A New View from the Sky
Humanity has been observing our planet from space since the launch of Sputnik in 1957. Until now, however, this observation has been almost entirely limited to the Earth’s surface. The depths of the oceans, beneath the polar ice caps, terrain hidden by dense vegetation, and especially the earth’s crust beneath our feet have remained largely closed to the curious gaze from space.
China’s latest move is radically changing this boundary. The newly launched next-generation satellite has made history as one of the first operational systems capable of imaging the inside of the earth’s crust from orbit by combining synthetic aperture radar (SAR) technology with low-frequency electromagnetic wave analysis. This satellite, reported to have been developed under the “Ludi Tanshi” (Land Exploration) program, can simultaneously use P-band and L-band frequencies to collect data at different depth and resolution levels.
Technical Infrastructure and Working Principles
The Evolution of Synthetic Aperture Radar
Synthetic aperture radar (SAR) is an imaging technique that processes radar echoes collected by a moving antenna to achieve the resolution that a physically much larger antenna would provide. Traditional SAR systems generally operate in X-band (8-12 GHz), C-band (4-8 GHz) or S-band (2-4 GHz) frequencies and show extraordinary success in surface imaging. However, these high-frequency signals are extremely limited in their ability to penetrate soil and rock.
China’s new satellite breaks through this frequency barrier by using a system that can operate in P-band (approximately 300 MHz to 1 GHz) and partially in VHF bands. Low-frequency electromagnetic waves, thanks to their longer wavelengths, can penetrate materials such as soil, sand, rock and even concrete. Although penetration depth varies depending on the conductivity and dielectric properties of the material, it can be between 100 and 500 meters under ideal conditions (in low-conductivity environments such as dry sand and limestone).
Dual-Band Hybrid System
One of the satellite’s most critical technical features is its ability to operate P-band and L-band (1-2 GHz) radars simultaneously. This dual-band architecture allows targets at different depths and of different scales to be detected at the same time. P-band radar provides deeper penetration (100-500m) but has relatively low resolution; it is used for detecting large-scale geological structures, deep bunkers and fault lines. L-band radar, on the other hand, offers shallower penetration (20-50m) but much higher resolution; it is effective in detailed mapping of near-surface tunnels, pipelines, archaeological remains and military fortifications. The interferometric combination of these two data streams (InSAR technique) enables the creation of three-dimensional models of underground structures.
Phase Change Analysis and Dielectric Contrast
The basic physical principle of underground imaging is the reflection of electromagnetic waves at the boundaries between media with different dielectric properties. The dielectric difference between the concrete wall of an underground bunker and the surrounding soil causes part of the radar signal to be reflected back. The Chinese satellite is equipped with receivers sensitive enough to detect these extremely weak reflections.
One of the innovative aspects of the system is phase change analysis. A signal reflected from an underground cavity or a structure of different density shows a phase difference compared to signals coming from its surroundings. These phase differences are measured at the millisecond level to obtain information about the location, size and even shape of underground anomalies. Signal processing algorithms developed by the China Electronics Technology Group Corporation (CETC) combine this phase data with AI-supported analysis to minimize false positives and increase detection accuracy.
Orbit and Satellite Constellation Architecture
The satellite is deployed in a sun-synchronous orbit (SSO) at an altitude of approximately 500-600 km. This orbital choice provides the advantage of imaging the same region under similar illumination conditions on each pass and facilitates change detection. Furthermore, rather than a single satellite, a constellation architecture consisting of three or four satellites is planned. In this way, the revisit time for the same region will be reduced to under 24 hours, tomographic underground maps will be created through multi-angle imaging, and the total capacity and global coverage area of the system will be increased.
Comparative Technical Superiority
To understand China’s position in this field, a comparison with existing systems is necessary. China’s Ludi Tanshi system uses P/L-band frequencies to offer 100-500 meter penetration and 3-10 meter resolution and is currently operational. Argentina’s SAOCOM system uses L-band, providing 10-20 meter penetration and 10-30 meter resolution, and is operational. Japan’s ALOS-2 PALSAR system uses L-band to deliver 5-15 meter penetration and 10-30 meter resolution and is operational. The European Space Agency’s Biomass system aims for 50-100 meter penetration and 50-100 meter resolution using P-band and is planned for launch in 2025. The US-India partnership NISAR is planned for 2024, using L/S-band to offer 10-20 meter penetration and 3-10 meter resolution. As can be seen, China’s system demonstrates a clear superiority over all existing and planned competitors in terms of both penetration depth and resolution. In particular, the P-band and L-band combination largely eliminates the traditional trade-off between depth and resolution.
Scientific and Civil Application Areas
Geology and Earthquake Prediction
One of the most important civil applications of the underground imaging satellite is the monitoring of active fault lines. While more than 90% of major earthquakes worldwide occur on known active fault lines, our knowledge of the deep geometry of these faults and the amount of accumulated stress is extremely limited. Current methods rely either on surface observations or on a limited number of deep boreholes and seismic measurement stations.
The Chinese satellite can revolutionize earthquake hazard assessments by mapping the depth, inclination and lateral continuity of fault planes from orbit. In particular, critical regions such as the Longmenshan Fault Line (the source of the 2008 Sichuan earthquake), one of the world’s most active fault systems located on China’s own territory, and the eastern extensions of the North Anatolian Fault Line can be continuously monitored.
The elastic deformation accumulating along fault lines changes the dielectric properties underground. The development of micro-cracks in rocks under stress, changes in water content and mineralogical transformations affect the reflection patterns of radar signals. Monitoring these changes over time may enable the detection of earthquake precursors. The China Earthquake Administration (CEA) aims to integrate data obtained from this satellite with existing seismic networks to develop medium-term prediction models, particularly for earthquakes above magnitude 6.
Geothermal Energy and Natural Resource Exploration
The thermal structure of the earth’s crust is critical in determining geothermal energy potential. Hot rock formations, magma chambers and hydrothermal systems exhibit dielectric properties different from the surrounding rocks. The satellite’s P-band radar can detect these thermal anomalies up to depths of 300-400 meters from the surface.
Similarly, mineral deposits and underground water reservoirs can be discovered more quickly and at lower cost thanks to this technology. While traditional mineral exploration methods require intensive drilling and geophysical surveys, satellite-based underground imaging can reduce exploration costs by up to 60% by pre-identifying potential areas.
It is planned to use this technology for mineral and water resource exploration in countries within the scope of China’s Belt and Road Initiative, particularly in Central Asia and Africa. This constitutes the technological pillar of China’s global resource security strategy.
Urban Planning, Infrastructure Safety and Disaster Management
Modern cities rise upon complex underground infrastructure networks: metro tunnels, sewage systems, drinking water networks, electricity and communication cables, natural gas pipelines. The mapping of this infrastructure is often incomplete or outdated, especially in historic cities or rapidly urbanizing areas.
Satellite-based underground imaging enables the non-invasive detection of this infrastructure. In particular, cavities, weak ground zones and underground water flow paths along tunnel routes can be identified in advance during pre-construction ground surveys for metro construction. In monitoring infrastructure aging, leaks in old water pipes can be detected as they change the dielectric properties of the ground. Regarding sinkhole and subsidence risk, underground cavities in karstic terrains can be identified before collapse occurs.
The underground cavity disaster that occurred in Shanghai in 2021, causing a shopping center to collapse, painfully demonstrated the importance of such technology. The new satellite can play a proactive role in preventing similar disasters.
Archaeology: Discovering History Without Digging the Soil
Archaeology is perhaps the field that will benefit most excitingly from underground imaging technology. Worldwide, especially in Mesopotamia, Egypt, China, India and Central America, thousands of yet undiscovered ancient settlements, temples, tombs and infrastructure remains lie buried beneath the soil.
Traditional archaeological discovery relies either on chance finds or surface surveys. While geophysical methods (magnetometer, ground-penetrating radar) are effective, their application over large areas is impractical in terms of time and cost. The satellite-based system can scan hundreds of square kilometers in a single pass, marking potential archaeological sites.
China’s own territory holds enormous potential in this regard. Buried caravanserais along the Silk Road route, Neolithic settlements in the Yellow River basin, submerged cities in the Yangtze delta and undiscovered tombs from the Qin Dynasty are among the targets of this technology. The National Cultural Heritage Administration (NCHA) plans to integrate data obtained from the satellite into national archaeological inventory studies.
Climate Change and Permafrost Monitoring
The thawing of permafrost (frozen ground) due to global warming is a critical issue for both infrastructure safety and greenhouse gas emissions. Permafrost areas in northeastern China and on the Tibetan Plateau have been rapidly degrading in recent years. The satellite’s radar penetration capability allows monitoring of the active layer thickness of permafrost, the distribution of ice lenses within it and thawing processes over wide areas.
This data can be used to assess the safety of infrastructure built on permafrost, such as the Qinghai-Tibet Railway, and to improve climate models. The Tibetan Plateau Research Institute within the Chinese Academy of Sciences (CAS) plans to calibrate regional climate change models by integrating permafrost data obtained from the satellite with existing field measurements.
Military-Strategic Dimension and Global Balances
Detection of Underground Military Facilities
In military strategy, underground facilities are the primary method used to protect the most critical elements, from nuclear weapons to command centers, from missile launch ramps to ammunition depots. During the Cold War, the US and USSR built massive underground complexes carved into mountains; today, countries such as Iran, North Korea and China have moved a significant portion of their military infrastructure underground.
China’s new satellite offers a game-changing capability in detecting these facilities. P-band radar can detect cavities carved into hard rocks such as granite or limestone thanks to the dielectric contrast with the surrounding rock. This is particularly critical for deep underground bunkers (DUGs), meaning command centers and shelters at depths of 100-500 meters; for buried missile silos, namely ballistic missile launch facilities hidden under concrete and soil; for underground tunnel networks, especially fortifications on the Korean Peninsula, the Taiwan Strait coast and South China Sea islands; and for secret underground production facilities in the context of nuclear, chemical or biological weapons production plants.
Nuclear Deterrence and Strategic Stability
The ability to detect the locations and depths of underground military facilities has a direct impact on nuclear deterrence doctrines. The second-strike capability of nuclear weapons largely depends on protecting the weapons and the chain of command from being destroyed in a first strike. If one side knows the location and vulnerabilities of all the other side’s underground facilities, the possibility of completely destroying the second-strike capability with a first strike theoretically increases.
This situation can negatively affect strategic stability. During the Cold War, stability was based on the inviolability of the parties’ second-strike capabilities. The increased transparency of underground facilities can weaken this perception of inviolability and increase the risk of escalation in times of crisis.
However, there is an important nuance here: China, as the country developing this technology, possesses an asymmetric advantage. Whether its own facilities can be similarly detected by the opposing side depends on when rival states achieve similar technology. This temporary window of asymmetry is considered an important factor in China’s strategic planning.
Integration with the Belt and Road Initiative
China’s military-strategic objectives are intertwined with its economic expansion strategy. The ports, railways and energy transmission lines built under the Belt and Road Initiative are also part of the People’s Liberation Army’s (PLA) logistics network. The underground imaging satellite can be used not only to provide ground surveys prior to the construction of this infrastructure but also to detect foreign military presence at strategic points.
For example, this satellite can monitor whether there are secret underground facilities or tunnels of other states around Gwadar Port (Pakistan), Hambantota (Sri Lanka) or the Chinese military base in Djibouti. This is a factor that increases China’s global situational awareness.
The Taiwan Strait and Regional Military Balances
Taiwan is one of the actors investing most heavily in underground military facilities. On the island’s mountainous east coast, there are massive air bases carved into rock (for example, Jiashan and Chihhang underground air bases), submarine shelters and command centers. China’s new satellite can reveal the exact locations, dimensions and potential vulnerabilities of these facilities.
This is a critical intelligence advantage that increases the PLA’s targeting precision and first-strike effectiveness in a potential conflict scenario. Similarly, verifying whether underground fortifications built on artificial islands in the South China Sea have been detected by the opposing side is also possible with this satellite.
Space Surveillance and Counter-Space Capabilities
Since the satellite itself is a space asset, it must be protected against the opposing side’s anti-satellite (ASAT) capabilities. China has likely taken measures to protect this satellite, such as rapid orbit change maneuver capability, a frequency-hopping radar system against electronic jamming, a redundant satellite constellation architecture (even if one satellite is lost, the others continue the mission), and ground backup and rapid launch capability (quickly placing a replacement into orbit in case of loss).
International Law, Ethics and Regulatory Issues
Underground Surveillance within the Framework of Space Law
Current international space law is primarily based on the 1967 Outer Space Treaty. This treaty envisages the use of space for peaceful purposes but does not explicitly prohibit military satellites and reconnaissance activities. The interpretation of the term “peaceful” has been controversial since the Cold War and is in practice accepted to cover non-aggressive military uses.
In the context of the underground imaging satellite, the following legal questions arise: Within the framework of national sovereignty and underground privacy, a state’s airspace sovereignty is defined, but what about the underground? Since observation from space is not considered a violation of airspace, should underground surveillance be evaluated in the same category? In the context of detecting cross-border underground resources, how should the detection of underground resources within the Exclusive Economic Zone (EEZ) by another state be evaluated under the United Nations Convention on the Law of the Sea (UNCLOS)? Regarding the detection of military facilities and espionage, is the systematic scanning of a state’s underground military facilities by another state lawful in peacetime? There are no clear answers to these questions yet, and the international community will need to develop new norms on this issue.
The Ethical Dimension: The Right of the Invisible
Throughout human history, the underground has been a shelter, a hiding place. Caves were the refuge of early humans; underground cities were the sanctuary of those fleeing persecution; deep bunkers were the last bastion of leaders under nuclear threat. The elimination of this “invisibility” characteristic of the underground by technology brings with it a philosophical and ethical problem: In a world where everything can be seen, will there remain a spatial dimension to privacy and security?
Especially when it comes to archaeological sites, this technology also questions the balance between “discovery” and “respect.” Ancient tombs, sacred sites and the ancestral lands of indigenous peoples may not wish to be discovered. The ability of technology to detect these areas non-invasively is an advantage, but how this information will be used and who will control it is a critical ethical issue.
Arms Race and Technological Proliferation
This technological leap by China will inevitably trigger a response. The US, European Union, Russia and India are expected to accelerate their programs to develop similar or superior capabilities. The “Subterranean Challenge” and “Earth MRI” programs run by the US through DARPA, the ESA’s Biomass mission and Russia’s Kondor-FKA series are the first signals of this race.
The cost of this new arms race is not only economic but also strategic. To the extent that the increased transparency of the underground shakes the fundamental assumptions of nuclear deterrence, states may turn to riskier strategies: greater investment in mobile launch platforms, increasing underwater nuclear capability or accelerating space-based weapon systems.
Regulatory Proposals
The following steps can be proposed for the international community to adapt to this new technology: Regarding the development of underground surveillance norms, rules of conduct concerning the use of underground surveillance technologies should be developed within the UN Committee on the Peaceful Uses of Outer Space (COPUOS). In the context of transparency and confidence-building measures, states should mutually notify the existence and capabilities of such satellites and conclude bilateral agreements limiting the targeting of military facilities. Within the framework of scientific cooperation, the sharing of data obtained from this technology in civilian fields such as geology, archaeology and disaster management should be encouraged. According to the ethical framework, the consent of the relevant country and local communities should be sought in the detection of archaeological and cultural sites; the commercialization and exploitation of data should be prevented.
Future Perspective and Conclusion
China’s new-generation underground imaging satellite represents a breaking point in the way we perceive the Earth. This technology, capable of penetrating beyond the surface into the earth’s crust, has the potential to revolutionize numerous fields, from scientific discovery to military intelligence, from urban planning to archaeology.
However, this potential also brings with it serious responsibilities and risks. The risk of military espionage and strategic instability, gaps in international law and ethical dilemmas stand before us as the consequences of the uncontrolled proliferation of the technology.
In the short term (1-3 years), the intelligence advantage China will gain from this satellite will affect military balances, especially in the Indo-Pacific region. In the medium term (3-7 years), as other major powers develop similar systems, underground transparency will become a global phenomenon and nuclear strategies will be reshaped. In the long term (7-15 years), this technology may become a standard tool in civil applications such as earthquake prediction, resource exploration and climate change monitoring, and may profoundly transform humanity’s relationship with its planet.
Ultimately, China’s technological achievement is as much a product of human curiosity and the desire for exploration as it is a manifestation of great power competition. This dual nature is the fundamental dynamic that will determine how the technology is used and what it brings to humanity. What is promising is that the same satellite can both save thousands of lives by predicting an earthquake in advance and enrich our common human heritage by discovering a buried ancient city. Technology itself is neutral; whether we use it for the benefit or harm of humanity will be our common choice.
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Sefa Yürükel
Danish ethnographer and social anthropologist (MA)
Aarhus University, 1997
Independent Researcher
Fields of Research: International Politics, Public International Law, Geopolitics, Sociology, Psychology, Cultural Studies, Systems and Structures.
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