Brief introduction of remote sensing archaeological investigation and exploration

Remote sensing archaeology is to use the growth and distribution laws of ground vegetation, such as soil types, micro-landforms and other physical properties and the resulting differences in electromagnetic spectrum characteristics, and use cameras, video cameras, scanners, radars and other equipment to obtain information about electromagnetic wave data or images of ancient sites from different remote sensing platforms such as space shuttles and satellites, and then carry out optical or computer image processing on these information, so that the camera has appropriate contrast, obvious features and rich colors. Then the color, pattern, texture, temporal variation and spatial distribution of the image are identified and explained, so as to provide the location, shape, distribution and composition types of ancient remains and provide scientific information and data for archaeological discoveries.

The continuous development of remote sensing archaeology, as an advanced archaeological means with short period, high precision and no destruction of underground cultural relics, is gradually becoming an indispensable process in archaeological investigation, especially in the preliminary investigation of large-scale sites.

Since 1970s, people have obtained a great deal of remote sensing archaeological information through hundreds of satellites launched into outer space. For example, the pyramid archaeology in Egypt, the remote sensing study of the ancient city of Angkor in Cambodia, the exploration and investigation of the navigation culture of Phoenicians in Spain with spaceborne imaging radar, and so on.

These important archaeological discoveries have aroused people's enthusiasm for remote sensing archaeology.

Ancient sites, tombs, ancient buildings and cave temples are immovable cultural heritage. Important large-scale cultural remains, also known as large sites. The spatial geometry of a large mausoleum varies greatly, including the above-ground and underground parts. The above-ground area can reach dozens of square kilometers, and there are hundreds to tens of thousands of square meters of underground tombs. There are close archaeological and cultural ties between them.

Ancient sites and relics are places where people lived in the past, so it will inevitably lead to changes in their natural form at that time, making them different from the pure natural environment around them. Although these changes are not easy to detect after artificial disturbance, they are different from the original surrounding environment after all, and are preserved through the differences in surface water conditions, vegetation growth, land use and landform structure. These anomalies were recorded by remote sensing images, which provided the basis for archaeological interpretation and analysis. Remote sensing archaeology is to use these differences to obtain initial data, and then determine whether there are archaeological sites in a certain area.

As a branch of archaeology, modern remote sensing archaeology is mainly applied to the investigation of ancient large-scale sites, underground remains, underwater archaeology, environmental archaeology and urban remote sensing archaeology. Site investigation is the premise of archaeological work. Archaeologists can only dig when the site is discovered. However, the traditional field investigation method needs a lot of manpower and material resources, and the effect is often not obvious. Using remote sensing technology, people can investigate large-scale sites, which can not only save costs, but also help to grasp the sites from a macro perspective.

Large sites on the ground, due to the differences with the surrounding environment, are bound to be reflected in the pictures. At the same time, because remote sensing archaeology has strong penetrating power, it can detect underground sites well. The Mausoleum of the First Qin Dynasty in China has been explored by remote sensing technology for many times, thus making great contributions to the study of the Mausoleum of the First Qin Dynasty.

As a new archaeological technology, remote sensing archaeology also plays an important role in the application of underwater archaeology. Archaeologists use aerial remote sensing to detect underwater sites, in order to investigate the topography and features of the seabed before being submerged, determine the authenticity and location range of ancient sites on the seabed, and then speculate and study the development of paleogeography, paleoclimate and ancient society. These have made great achievements and promoted the research of cultural relics protection.

Because remote sensing archaeology is very different from traditional archaeology in survey methods and data processing, it has some incomparable advantages, mainly in the following aspects:

1. The macro survey of remote sensing archaeology has a wide field of vision.

Remote sensing archaeology is more cost-effective than traditional archaeology. Traditional archaeology mainly relies on manpower to investigate the site, and the field workload is very huge. However, people's energy and eyesight are very limited, and a small-scale on-the-spot investigation is still acceptable. If a large-scale population census is conducted in an area, it is difficult to see the whole picture. Especially for the investigation of special environment such as desert, grassland and ancient city ruins, due to the limitation of natural environment, field investigation is quite difficult, and it is even more difficult to get accurate investigation results. Remote sensing archaeology can overlook the ground in the air and photograph the topography of an area in an all-round way, without being limited by the geographical environment, which makes it possible to obtain local pictures clearly in many places where hiking is very difficult, thus greatly saving the cost of archaeological investigation.

Using remote sensors can clearly overlook the face of the earth from a height of hundreds of kilometers away, expanding the horizons of archaeologists. For example, the East Turkana region in Kenya is rich in early human fossils. In the space remote sensing image, the white sedimentary layer rich in human fossils presents a unique color (spectral characteristics), which rapidly expands the place where fossils are excavated.

2. Abundant archaeological information can be obtained.

Visible light, infrared, microwave, ultraviolet and multispectral remote sensing technologies of space remote sensing have been applied in archaeology. Remote sensing archaeology has the advantages of wide coverage, wide spectral range and high temporal and spatial resolution. Remote sensing images are easy to obtain the global information of an area, and the imaging scales of remote sensing images vary widely, which is beneficial for people to study the obtained images. The naked eye can only observe the reflected energy of electromagnetic waves in visible light, while remote sensing can observe all-band electromagnetic waves in the range of ultraviolet, visible light, infrared, thermal infrared, microwave and other energy waves to detect objects on the ground and underground. Due to the application of satellite technology, modern remote sensing archaeology can obtain remote sensing data of sites all the time. For example, an ancient castle in the north of London was destroyed by war when the Roman Empire collapsed, and was buried deep underground by barren soil. Space remote sensing images clearly show that the ability of plants here to reflect infrared rays has decreased, which makes the remains of this castle built in the era of Julius Caesar in Rome reappear. Another example is 1978, when the dense tropical rain forest in Guatemala was remotely sensed by microwave, a grid as dense as a spider's web was found on the enhanced remote sensing image. Through ground investigation, it is confirmed that this criss-crossing grid was originally an irrigation canal built by ancient Mayans, which provided valuable information for the study of Mayan civilization.

3. Conducive to the protection of cultural relics

Remote sensing archaeology does much less damage to ancient sites than traditional archaeology. Archaeological excavation itself is a kind of destruction of cultural relics, but many rescue excavations are imperative. Remote sensing archaeology is an effective method to change this passive situation. Using remote sensing images, we can understand the structure of sites and ancient tombs without destroying cultural relics, and minimize the damage. The powerful penetration of remote sensing technology makes it unnecessary to carry out large-scale excavation, which can save a lot of manpower and material resources and will not cause any damage to the site. As an ancient civilization with a history of 5,000 years, China has a large number of sites to be proved. Using remote sensing archaeological technology, we can not only find out various large-scale ancient settlements and ancient cities, but also protect them as much as possible.

4. Remote sensing archaeology should be combined with traditional archaeology to learn from each other.

"Remote Sensing Archaeology" is a science and technology as well as a research method. Although remote sensing archaeology can greatly reduce the workload of field archaeology, it can never replace field archaeology. It cannot solve the basic archaeological problems such as the age of the site and the study of unearthed objects, so remote sensing archaeology must be closely combined with field archaeology. Only in this way can archaeological work get twice the result with half the effort.

The application of remote sensing archaeology technology in China is late, but it develops rapidly. In the archaeological investigation of many sites in China, remote sensing archaeological technology has played an important role. For example, when Sanmenxia Reservoir was built in 1960s, archaeologists in China used aerial photographs to analyze the distribution of ancient sites and tombs in the reservoir area. In 1970s, remote sensing technology was used to detect the mausoleum of the First Qin Emperor. Since 1990s, China has increased its investment in remote sensing archaeology, established a number of key laboratories, and held some international conferences to conduct special academic research on remote sensing archaeology.

In recent years, scientific and technological archaeologists have discovered the Ming Dynasty shipwreck in the Pearl River Estuary by using satellite remote sensing technology, and successfully salvaged the water. Then the underwater shipwrecks were investigated in Bohai Bay, Yellow Sea and East China Sea, and more than 500 shipwrecks in different historical periods were found in the Yangtze River estuary alone.

China scientific and technological archaeologists also used color infrared aerial photographs to reveal the present situation of the Great Wall in Beijing, the plane shape of the foundation of the ancient buildings in Yuanmingyuan, and the trend of the outer wall of Tokyo in the Northern Song Dynasty in Henan Province, and to understand the ecological and environmental reasons why Pan Geng, the king of Yin, moved his capital to Anyang, Henan Province 3,500 years ago. In remote sensing archaeology of Yin Ruins in Anyang, Henan, China Academy of Social Sciences used computer image processing technology to combine TM images with stable aerial images, which greatly improved the quality of remote sensing images and discovered some new Yin Ruins and tombs.

In addition, scientific and technological archaeologists discovered the ancient mulberry garden in the center of Taklimakan desert by using advanced remote sensing technology; Found the ancient "Guo Jing" site that disappeared in the desert hinterland for nearly 2000 years; The Grand Canal excavated in Yang Di was discovered, which has been silted for over 1000 years.

China's remote sensing archaeology attaches importance to multidisciplinary joint research. Natural science and social science workers learn from each other and give full play to their respective professional expertise.

Large-scale archaeological investigation should make comprehensive use of space remote sensing information, such as aerial photography, satellite photos, multi-spectral satellite remote sensing images and airborne radar images. , to carry out nondestructive testing and identification of archaeological sites on the ground. At the same time, combined with geophysical prospecting technology and conventional field archaeological means, archaeological sites are explored and discovered, and archaeological surveying and mapping, cultural relics protection and archaeological research are carried out.

Archaeologists believe that using the new scientific method of remote sensing archaeology, we will find more secrets and treasures that amaze the world in this ancient and vast land of China. It is more conducive to the protection and discovery of cultural relics.