As a basic and service industry for national economy and social development, transportation plays an indispensable and important role in the overall planning of the country. The use of new technologies to improve the level and efficiency of all kinds of transportation applications has attracted the attention of the transportation industry.
In the current era, the transportation industry is focused on improving the network, adjusting the structure, optimizing management, and improving services, with the goal of building a smooth, efficient, safe, and green transportation system. With the rapid development of remote sensing and spatial information technologies, as well as the increasingly urgent demand for the acquisition and processing of sensing data with large space-time coverage in transportation applications, the development of remote sensing and spatial information technologies oriented towards transportation applications has great significance and great potential. High-resolution remote sensing data has such advantages as large image coverage, wide detection range, strong timeliness, objective and true information, low cost, and easy access, and has broad application prospects in the survey, design, operation, maintenance, and road environment protection of transportation infrastructure, as well as in the monitoring of transportation disasters. With the development of high-resolution remote sensing satellite technology in China, domestic remote sensing satellites will reach the foreign advanced level in both quantity and image quality, and they have high-resolution observation capabilities in different remote sensing bands. This article first discusses the application of remote sensing technology in the transportation industry at home and abroad, and analyzes the application prospects and details of high-resolution remote sensing technology in China's transportation industry, in hope of giving full play to the application efficiency of domestic satellites, and promoting the industrialization of high-resolution remote sensing data in China's transportation sector.
II. Application Status of Domestic Remote Sensing Technology in Transportation Industry
In the application of remote sensing in highway survey and design, Aerial Photogrammetry and Remote Sensing Co., Ltd. (ARSC), subordinate to the China National Administration of Coal Geology (CNACG), conducted an early-stage line selection study on the Xuanwei–Qujing section (in Yunnan) of Highway G56 using Japanese ALOS satellite remote sensing images, and surveyed the landform, lithology, structure, and adverse geological conditions on the project area. ARSC preliminarily ascertained the distribution of adverse geology along the line corridors, and proposed recommended routes. The Remote Sensing Information Center of the Highway Survey and Design Institute of Shaanxi Province completed a field engineering geology survey of the Yulin–Shenmu Highway using Landsat ETM and QuickBird data combined with field GPS, and identified the engineering geological environment and adverse geological phenomena in the line corridor, providing a sufficient scientific basis for the selection of the Yulin–Shenmu Highway program and the engineering geological evaluation. Given the typical difficulties of steep terrain, geological complexity, and data gaps in the survey and design of the S306 line in Tibet, Zhou Xianbin, Chen Chujiang, et al. studied the multi-scale engineering geological remote sensing of high-resolution IKONOS satellite images for geological line selection using the 3S technology, filling the gap in the basic data of the surveyed area. In the application of remote sensing in highway transportation mapping, the transportation remote sensing information system developed by the Highway Survey and Design Institute of Shaanxi Province in 2003 utilized a wealth of satellite remote sensing images (high-resolution images such as SPOT, SAR and aerial images for Xi'an, Xianyang, and other places) to fully reflect the transportation information of various grades of highways, planned highways, and railways, as well as economic, cultural, resource, and environmental data. Xinjiang Transportation and Communication Information Center extracted basic information of rural highways in Xinjiang using remote sensing technology, providing accurate basic data for the planning, construction, maintenance, and management of rural highways through a combination of automatic extraction and manual extraction. Wuhan University and the Institute of Remote Sensing and Digital Earth at Chinese Academy of Sciences conducted in-depth research on extracting highway network information from remote sensing images from different angles, and put forward many meaningful methods and models, such as automatic extraction of transportation hub information and traffic flow information using high-resolution images. In the application of remote sensing in highway disaster monitoring, Henan's geological surveyors conducted a comprehensive and macro survey of the geological disasters and structural systems along the Yanjing–Mangkang section, using Landsat ETM and data combined with 1:60,000 black and white aerial photographs, providing a scientific basis for road maintenance and governance. The Remote Sensing Application Research Institute of ARSC, CNACG, conducted a survey of geological environment and geological hazards on the national highways 317 and 214 in Tibet, using 1:40,000 to 1:50,000 color infrared aerial photographs, determined the positions of landslides, collapses, and debris flows on the line, and analyzed the degree of damages to the highways, providing a geological basis for highway disaster control in Tibet. China's resource satellite images and aerial photographs combined with the GIS were used to investigate highway disasters of the Tibet-based section of the Sichuan–Tibet Highway, determine the distribution of slides, collapses, and faults, and study their development trends and harm levels, providing detailed and reliable information for the design and decision-making of new highways as well as the management and rectification of existing highway sections. In the application of remote sensing in highway damages, the Chinese Academy of Sciences and other organizations monitored and evaluated the damages to highways and railways located in the Yangtze River and Nen River basins during the 1998 China floods, using remote sensing technology. The Institute of Remote Sensing and Digital Earth at Chinese Academy of Sciences monitored the damages to highways in the 1999 Nantou earthquake in Taiwan and the 2003 Jiashi earthquake in Xinjiang. Given the traffic congestion caused by snow and frost damage in South China in early 2008, the Research Institute of Highway and the National Disaster Reduction Center of the Ministry of Civil Affairs monitored the Chenzhou section in Hunan of the Beijing–Zhuhai Expressway, using radar satellite data. The Institute of Remote Sensing and Digital Earth at Chinese Academy of Sciences and the Research Institute of Highway conducted a remote sensing assessment of detailed damages to highways in the hardest-hit areas caused by the Wenchuan earthquake occurring on May 12, providing a scientific basis in time for highway repair for emergency rescue and post-disaster reconstruction. China has established a number of transportation remote sensing application systems. Some provinces and cities have already carried out remote sensing applications using remote sensing data and achieved good results. However, there is still a large gap compared with foreign integrated applications of high-resolution remote sensing technologies. High-resolution transportation remote sensing applications have not yet been widely promoted in practical systems.
III. Application of High-Resolution Remote Sensing Technology in China's Transportation Industry
1. Application in Highway Network Planning and Design
In view of the great influence, wide coverage, and heavy quantities of highways, high-resolution remote sensing image data can provide basic, intuitive and rich information for tasks such as preparation of functional zoning maps, geological survey, land occupation analysis, and production of construction drawings in the application in highway planning. The application in the planning and design of highway network mainly includes:
1) Production of functional zoning maps and traffic construction drawings: High-resolution remote sensing images can macroscopically reflect the global picture of the highway sections to be constructed, as well as the layout of various natural and cultural factors. Additionally, high spatial resolution enables lean production of drawings with large amounts of information and rich content. Therefore, high-resolution data has become the main information for survey, design and planning in the early stage of highway construction.
2) Geological survey: The high spatial resolution of high-resolution remote sensing images has the advantages of marking fault segments, interpreting geological structures on large-scale landslides, bridges, and tunnels on the ground, and analyzing the information on the alluviation, deposition and shoreline trends of waters. Further, high-resolution data can be used to extract topography, geomorphology, geological structure and geographical information, in order to identify adverse geological phenomena, hidden geological phenomena, special rock-soil and hydrogeology, environmental geology, etc., providing a basis for the selection of route plans and sites of bridges and tunnels.
3) Land occupation analysis and estimation of quantities: During the construction phase of highways, planners can analyze highway land occupation through dynamic contrast of high-resolution remote sensing images and other data. In addition, high-resolution data provides spatial information with comprehensive content, clear images, and accurate positioning for highway planning. Combined with topographic maps, as well as the information such as the width and length of the highway to be constructed, remote sensing information can be used to estimate the quantities of earthwork, bridges, and tunnels, and learn the construction progress.
2. Application in Highway Network Operation and Maintenance
Strengthening disaster monitoring and road damage assessment of highways and related transportation facilities, detecting subtle changes in highways and surrounding environments in time, and carrying out daily management and disaster warning of highways, are of very pressing significance to ensuring the smooth flow of traffic arteries and "lifelines" and improving highway capacity. The operation and maintenance management of highway network mainly includes two aspects: daily operation and maintenance management of highways, and road disaster monitoring and damage assessment of transportation facilities. The specific applications include:
1) Production of an all-inclusive transportation map: Information such as land use, road network, traffic flow, intersections and trunk roads is obtained from high-resolution remote sensing images, which, combined with GIS and ground data collection, is described in an intuitive, vivid, and graphic manner.
2) Detection of highway network changes: High-resolution remote sensing images for specific areas are regularly obtained, and new highways and new transportation hubs are extracted in time through the analysis of changes in high-resolution remote sensing images at different time phases, in order to update the highway network.
3) Monitoring of pavement health: Hyperspectral resolution data or high spatial resolution data, combined with the ground means, is used to identify the difference in pavement spectral reflectivity under different health conditions, obtain subgrade structure, pavement cracks, deformations and other information, and analyze the application prospects and details of high-resolution remote sensing technology in China's transportation industry, in hope of giving full play to the application efficiency of domestic satellites, and promoting the industrialization of high-resolution remote sensing data in China's transportation sector.
3. Application in Highway Network Traffic Survey
Traffic jams and the resulting social problems such as traffic accidents and traffic environment pollutions are extremely serious. Highway network traffic survey means an analysis of the current traffic network, transportation infrastructure and traffic flow through remote sensing images and related ground traffic detection equipment. Remote sensing is able to obtain ground information efficiently and accurately. With the development of space science and technology, the comprehensive use of remote sensing technology to conduct highway network traffic surveys can greatly save manpower and material resources, and provide basic data for traffic management and planning. Specific applications include: 1) Traffic network and infrastructure survey: High-resolution remote sensing images are used to identify and extract current highway network status, highway network, vehicle ownership and composition, traffic signals, intersection types, intersection types, intersection coordinates, traffic signs and other information. 2) Traffic survey and analysis: High-resolution remote sensing image data is used to assess the traffic status of national and provincial highways as well as key expressway networks. Specifically, first, high-resolution remote sensing image data is used to extract information on traffic flow, traffic density and traffic speed on the highway network, assess the traffic status of an area or a specific section, and analyze the operating efficiency and investment rationality of the highway network. Second, remote sensing image data is used to distinguish different types of vehicles running on the highway network, such as heavy trucks, light trucks, buses and cars, and analyze the changes in freight transport in regional highway networks or key highway sections. The data can serve as an important reference for national economic indicators, and also provide decision-making support for local transportation investment and infrastructure construction. 3) Highway network traffic status assessment and change trend analysis: High-resolution remote sensing images, combined with other traffic detection equipment, are used to extract traffic information such as traffic flow, traffic density, traffic speed, and vehicle types, in order to assess the current traffic status and analyze its change trend.
4. Application in Monitoring and Assessment of Highway Environment
With the vigorous development of highway transportation and the rapid increase in the number of motor vehicles, the destruction of highway traffic to the environment, such as air pollution, vegetation damage, and soil erosion, has become extremely serious. High-resolution satellite remote sensing data not only includes geometrical structure and texture information of ground objects, but also contains accurate and detailed information on natural environment and ecological background. Therefore, it can be used to effectively monitor and assess the impact of the aforementioned environmental impact factors on highway surroundings. Specific applications include: 1) Monitoring of highway air pollution: The data obtained by the hyperspectral resolution atmospheric component detector equipped in the satellite is sued to calculate the composition of air around the highway, as a means of monitoring the air conditions around the highway and detecting whether the content of harmful gases exceeds the standard level. The actual measurements of pavement exhaust emission detectors are also used to estimate the daily emissions of highway vehicles, thereby assessing whether the highway will adversely affect the nature reserve environment and other environments. 2) Monitoring of highway vegetation destruction: Hyperspectral data or high spatial resolution data, combined with the ground means, is used to identify the difference in vegetation spectral reflectivity under different health conditions, obtain vegetation health status, and generate vegetation coverage products. 3) Monitoring of soil erosion: As the construction of expressways requires the excavation of a large amount of earth and stone, vegetation is damaged and a large amount of soil is exposed to the surface, leading to extremely vulnerable soil and water conservation systems around highways. High-resolution remote sensing images are used to regularly monitor exposed earth surfaces and typical landforms in the surrounding areas of highways. The digital elevation model (DEM) data is used to estimate the amount of soil erosion.
IV. Obstacles and Future Prospects of High-Resolution Data Industrialized Application in Transportation Industry
At present, various industries, including the transportation industry, have vigorously introduced information technologies such as remote sensing and GIS, in an effort to improve their internal and external informatization management level. However, compared to other industries such as agroforestry, meteorology, and surveying and mapping, the transportation industry is lagging behind in terms of the application of remote sensing, especially high-resolution remote sensing technology, and even the industrialization process. The reason behinds this includes not only application needs in the industry, but also the industry's own characteristics. To break the bottleneck that restricts the rapid development of remote sensing in the transportation industry, it is necessary to first understand the constraints, and then to discover and study the key links in the application of high-resolution remote sensing in the transportation industry, by taking into account the characteristics of high-resolution remote sensing as well as the information application in the transportation industry. Taking highways as an example, the following several key issues are present in the transportation industry: 1) Interpretation and identification of remote sensing characteristics in highway networks. The interpretation of remote sensing images for highway networks has advantages as well as disadvantages. Highways have a certain width, and their shape is similar to a strip line or a narrow rectangle. Highway networks are more or less regular with prominent and fixed geometric features, which is its advantage. One disadvantage is that it is difficult to accurately extract the width of highways and their surrounding facilities, and the other disadvantage is the randomness and zero-development of rural highways. This has created high requirements and new demands for remote sensing technologies such as image processing and pattern recognition. When extracting highway networks from high-resolution remote sensing images, especially high-resolution SAR images, higher resolution leads to richer detail features and more highway targets. Many narrow highways which are difficult to identify in low-resolution images can also be distinguished, but the non-target noise in the images is also increasing at the same time. Therefore, it is difficult to extract highway characteristics in high-resolution images. 2) Information integration of multi-source data. The transportation industry has been no longer satisfied with the development of informatization relying solely on remote sensing data sources. In practice, the industry can use highway surveillance cameras videos, floating cars, and fixed-point mounted sensors to monitor highway traffic flow and highway network disasters. Various sensors have been applied successively to obtain more and more large-area ground observation data of the same area. However, there is redundancy and complementarity in the data. How to integrate different kinds of sensor data organically and extract highway networks accurately and completely is a problem that needs to be resolved urgently and improved continuously. 3) Opportunities and challenges brought about by the reform of the large department system. The sound and rapid sustainable development of the transportation system is a strategic goal of China's transportation development in the new era. The reform of the large department system has brought about advances in the organizational structure of China's transportation administration system, but at the same time, aerial photography is required to count the facilities during the general survey of facilities. However, due to the missing of a large amount of basic transportation materials brought about by the reform of the large department system, the large amount of workload brought about by the reorganization of "lists," and the chaos of urban traffic management, there is an urgent need for efficient, rapid, and convenient information means to make up for the information gaps that have emerged in the industry reform of the large department system, in order to make up for missing information, optimize existing information, actively cooperate with national policies, and guide and support the smooth transition of the administrative and technical management of the transportation industry at all levels. 4) Governmental and civil affairs based on an all-inclusive transportation map. At present, China's surveying and mapping industry has launched surveying and mapping maps authorized by the state, such as the "Map World." However, the transportation industry, which has the closest tie with people, has no similar all-inclusive transportation map that integrates remote sensing resources and transportation resources. The development and application of such an all-inclusive transportation map is urgently demanded at both governmental and civil levels. Therefore, based on the full use of high-resolution remote sensing images and the integration of data from multiple sources, these resources are presented to different users in the form of layers and slices, which benefits the people and enhances people's well-being.