In this blog post, we’ll examine the concept, history, operating principles, and types of remote exploration through scenes from the movie ‘WALL-E’, and explore how current and future remote exploration technologies can be utilized.
Introduction
In a future set 700 years from now, humanity has left a desolate Earth behind, entrusting a remarkable robot with the mission of cleaning up the planet. WALL·E, who roams the landscape collecting and compacting trash, falls in love with EVE, a robot who arrives on Earth to carry out a different mission. This is the main plot of the 2008 sci-fi animated film ‘WALL·E’. EVE, who came to Earth to find WALL·E, is tasked with exploring the planet to determine whether humans can live there again by checking for the presence of plants. EVE scans the Earth’s environment, discovers plants, and uses this as a crucial clue to assess whether the environment is habitable for humans. In this way, using sensors to assess the condition or characteristics of an object without direct contact can be viewed as a conceptual example of remote sensing.
Remote sensing is of great significance because it can be widely applied not only to future generations but also to our daily lives today, extending all the way to space exploration. For example, we can detect abnormalities inside the body through X-rays and obtain high-resolution images of the Earth’s surface more easily and efficiently via satellites. South Korea is also acquiring high-resolution Earth observation imagery through satellites such as the Arirang satellites, and this satellite imagery is being utilized in various fields, including land management, disaster monitoring, marine and water resource management, agriculture and forestry, and environmental and meteorological observations. Although the utility of remote sensing is increasing, the technology remains somewhat unfamiliar to the general public. To promote better utilization of remote sensing and ensure the effective future development of South Korea’s remote sensing technology, we will take a detailed look at the history, operating principles, and types of remote sensing.
What Is Remote Sensing?
Remote sensing refers to the activity of detecting or investigating the physical and chemical characteristics of a target from a distance without direct contact. Therefore, it can be broadly defined as encompassing a wide range of technologies, from taking general photographs from aircraft or satellites to measuring the location, size, and condition of objects. In other words, Eve using sensors to detect the presence of plants without making direct contact with the ground can be viewed as an application that illustrates the concept of remote sensing.
The development of remote sensing originated from the need to assess conditions in distant locations, a need that was particularly prominent during wartime. The evolution of remote sensing technology is closely linked to the development of aerial photography and military reconnaissance technology. The term “remote sensing” was first used in the 1950s by the U.S. Naval Research Laboratory; at that time, it was used as a broad concept encompassing aerial photogrammetry and surveying using newly developed sensors.
In the early days, aerial photography was primarily driven by curiosity, but from the 1920s through the period leading up to World War II, its scope expanded into civilian sectors such as geological surveys, vegetation surveys, cartography, and crop surveys. Later, as its military value became apparent—particularly during World War II—related technologies advanced significantly in countries such as the United Kingdom and Germany, where infrared technology and radar (RADAR, Radio Detection and Ranging) were utilized to identify enemy military facilities and assess damage.
In addition, remote sensing has traditionally been used for preliminary surveys and large-scale exploration of energy resources, urban planning, and military operations. As such, the applications of remote sensing are diverse. It can be particularly valuable as a key technology in energy resource exploration. For example, using portable remote sensing equipment, it is relatively easy to distinguish between gold and pyrite in the field, even though they appear similar in color and luster.
Future-generation remote sensing is expected to play a major role in ushering in the era of space exploration, as depicted in ‘WALL-E’. Moving beyond traditional military and industrial purposes, it will be utilized in lunar and planetary exploration, helping to advance future space exploration technologies. As is a frequent theme in movies, if we seek to find planets beyond Earth where humans can live, remote sensing technology can play a crucial role. This is because by sending sensors to celestial bodies or regions that are difficult for humans to access directly, or by collecting information using satellites, we can understand the characteristics of areas that are otherwise hard to explore firsthand.
Even if it cannot be distinguished with the naked eye, it is possible with remote sensing
So, what is the operating principle behind remote sensing, which has such diverse applications? The Sun, the primary energy source for optical remote sensing, emits electromagnetic wave energy that reaches Earth. When electromagnetic energy strikes the Earth’s surface, objects on Earth absorb or reflect it depending on their type—a phenomenon known as the object’s intrinsic spectral characteristics. The basic principle of remote sensing technology involves measuring the energy reflected, scattered, or emitted by the target and analyzing the object’s spectral characteristics.
Remote sensing can measure not only the visible light spectrum—which is visible to the human eye—but also ultraviolet (UV) and infrared (IR) radiation beyond the visible spectrum, as well as microwave radiation with even longer wavelengths. Because of these characteristics, data can be acquired across a broad range of wavelengths that are difficult for humans to perceive directly, offering the advantage of being able to analyze the characteristics of a target based on this diverse wavelength information.
Furthermore, applying remote sensing techniques to the compositional analysis of geological media overcomes the limitations of traditional compositional analysis methods in terms of time efficiency, field applicability, and non-destructive evaluation. New methodologies are being developed to enable real-time or near-real-time analysis, thereby reducing the time required for analysis; another advantage is the ability to perform analyses directly in the field that were previously conducted in laboratories. Furthermore, the ability to analyze geological media without destroying them and while preserving the site is another advantage of remote sensing. This is easy to understand if you consider the scene in the movie where Eve surveys the surface of an area on the spot in a short amount of time without causing any direct damage to the surveyed area.
What kind of remote sensing did Eve use?
Remote sensing can be classified in various ways depending on the sensors, energy sources, and observation methods used. In this article, we will examine the main categories: optical satellite remote sensing, optical aerial remote sensing, and active remote sensing. First is optical satellite remote sensing. Optical satellite remote sensing measures and records the intensity of electromagnetic waves—emitted from external energy sources such as sunlight—that are reflected or scattered off a target surface using sensors mounted on a satellite. Generally, satellites intended for Earth observation or weather satellites used for meteorological observation fall into this category.
Optical satellite remote sensing does not explore all wavelength ranges of electromagnetic waves equally. Energy emitted by the Sun first passes through the Earth’s atmosphere, is then reflected or scattered by the Earth’s surface, and subsequently passes through the atmosphere again before being detected by sensors aboard the satellite.
As electromagnetic energy passes through the Earth’s atmosphere, certain wavelength ranges are absorbed by the gases and water vapor that make up the atmosphere. For this reason, observations are focused on wavelength ranges where the characteristics of the target on the Earth’s surface can be transmitted to the sensors with relatively less absorption by the atmosphere. In optical satellite remote sensing, the wavelength range from visible light to infrared is generally the primary range used.
Second is optical aerial remote sensing. Optical aerial remote sensing is a form of remote sensing that uses aircraft; it has the advantage of allowing data to be acquired at the desired time more easily than when using satellites. However, from a cost perspective, while the initial entry costs for the aircraft-based method may be relatively lower compared to the initial costs required to launch and operate a satellite, it can be less efficient than satellites for continuous data acquisition in the long term because an aircraft must be operated for each measurement. Additionally, there is the disadvantage that the survey area may be limited because surveys are conducted at relatively lower altitudes than satellites and considerations regarding international territorial boundaries are necessary. Optical aerial remote sensing may utilize wavelength ranges similar to or identical to those used in satellite-based optical remote sensing.
Finally, there is active remote sensing. Active remote sensing does not passively measure natural electromagnetic energy, such as sunlight; rather, it involves a sensor directly emitting electromagnetic energy at a specific wavelength for the survey and measuring the energy reflected back from the target. Because it uses an artificial source of electromagnetic energy, it has the advantage of enabling exploration even at night when there is no sunlight. Considering the film’s setting, Eve’s exploration method can also be interpreted as aligning with the characteristics of active remote sensing. However, it cannot be definitively concluded that Eve’s specific sensors and exploration principles in the film are identical to those of actual remote sensing equipment. Since Eve is a robot designed to detect the presence of plants, it is reasonable to assume that it used sensors capable of detecting plant characteristics. For example, it is possible that it detected specific wavelength ranges capable of distinguishing the spectral characteristics of plants and used this information to determine their presence. In this way, utilizing electromagnetic waves in specific wavelength ranges tailored to the characteristics of the target object allows for a more effective assessment of the target’s properties.
A prime example of active remote sensing is LiDAR (Light Detection and Ranging), a technology that uses lasers to measure distance. To determine the location and shape of terrain and objects on the ground, the sensor emits a laser beam and calculates the distance by measuring the signal that returns from the target. LiDAR is used not only for creating topographic maps but also for investigating the form and characteristics of land cover, as well as for determining the structure of vegetation and atmospheric composition. In this way, active remote sensing allows us to obtain a variety of information by having the sensor directly emit energy, measure the signal that returns after the energy interacts with the target, and analyze that data.
In Conclusion
Satellite imagery now allows us to see small villages in countries we have never visited, and we can use satellite observation data to obtain the information needed to predict weather and changes in the Earth’s environment in the near future. Whereas people in the past primarily lived by observing their immediate surroundings, today we can understand the appearance and changes occurring in every corner of the Earth—even places we have never visited—through remote sensing technology. In this way, remote sensing serves as a guide, revealing places we have never been to and paths we do not know.
As remote sensing technology continues to advance, it can also play a crucial role in enabling humanity to venture into space. By sending remote sensing technology first to places that are difficult for humans to reach directly or by observing them from a distance, we can gather a variety of information, which helps us understand new frontiers. Just as scientists in the movie ‘Eve’ sent “Eve” to Earth to discover the future of humanity, remote sensing will become a vital technology that brings us one step closer to unknown realms that humans cannot reach on their own.
