What Does an Imaging Technologist Do?

Thermal imaging technology refers to the use of an infrared detector and an optical imaging objective lens to receive the infrared radiation energy distribution pattern of the measured target and reflect it on the photosensitive element of the infrared detector to obtain an infrared thermal image. This thermal image is related to the heat of the surface of the object. The distribution field corresponds. In popular terms, an infrared thermal imager is to convert invisible infrared energy emitted by an object into a visible thermal image. Different colors on the thermal image represent different temperatures of the measured object.

Thermal imaging technology

In 1800, British astronomer Mr. William Herschel used a prism to split the sunlight into monochromatic light from red to purple, and measured the thermal effects of different colors of light in turn. He found that when the mercury thermometer moved beyond the red light boundary and the human eye could not see any dark areas of light, the temperature was higher than the red light area. Repeated tests have shown that there is indeed a "hot line" that is invisible to the human eye outside the red light, which was later called "infrared", that is, "infrared radiation".

Infrared rays are commonly found in nature. Any object whose temperature is above absolute zero (-273.16 ° C) will emit infrared rays, such as ice cubes.

Light is visible light, which is an electromagnetic wave that the human eye can feel. The wavelength of visible light is: 0.38-0.78 microns. Electromagnetic waves shorter than 0.38 microns and electromagnetic waves longer than 0.78 microns cannot be perceived by the human eye. Electromagnetic waves shorter than 0.38 micrometers are outside the visible light spectrum and are called ultraviolet rays, and electromagnetic waves longer than 0.78 micrometers are outside the visible light spectrum and are called infrared rays. Infrared, also called infrared radiation, refers to electromagnetic waves with a wavelength of 0.78 to 1000 microns. The part with a wavelength of 0.78 to 2.0 microns is called near infrared, and the part with a wavelength of 2.0 to 1000 microns is called thermal infrared. Cameras get photos, TV cameras get TV images, all are visible light imaging. In nature, all objects can radiate infrared rays. Therefore, a detector is used to measure the infrared difference between the target itself and the background, and different infrared images can be obtained. The image formed by thermal infrared is called a heat map. The thermal image of the target is different from the visible light image of the target. It is not the visible image of the target that can be seen by the human eye, but an image of the surface temperature distribution of the target. In other words, infrared thermal imaging prevents the human eye from directly seeing the surface temperature of the target. The distribution becomes a thermal image representing the target surface temperature distribution that can be seen by the human eye.

Since the Second World War, thermal imaging technology has been applied to the military. Because this instrument works by heat radiation, it can let soldiers clearly see the enemy's whereabouts through the dark battlefield. And because it is a passive receiving system, it is more secure and hidden than visible light devices such as radio radars.

Nowadays, thermal imaging technology has been widely used in daily life. An important application is the diagnosis of diseases. Everyone knows that when inflammation occurs in a certain part of the body, the body temperature will rise. Measuring the body temperature can determine whether there is inflammation, but the specific location of the inflammation cannot be determined. The thermal imaging camera can directly give the temperature of the human body. The field distribution map, comparing the heat map of the lesion with the normal heat map, can diagnose the lesion site from abnormal changes. Thermal imaging technology can also be used in the operating room. When blood flows through the newly placed arterial blood vessel, the color of the arterial tube on the thermal imager changes from gray to white. Under normal circumstances, it is difficult for the naked eye to observe whether the blood vessel is unobstructed.

Similar to the diagnosis of diseases, electrical components, train axle boxes, circuit boards, etc. of high-voltage transmission and transformation have failed. You can also use a thermal imager to directly observe and check to avoid losses caused by the failure. Thermal imaging cameras can also be used for geological surveys, geothermal surveys, forest vegetation distribution, atmospheric and ocean monitoring, fire detection and rescue. Thermal imaging cameras can help rescuers find victims who have been concealed by smoke and darkness, and rescue them.

Thermal imaging can also help scientists further explore the mysteries of the universe. It can be expected that the application fields of thermal imaging technology will be more fully developed, promoted and popularized in the future.

China's thermal imaging technology started in the mid-1970s. After more than 20 years of unremitting efforts and relying on our own technical strength, Chinese engineers have successfully developed a variety of thermal imaging cameras and thermal imaging systems. Infrared thermal imaging cameras with excellent performance are being widely used in China's national defense and national economic construction.

Texas Instruments Corporation (TI) developed the first generation of thermal infrared imaging device, called infrared forward-looking system, for the first time in 1964. This type of device uses optical element movement machinery to perform image decomposition scanning of the target's thermal radiation. Photoelectric detectors are then used for light-electric conversion, and finally video image signals are formed and displayed on the screen. The infrared forward-looking system is still an important device on military aircraft, ships and tanks. In the mid-1960s, a thermal infrared imaging device with a temperature measurement function was developed on the basis of the infrared forward-looking device. This second-generation infrared imaging device is commonly referred to as a thermal imager.

In the 1970s, infrared heat television products were developed that did not require cooling. In the 1990s, refrigerated and non-refrigerated focal plane infrared thermal imaging products appeared. This is the latest generation of infrared television products, which can be used for large-scale industrial production and improve the application of infrared thermal imaging to a new stage.

In the 1970s, Chinese organizations have begun to study infrared thermal imaging technology. By the early 1980s, China had made certain progress in the development and production of long-wave infrared components. By the end of the 1980s and early 1990s, China had successfully developed a real-time infrared imaging prototype with high sensitivity and temperature resolution.

In the 1990s, China has developed key technologies such as low-noise wide-band preamplifiers and miniature refrigerators on infrared imaging equipment. From experimental to application, it is mainly used for troops, such as portable field thermal cameras. , Anti-tank missiles, anti-aircraft radars, tanks, warship artillery, etc. In terms of infrared thermal imaging technology, China has invested a lot of manpower and material resources, and formed a considerable scale of research and development capabilities. However, in general, it is far from the world's advanced level, and it is about 10 years behind the West. At present foreign countries have begun to equip troops with second-generation infrared thermal imagers and have started the third-generation research and development work, but China has only now promoted the first-generation infrared imagers. Internationally, the United States, France, and Israel are pioneers in this regard, and other countries, including Russia, are at the downstream level. In recent years, China's infrared imaging technology has developed by leaps and bounds, and the gap with the West is gradually narrowing. The advanced nature of some equipment can also be synchronized with the West. It is believed that the gap between China and the West will further narrow, especially in the application of new technologies. It can be unique. Infrared thermal imaging products can be divided into two types: refrigerated and non-refrigerated. At present, the most advanced infrared thermal imager has a temperature sensitivity of 0.03 degrees Celsius. No matter day or night, it can be used to detect the enemy in the jungle with an infrared instrument. The distance can be up to 100 meters. As a border anti-smuggling, it can also track the smuggling of flying seas. The distance can reach several kilometers. The thermal imager can not only observe the target in real time, but also perform dynamic analysis through the "thermal trace" of its track, because the thermal divergence of general objects has a certain time, and the thermal divergence of some objects takes a long time. For example, the cooking smoke ignited by the army and the vehicles that have been launched can leave "heat traces". The first generation of thermal imaging cameras mainly consisted of optical instruments with scanning devices, electronic amplification circuits, displays and other components. They have successfully equipped the army and made important contributions to ground observation, aerial reconnaissance, and surface insurance at night. The second-generation thermal imager mainly uses focal plane array technology, integrates tens of thousands or even hundreds of thousands of signal amplifiers, and places the chip on the focal plane of the optical system to obtain a panoramic image of the target without the need for light-machine scanning systems. The sensitivity and thermal resolution are greatly improved, and the detection distance and recognition ability of the target can be further improved.

The U.S. Supreme Court has established a new boundary in thermal imaging technology in houses, deciding that this is a search under the Fourth Amendment. One day in January 1992, federal agents suspected that Danny Kyllo was planting a cannabis plant in his home, so he used a thermal imager to measure heat radiation in Kyllo's house. The thermal imager detects the presence of thermal radiation. Almost all targets have thermal radiation emitted and exist between the scattered temperature values. Federal agents fixed the thermal imager across the street from Danny Kyllo's house, away from the surrounding area. Thermal imaging results showed that the roof and side walls were hotter than other parts of the house and warmer than those of its neighbors. Holding these detection results and other relevant information, federal agents believed that Danny Kyllo did use halides to grow marijuana, so he applied for and obtained a search warrant.

During a subsequent search of Kyllo, detectives found nearly a hundred cannabis plants growing inside the suspect's house. Kyllo was sued for marijuana production in violation of Title21U.SC§841 (a) (1). Kyllo filed an application for exclusion of evidence before the trial. The application was rejected by the court. In the ninth year after the heat can be measured, the Federal Supreme Court finally agreed to detect whether the heat emitted from homes was a reasonable search within the meaning of the Fourth Amendment.

Some provisions in the Fourth Amendment stipulate that people have the right to be protected in their homes from unreasonable searches. It was not until 1967 in the Katzv. UnitedStates case that the Supreme Court first formulated the principle that the "fourth Search under the Amendment. Since the Katz case, the Supreme Court has given guidance on what constitutes a reasonable expectation of privacy. In the case of houses, this concerns the range of heights (400 to 1,000 feet) that reasonable privacy expectations can reach and the end point it reaches horizontally (stopping in the area immediately adjacent to the house with fences). The fact of the Katz case raises a unique question in this context. The heat emitted from the house is measured outside the area directly adjacent to the house, but the heat itself is generated inside the house. From the perspective of the Supreme Court, it is clear that Kyllo has privacy expectations for his house, and society has always recognized that a person's home is the most important area for him to have reasonable privacy expectations. However, since the Katz case, the Supreme Court also stated that anything exposed to the public or law enforcement officers who are lawfully present will lose the Fourth Amendment even if it is in an area where reasonable privacy expectations exist. Protection of it (based on direct visual rules).

On June 11, 2001, the Federal Supreme Court ruled that thermal imaging constituted a violation of the Fourth Amendment by a five-to-four near-balance decision (very unusual combination of Justices Kurt, Thomas, Kingsberg and Blaye joined the same camp for judicial opinions). In this judicial decision, the judge concluded that the use of instruments not used by the general public to explore things in the home, and to understand the details of things in the house that could only be known through physical intrusion in the past, violated this practice. The reason that people's reasonable privacy expectations belong to an unreasonable search within the meaning of the Fourth Amendment.

What does this mean for law enforcement? Obviously this means that law enforcement officers cannot use thermal imaging cameras to measure the heat emitted from the house. More importantly, the Supreme Court's opinion seems to imply that any action by a law enforcement officer to use an instrument other than those used by the general public to invade an area (house) with a high level of reasonable privacy expectations may raise the " Tricky issues on the Fourth Amendment. In judicial opinion, the Supreme Court reiterated that the "Fourth Amendment" draws a firm line at the entrance to the house, and whether law enforcement officials walk into the room or measure the heat emitted from the house or implement any other method All intrusive surveillance must obtain a writ based on reasonable possibilities. With the rapid advancement of surveillance technology in recent years, it is natural to doubt that the Supreme Court will handle more such cases in the future, especially in areas involving reasonable expectations of privacy.