Remote sensing drones: "Elf" is a big use

In recent years, unmanned aerial vehicle (UAV) platforms equipped with mission payloads such as camera equipment, controlled by pilots or autonomously controlled by flight control systems have played an increasingly important role in remote sensing applications such as surveying and mapping, disaster reduction and emergency response, and become a new member of the remote sensing family. UAV is known as the "elf" of remote sensing family because of its small mobility, low altitude flight, high spatial and temporal resolution, diverse and flexible load configuration and other characteristics. However, this "elf" has a great use! Unmanned Aerial Vehicle (UAV) is commonly referred to as an Unmanned aerial vehicle (UAV). Generally, it refers to an air vehicle driven by power and not carrying an operator, which uses aerodynamic force to provide the required lift for the aircraft, can fly autonomically or remotely, can be used once and can be recycled, and can carry lethal or non-lethal mission payloads, such as taking photos, broadcasting drugs, playing sound, etc.

Drones are not a new thing, they have been developed for centuries. In 1917, the Royal Aeronautical Institute of the United Kingdom initially combined aerodynamics, lightweight engines and radio to develop the world's first unmanned aircraft. In December of the same year, American inventor Elmer Spee completed the first flight of the "aerial torpedo" using a gyroscope he invented and a radio control system developed by the Western Electric Company of the United States. In the beginning, drones were mainly used in the military field. After entering the 21st century, with the rapid development of modern electronics, precision machinery, navigation and positioning and remote sensing and other related technologies, the application of unmanned aerial vehicles in the civilian field is more and more extensive, and the formation of an industry.

The UAV can be classified according to the use function, aerodynamic layout, power type, size and weight, flight speed, activity radius, flight height and other methods. According to the function of use, drones can be divided into military drones, civilian drones and consumer drones. Military UAVs can be divided into reconnaissance UAVs, electronic countermeasures UAVs, communication relay UAVs, attack UAVs and unmanned target UAVs. Civil UAVs can be divided into various purposes of inspection, surveillance, mapping and detection UAVs and agricultural UAVs; Consumer drones are mainly used for leisure purposes such as personal aerial photography and gaming.

According to the aerodynamic layout, UAVs can be divided into fixed-wing UAVs, rotary-wing UAVs, flapping UAVs and compound layout. Fixed-wing UAVs rely on the power device to generate forward thrust or pull when flying, and the main airfoil to generate lift is fixed and unchanged relative to the fuselage, mainly in the form of conventional layout, duck layout, tailless or flying wing layout, three airfoil, etc. The lift rotor blades of rotorcraft are rotating relative to the fuselage during flight, and can be divided into unmanned helicopters, multi-rotor drones and unmanned rotorcraft. The first two forms of UAV rotorcraft are directly driven by the power device and can take off and land vertically and hover, while the rotorcraft of unmanned rotorcraft is unpowered. Ornithopterus UAV relies on the wings to flutter up and down like the wings of birds to obtain lift and power, which is suitable for small and miniature UAV; Composite layout UAVs consist of a combination of basic types, mainly including tilt-rotor UAVs and rotary/fixed wing UAVs.

According to the power type, UAVs are mainly divided into two types: oil-powered UAVs and electric-powered UAVs, and in recent years, UAVs with solar energy and hydrogen fuel cells as the core power have been continuously developed.

According to size and weight, drones can be divided into micro drones, light small drones, small drones, medium drones and large drones. Microdrones generally weigh less than 1 kilogram and are less than 15 centimeters in size. The weight of light and small drones is generally between 1 and 7 kg, the weight of small drones is generally between 1 and 200 kg, and the weight of medium-sized drones is generally 200 to 500 kg.

Now, drones have become a lot of children, big friends of the toy "new favorite" - consumer drones generally use low-cost multi-rotor platform, mainly for aerial photography, games and other leisure purposes. The domestic consumer drone market erupted around 2012. Before this, drones were mainly used in the industrial field, and the consumer market was mainly some model aircraft enthusiasts and enthusiasts. At present, the development of China's UAV industry shows a "blowout" trend, in addition to aviation, aerospace related scientific research institutions and universities, many private enterprises have joined the ranks of research and development, civilian UAV research and development and application can be described as in full swing, China's UAV application in consumer entertainment and other fields has been in the forefront of the world.

The rapidly developing UAV has become an emerging remote sensing platform, which is widely used in the fields of land aerial survey, agriculture, forestry and plant protection, atmospheric detection, disaster relief, national defense and security after being equipped with various remote sensing devices.

UAV remote sensing has ultra-high resolution and high frequency acquisition capabilities, which can complement satellite remote sensing capabilities. Compared with man-machine remote sensing, it has higher cost performance and maneuverability. The real-time observation capability of UAV remote sensing is difficult to achieve on the current satellite remote sensing observation platform. Satellite remote sensing can provide sub-meter level images, but the higher the resolution, the larger the satellite revisit period. UAV images can easily provide ground information with a resolution of centimeters or even higher, and there is no contradiction between high spatial resolution and time resolution, and the dialectical unity of space and time is realized on the basis of low cost. It can be said that the emergence and rapid development of UAV remote sensing has made remote sensing science research a big step forward from macro to micro. Compared with the high cost and centralized management of satellite platforms, the UAV platform allows the acquisition of remote sensing data to enter the era of popularization, and truly realizes the remote sensing application of to C (user).

Due to the unique advantages of UAV remote sensing, many areas where the application effect of satellite data is not good or cannot be realized in the past can be well implemented by UAV remote sensing. For example, the use of UAV hyperspectral remote sensing can classify and identify surface species, discover and identify alien species invasion through UAV hyperspectral data, and provide data support for ecological environmental protection. For another example, UAV remote sensing has provided convenient conditions for extreme environment sampling and data acquisition, providing first-hand data for many studies and contributing to a number of new scientific discoveries. Since 2010, NASA has helped build a fine-structure system for typhoons after successfully monitoring the paths of five Atlantic hurricanes using the high-altitude, long-endurance unmanned aerial vehicle GlobalHawk. In 2017, a multinational team of researchers used drones equipped with cameras and other sensors to film the eruption of a volcano in Tierra del Fuego, Guatemala, to measure the data and model the dynamic process.

It is particularly worth saying that UAV remote sensing has played a key role in disaster remote sensing monitoring. In recent years, drones can be seen in major natural disaster emergency events: in 2008 Wenchuan earthquake rescue, drone remote sensing technology was put into use; Later major natural disasters, such as the Sichuan Maoxian landslide, the Dalian oil spill incident, the Tianjin port major hazardous chemical explosion accident and other emergency relief, drones have played an important role.

In the field of industry application, drone inspection of oil and gas, power transmission, and photovoltaic power plant infrastructure has been normalized. In some government departments, drones are gradually being incorporated into the business system, such as environmental protection departments using drones to carry out river sewage discharge inspection and rectification. The high-frequency, responsive drone platform and centimeter-level drone images strongly support the daily operation of routine operations of environmental protection related business units.

Due to convenience and flexibility, high public participation, drone innovation is also very active and developing rapidly. The deep combination of UAV remote sensing and other related technical fields has shown a large number of expansive applications, which is called the "remote sensing +" application of UAV. For example, in the real-time transmission of "remote sensing + data", UAV remote sensing is very important for military, emergency disaster reduction and rescue, and many homeland security monitoring and disaster relief operations rely on UAV remote sensing and real-time transmission to provide timely information for decision-making.

In terms of "remote sensing + real-time positioning and map construction technology (SLAM)", the combination of UAV and SLAM enhances the navigation and obstacle avoidance of UAV, and has important application prospects in the intelligent data acquisition and autonomous flight of UAV.

In terms of "remote sensing + decision-making and execution technology", the integration of "UAV remote sensing + identification + task planning + task execution" has been achieved. For example, drone remote sensing can realize remote sensing monitoring of field agricultural conditions, form a prescription map of diseases and pests, plan reasonable routes, perform precise pesticide spraying, and integrate static remote sensing observation with real-time decision-making and implementation.

In terms of "remote sensing + low-altitude route planning", the current diversified application needs of UAVs are mainly at low altitude. Most of the "low, slow and small" UAVs are concentrated in the near-ground airspace below 500 meters, and the surface changes of this airspace are diverse, the situation is complex, and the flight safety and efficiency problems are prominent. Therefore, the low-altitude air routes, especially the low-altitude public air routes of UAVs in urbanization areas, are more important. Meticulous planning is required. The efficiency of data acquisition through traditional statistical channels is low, and the use of high-resolution and dynamic UAV remote sensing data in urban areas to serve the construction of low-altitude route planning has become a research frontier, and China has taken the lead in actively exploring in this aspect.

In terms of "remote sensing + regional networking", although the remote sensing capability of UAV is very strong and the spatial resolution is high, the coverage area is small, and it is difficult to meet the demand for UAV remote sensing in large regional applications. For example, through a certain organizational model and technical system, the national distributed UAV remote sensing resources are planned and deployed to build a large-area, high-frequency, fast-response centimeter resolution and remote sensing monitoring system, so as to complete a large-area measurement task. In general, the application and development of UAV has formed a trend of application in the whole field, and with the strong traction of application demand and the strong support of new technology development, the development of UAV is expected in the future.