Planetary Surface Mapping by Prof. Wu Bo’s Team: Chang’e Landing Sites and Tianwen Mars Terrain Modelling

The Hong Kong Polytechnic University (PolyU) Integrated Information Database · 04 Research Module This dossier focuses on the core research thread of Prof. Wu Bo and his team from the Department of Land Surveying and Geo-Informatics — spanning high-precision 3D terrain mapping, automated crater and rock detection, and landing-site safety assessment. These projects form a parallel pillar alongside the ‘Mars Camera’ (Prof. Yung Kai-leung’s team) and the ‘Sample Collection and Packaging System’. This dossier is dedicated solely to the remote-sensing and mapping strand of that research. For the Mars Camera, see mars-camera-tianwen.md; for the lunar sampling system, see lunar-sampling-system.md; for the RCDSE institutional profile, see deep-space-exploration-research-centre.md; for an aerospace overview, see aerospace-and-space.md.

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# 1. Who is Prof. Wu Bo? From Surveying to Planetary Surfaces

Prof. Wu Bo^※ is currently the Chung Wai-ching Professor in Space Science at PolyU, as well as the Associate Head of the Department of Land Surveying and Geo-Informatics and the Associate Director of the Research Centre for Deep Space Explorations (RCDSE). His core expertise lies in photogrammetry and remote sensing, and his research focuses on planetary topographic mapping, planetary science, and 3D GIS applications. Prof. Wu earned his PhD from Wuhan University before completing a postdoctoral fellowship at The Ohio State University in the United States from 2006 to 2009. There, he was exposed to NASA-funded lunar and Martian exploration projects. He formally incorporated planetary mapping into his main research agenda upon joining PolyU in 2009.

This background gives him a distinct role within PolyU’s space research ecosystem, separate from the ‘precision mechanical engineering’ approach: Prof. Yung Kai-leung’s team specialises in instrument development (cameras, sampling systems); Prof. Wu’s team specialises in remote-sensing data analysis and terrain modelling — essentially, ‘using data to read the terrain and assess whether it’s safe to land’. Together, they form the two wheels of a chariot driving PolyU’s deep-space exploration work (for the institutional dual-directorship setup, see deep-space-exploration-research-centre.md).

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# 2. What Prof. Wu’s Team Does: Core Technical Approach

# How is High-Precision 3D Terrain Reconstruction Achieved?

The core technology of Prof. Wu’s team is multi-source remote-sensing data integration for planetary 3D mapping. Based on an exclusive interview with Prof. Wu by The Paper^※, the main technical methods include:

• Multi-Source Data Fusion: Co-registering orbiter imagery (such as Chang’e‑2 CCD images, US Lunar Reconnaissance Orbiter laser altimeter data), descent camera imagery, and rover navigation camera stereo pairs into a unified geographic framework, yielding high-precision terrain products.
• Shape from Shading (SFS): Inverting 3D features based on the brightness information from a single image, enhancing terrain resolution in data-scarce regions.
• Machine Learning: Developing deep-learning algorithms for the automated identification and quantitative analysis of terrain features like craters and rocks, allowing vast numbers of targets to be processed rapidly.

This technical chain spans the full scale from orbital remote sensing to in‑situ rover imagery, providing terrain support both before a mission (landing-site selection) and during it (rover localisation and path planning).

# Why is Crater and Rock Analysis So Critical?

Landing safety depends heavily on fine-grained terrain detail. Crater rims and inner slopes can tip a lander over. Scattered rocks can block a rover’s path or jam its wheels. Any surface undulation exceeding a certain threshold directly jeopardises the success rate of a soft landing. One of Prof. Wu’s team’s core contributions has been developing algorithms that can swiftly, massively, and automatically quantify these geomorphological features, with the analysis results being used to inform the landing-site decisions of mission teams.

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# 3. Chang’e‑3 and ‑4 Lunar Missions: From Mare Imbrium to the Far Side

# Chang’e‑3: Pioneering Multi-Source Data Integration

The team’s first practical experience in planetary mapping came with the Chang’e‑3 mission (landed on Mare Imbrium on the near side of the Moon in 2013). According to an ISPRS conference paper^※ and related research, the team integrated Chang’e‑2 CCD imagery (7 m and 1.5 m resolution), descent camera imagery, and navigation camera stereo pairs into a unified coordinate framework. This produced high-precision terrain products with resolutions down to 0.05 m, and for every stop of the Yutu rover, they routinely generated local terrain Digital Elevation Models (DEMs) at 0.02 m resolution to directly support ground-based teleoperation decisions. This was the first instance of PolyU systematically applying multi-source mapping techniques to support actual mission operations within a national lunar exploration programme.

# Chang’e‑4 and the Von Kármán Crater: 400,000 Craters, 20,000 Rocks

Chang’e‑4 was humanity’s first soft landing on the far side of the Moon (landing on 3 January 2019 in the Von Kármán crater within the South Pole–Aitken Basin). Prof. Wu’s team was invited by the China Academy of Space Technology (CAST) in March 2016 to undertake the terrain and geomorphological analysis of the candidate landing region.

According to a Sina News report^※:

• The team gathered lunar remote-sensing data from multiple sources to build high-precision, high-resolution terrain models for two candidate landing regions.
• Within the candidate regions, they analysed the distribution, size, and density of over 400,000 craters and more than 20,000 rocks.
• They identified the presence of massive boulders up to 35 metres in diameter within the candidate zones.
• They calculated slope distributions to locate relatively flat areas suitable for a safe probe landing.
• The highest-priority landing sub-region recommended by the team was precisely where Chang’e‑4 eventually touched down.

After the successful landing, the team further processed orbiter, descent, and ground camera imagery to precisely determine the lander’s position and developed a visual localisation technique for the Yutu‑2 rover, continuously supporting its daily ground operations and path planning. They subsequently carried out centimetre‑resolution modelling, measuring over 310 small craters larger than 0.1 m in diameter from Yutu‑2’s panoramic camera stereo pairs.

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# 4. The Tianwen‑1 Mars Mission: From Global Assessment to Southern Utopia Planitia

# How Was It Narrowed from Three Global Candidates to One?

This was the most extensive and longest-running landing-site selection project undertaken by Prof. Wu’s team to date. As detailed by a China News Service (CNS) interview^※ and a Mirage News report^※, the process unfolded in three stages:

Stage 1 (2016–2020) — Global Assessment and Three-Zone Screening: Invited by CAST in 2016, Prof. Wu led a team to conduct a global topographic and geomorphological assessment of Mars. They analysed multi-dimensional indicators including elevation, slope, rock abundance, crater density, and geological context, selecting three candidate zones from across the globe:

After a comprehensive assessment, the southern part of Utopia Planitia was confirmed as the target landing zone — a region forming the planet’s largest known impact basin in the north, with relatively flat terrain meeting the requirements for a safe soft landing.

Stage 2 (Feb–May 2021) — High‑Resolution Image Fine Modelling: After Tianwen‑1 entered Mars orbit in February 2021, it began capturing high‑resolution images of the target landing zone. The team started processing these once images were received in mid‑March and completed the 3D modelling analysis in about two months. This involved processing millions of rocks, hundreds of thousands of craters, and other features potentially affecting landing safety. Their AI‑assisted automatic recognition achieved about 85% feature extraction accuracy, mapping out multiple feasible landing ellipses for the mission management team’s final confirmation.

Result: Tianwen‑1 successfully landed on the southern Utopia Planitia on 15 May 2021, deploying the Zhurong rover — achieving China’s first successful Mars soft landing.

# What Did Prof. Wu Say About This Work?

In a post-landing interview with CNS, Prof. Wu said: 「我們不僅見證了歷史,同時我們也是歷史中的一部分,我們參與了歷史。」 (“We did not merely witness history; we were, at the same time, part of that history — we took part in it.”) He also noted that while the US took roughly 20 years to complete its three‑step ‘orbit, land, and rove’ Mars exploration strategy, China’s Tianwen‑1 achieved all three in a single mission, calling it 「非常偉大的成就」 (“an immense accomplishment”). (source: CNS^※)

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# 5. National Recognition: RCDSE Members Receive National Awards

As reported in PolyU PAIR Newsletter Issue 8^※ (December 2023):

Within PolyU’s Research Centre for Deep Space Explorations (RCDSE), both Prof. Wu Bo and Prof. Yung Kai-leung (Director of RCDSE) received a joint Outstanding Award from six national ministries and commissions, including the Ministry of Industry and Information Technology and the China National Space Administration. Prof. Wu was recognised for the contribution of his terrain mapping and geomorphological analysis technologies to the landing-site safety identification for the Tianwen‑1 Mars mission; Prof. Yung was recognised for leading the development of the regolith sampling and packaging system for the Chang’e‑5 lunar mission. The PolyU team additionally received a Team Award for the Chang’e‑5 mission.

This represents a formal endorsement by the national space authorities of PolyU’s mapping research contributions — with the two professors respectively representing the ‘engineering instruments’ and ‘remote‑sensing mapping’ strands of PolyU’s parallel space research trajectories.

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# 6. Chang’e‑5 and ‑6: Extending Mapping Support to Sample‑Return Missions

Prof. Wu’s team’s involvement in lunar mapping did not end with Chang’e‑4. According to retrieved research records (PolyU Scholars IRA^※ and related papers), they extended their terrain mapping and lander localisation techniques to the Chang’e‑5 (2020) and Chang’e‑6 (2024) sample‑return missions. This provided technical support for landing‑area terrain analysis and precise lander positioning, complementing Prof. Yung Kai-leung’s team’s sampling and packaging system (see lunar-sampling-system.md). The two teams’ work thus dovetails on the dimensions of ‘knowing where you’ve landed’ and ‘being able to retrieve a sample from that spot’.

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# 7. Present and Future: Chang’e‑7 and Tianwen‑2

Prof. Wu’s planetary surface mapping work did not conclude with the success of Tianwen‑1. According to PolyU PAIR News (May 2024)^※, his team is currently conducting preliminary research for Chang’e‑7 and Tianwen‑2:

• Chang’e‑7: A resource survey mission to the Moon’s south polar region, requiring detailed mapping and assessment of the challenging south polar terrain.
• Tianwen‑2: A sample‑return mission targeting a near‑Earth asteroid — a small celestial body with an irregular shape and very limited existing surface terrain data. Prof. Wu’s team has noted that the ‘absence of ready‑made information and data’ is the core challenge for this mission. The team has built a simulated test field replicating the physical planetary environment within the laboratory, developing mapping methods and landing‑area assessment frameworks suited to irregular small bodies. They are further integrating AI techniques to enhance the efficiency and reliability of satellite image processing.

These two tasks respectively represent an extension of lunar mapping into the more specialised zone of the polar regions and an expansion of deep‑space mapping to encompass more complex celestial body types.

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# 8. Relationship to PolyU’s Broader Space Research Landscape

PolyU’s role in the nation’s deep‑space exploration can be understood along two axes: ‘Mapping’ and ‘Engineering Instruments’:

The intersection of these two lines lies in the fact that Prof. Wu’s team’s terrain products provide the basis for ‘where to land’, informing the instruments built by Prof. Yung’s team. In turn, the in‑situ images captured by Yung’s instruments become one of the raw data sources for Wu’s team’s modelling. This internal collaboration forms the basis of PolyU’s ability to deliver a combined punch in national‑level space engineering.

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