, human settlement, terrestrial ecosystem monitoring, ice and snow, ocean and coastline monitoring, global monitoring, etc., which reflected the focus and development direction of remote sensing of resources and environment to varying degrees.
In the new century, survival and development have become the main problems facing mankind. All countries in the world are trying to control the environment and reduce disasters as the focus of future research, and remote sensing technology has great advantages. LANDSAT of NASA, SPOT of France and ERS of ESA all take the earth as the research object, providing basic data for scientific and technical personnel to study ozone, vegetation, seawater temperature and atmospheric conditions, and also providing more detailed experimental information and image data for human beings to study the earth and protect their homes.
(2) Remote sensing of the universe has been further strengthened. At present, the development of remote sensing has gone beyond the scope of "air-to-ground" and developed into "ground-to-air" and "air-to-air". The Mars program jointly carried out by the United States, Russia and France is a representative in the field of space remote sensing. At present, not only the atmosphere, hydrosphere and lithosphere of the whole earth are studied, but also the detection range is extended to the space outside the earth.
With the development of remote sensing in the universe, people's cognitive level and ability have been continuously improved, and at the same time, it has helped people explore a series of important academic issues. From the analysis of the images and data sent back by the Mars probe, scientists have obtained a lot of basic information that is helpful to study the origin of life, the formation of stars, the evolution of the universe and other major issues, and also to further study the geotectonics and the exploration of cosmic resources.
3. Integration of various high technologies.
"3S" technology integration is an active field at present. In just a few years, digital photogrammetry system (DPS) and expert system (ES) have quietly merged with "3S" technology, and the so-called "5S" technology has emerged. The integration of these technologies is the product of the development of computer science and space science. At the same time, it also promotes the mutual penetration and integration of remote sensing and related disciplines (such as earth science, environmental science, urban science, management science, etc.). ), and then form a new frontier discipline-geographic informatics, which has become an important part of information science and information industry. The development of information science, in turn, affects almost global changes in production methods and lifestyles, as well as the development of science and technology itself. The widespread popularity of the Internet makes information acquisition and enjoyment faster, and makes computers penetrate into the fields of aided design, aided processing, aided testing and analysis, and management.
(D) the combination of geographic information system and remote sensing
The combination of GIS and RS mainly shows that RS is an important information source of GIS, and GIS is a powerful technical guarantee for processing, analyzing and applying remote sensing data. The key technology of combining the two is the interface between raster data and vector data: the data of remote sensing system generally adopts raster format, and its information is stored in the form of pixels; GIS data are mainly stored in the form of graphic vectors and points, lines and surfaces. The difference between them is that image data and cartographic data use different spatial concepts to represent the same information in the objective world.
For the strategy of integrating RS and GIS, Ehlers and others put forward three development stages: the first stage, the two software modes are connected by data exchange format; In the second stage, the two software modes have the same user interface and are displayed simultaneously; The third stage is the software body with compound processing function.
(v) Practical application of remote sensing in earth science.
In recent years, there are many researches on the integration of rs and GIS in China, which have gone through a process from preliminary discussion to gradual maturity. Its application mainly includes two aspects: first, remote sensing data is used as the information source of geographic information system; Secondly, GIS provides RS with a means of spatial data management and analysis. Zhang Jixian put forward earlier in China that integrating geoscience knowledge and remote sensing data in GIS information can improve the accuracy of remote sensing classification and eliminate some disadvantages of applying single remote sensing image interpretation. However, the combination of the two has the problem of data conversion, so the research of the corresponding software is also very important. In the process of applying GRAMS, an integrated system of RS and GIS, Ren Xiaohu and others think that although the software can achieve seamless integration on the surface, as far as its internal format conversion is concerned, it can not realize the * * * enjoyment and free conversion of data. At first, there were many researches on how remote sensing can provide data and information for GIS. For example, in the process of urban and rural planning in Liu Binyi, remote sensing is used as the main information source to collect regional information, and planning and design are carried out on this basis. In the land evaluation of Wuchang, Hubei and Ansai, Shaanxi, Xiang Facan also used the values of evaluation factors obtained by rs as the information source for composite superposition, and on this basis, it was processed by GIS, realizing dynamic and rapid land resource evaluation. Specific to the complete combination of RS and GIS and the conversion of data format, Qin Zhiyuan proposed the combination mode of "combination cone" and mixed Freeman chain code structure to solve this problem.
At present, the integrated application technology of RS and GIS has gradually matured, and there are related application reports in vegetation classification, disaster estimation, image processing and so on. In the research of applying the spatial analysis function of GIS to provide spatial data management and analysis for RS data, the spatial distribution of DEM data, the climate and environment of GIS are mainly considered. For example, Liu Jiyuan and others discussed the feasibility of combining geographic data provided by GIS with remote sensing data in the comprehensive classification of vegetation in Northeast China. They tried to quantify the three main indicators affecting regional vegetation coverage according to a certain ground grid system and mathematical model in GIS environment to generate digital geoscience images, which were combined with NOAA-AVHRR data after optimization and compression, and achieved good results. In the study of glacier change in Qinghai-Tibet Plateau, Li Zhen and others used the remote sensing data of RBV, MSS and TM as information sources to extract the glacier boundary and form a glacier boundary map. Using GIS as a tool to analyze the change of this glacier group, the change law of glaciers north of Gefeng in Bukata is obtained. The technology of comprehensive application of GIS and RS for drought monitoring and land use classification is also quite mature. Huang made full use of the advantages of RS, GIS, computer graphics technology and network technology to develop the "dynamic decision-making consultation system for remote sensing satellites in the Yangtze River Delta", which represents a new method of combining RS and GIS and synthesizing other multidisciplinary technologies.