Planetary Mapping with the Wu Bo Team: Chang'e Landing Sites and Tianwen-1 Martian Terrain Modelling

Integrated Information Database of The Hong Kong Polytechnic University (PolyU) · Module 04 Research This dossier focuses on the research thread of high-precision 3D terrain mapping, automatic crater/boulder identification and landing-site safety assessment pursued by the team of Professor Wu Bo in the Department of Land Surveying and Geo-Informatics — a parallel pillar to the "Mars Camera" (Yung Kai-leung's team) and the "sample-packing system". This article covers the remote-sensing mapping research strand. For the Mars camera, see mars-camera-tianwen.md; for the lunar sampling system, see lunar-sampling-system.md; for the RCDSE institutional file, see deep-space-exploration-research-centre.md; for the aerospace overview, see aerospace-and-space.md.

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# 1. Who is Wu Bo? From surveying to planetary mapping

Professor Wu Bo^※ is the Chung Hon-Zen Professor of Space Science at PolyU, and concurrently Associate Head of the Department of Land Surveying and Geo-Informatics and Deputy Director of the Research Centre for Deep Space Explorations (RCDSE). His disciplinary roots lie in photogrammetry and remote sensing, with research interests spanning planetary terrain mapping, planetary science and 3D GIS applications. Wu earned his doctorate in engineering from Wuhan University and completed postdoctoral research at The Ohio State University between 2006 and 2009, where he worked on NASA-funded lunar and Martian exploration projects. He joined PolyU in 2009 and formally made planetary mapping a core research strand.

This background places him in a role distinct from the "precision mechanical engineering" route within PolyU's aerospace research community: the Yung Kai-leung team focuses on instrument development (cameras, sampling systems); the Wu Bo team focuses on remote-sensing data analysis and terrain modelling — in short, "using data to see the terrain clearly and assess whether a safe landing is possible." Together the two constitute the twin engines of PolyU's deep-space exploration effort (the dual-director structure at the institutional level is covered in deep-space-exploration-research-centre.md), and form one of the two main threads of the University's aerospace research layout that has run for over a decade since 2010 (for the full timeline, see aerospace-program-overview.md).

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# 2. What the Wu Bo team does: core technical approaches

# How is high-precision 3D terrain reconstruction achieved?

The team's core technology is planetary 3D mapping through the integration of multi-source remote-sensing data. According to the RCDSE profile of Professor Wu Bo^※, his research directions cover photogrammetry and machine vision, planetary mapping and planetary science, and 3D geographic information systems and their applications. More specifically, the technical methods applied to the lunar and Martian missions include:

• Multi-source data fusion: co-registering orbiter imagery (such as the Chang'e-2 CCD camera and NASA's LRO laser altimeter), descent-camera images and stereo pairs from rover navigation cameras into a unified geographic framework, producing high-precision terrain products;
• Shape from Shading (SFS): recovering 3D features from image brightness and albedo information to enhance terrain resolution in data-sparse regions — in research published in the ISPRS Journal of Photogrammetry and Remote Sensing^※, the Wu Bo team used exactly this class of method on high-resolution Lunar Reconnaissance Orbiter imagery for fine-scale lunar surface reconstruction;
• Machine learning: developing AI algorithms to process satellite imagery for automatic identification and quantitative analysis of geomorphological features such as craters and boulders — according to the PolyU PAIR interview briefing^※, this has "significantly improved research efficiency and reliability."

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

# Why do crater and boulder analyses matter?

Landing safety depends heavily on terrain detail. Crater rims and interior slopes can tip a lander over; scattered boulders can block a rover's path or jam its wheels; ground undulation beyond a threshold directly endangers a soft-landing attempt. A core contribution of the Wu Bo team is precisely the development of algorithms that can quantify these features quickly, at scale and automatically, feeding the results into the mission team's landing-zone decisions.

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# 3. The Chang'e-3 and Chang'e-4 lunar missions: from Sinus Iridum to the far side of the Moon

# Chang'e-3: multi-source data integration sets a precedent

The team's first planetary-mapping engagement in practice came with Chang'e-3 (which landed on the lunar nearside in the Mare Imbrium region in 2013). According to the ISPRS conference paper^※ and related studies, the team integrated Chang'e-2 CCD imagery (at 7 m and 1.5 m resolution), descent-camera images and stereo pairs from the rover's navigation cameras into a unified geodetic framework, generating high-precision terrain products with a maximum resolution of 0.05 m. For every stopping point of the Yutu rover, they routinely produced local digital elevation models (DEMs) at 0.02 m resolution, directly supporting ground-based tele-operation decisions. This was the first case in which PolyU systematically applied multi-source mapping techniques to support an operational national lunar mission.

# Chang'e-4's Von Kármán crater: 400,000 craters, 20,000 boulders

Chang'e-4 was the first soft landing in human history on the far side of the Moon (landing on 3 January 2019 in the Von Kármán crater in the South Pole–Aitken basin). The Wu Bo team had been commissioned by the China Academy of Space Technology to carry out terrain and geomorphology analysis of candidate landing zones as early as March 2016.

According to a Sina News report^※:

• The team collected lunar remote-sensing data from multiple sources and built high-precision, high-resolution terrain models for two candidate landing zones;
• They analysed the distribution, size and density of more than 400,000 craters and over 20,000 boulders within the candidate zones;
• They identified the largest boulder in the zone at up to 35 metres in diameter;
• They computed ground-slope distributions to locate relatively flat areas suitable for a safe landing;
• The highest-priority landing sub-region recommended by the team was exactly where Chang'e-4 ultimately landed.

After the successful landing, the team further determined the lander's position precisely by integrating orbiter, descent-camera and ground-camera imagery, and developed visual localisation technology for the Yutu-2 rover, sustaining its daily ground operations and path planning. They subsequently carried out centimetric-resolution modelling, measuring more than 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 did the candidate zones shrink from three globally to one?

This is the largest in coverage and longest in duration of the Wu Bo team's landing-site selection projects to date. According to the China News Service interview^※ and the Mirage News report^※, the process unfolded in three phases:

Phase 1 (2016–2020) — global assessment and shortlisting to three zones: In 2016, Wu Bo was invited by the China Academy of Space Technology to lead a global assessment of Martian terrain and geomorphology. Combining multi-dimensional criteria — elevation, slope, boulder abundance, crater density and geological context — the team shortlisted three candidate zones from across the planet:

After comprehensive evaluation, southern Utopia Planitia was identified as the target landing zone — it is the largest known impact basin in the Martian northern hemisphere, with comparatively flat terrain meeting soft-landing safety requirements.

Phase 2 (February–May 2021) — fine modelling from high-resolution images: After Tianwen-1 entered orbit around Mars in February 2021, it began photographing the target landing zone at high resolution. The team started processing images from mid-March, completing 3D modelling analysis in roughly two months. They handled millions of boulders, hundreds of thousands of craters and other terrain features that could affect landing safety, using AI-based automatic identification to reach roughly 85% accuracy in feature extraction. From this, they delineated several feasible landing ellipses for the mission management team to make the final confirmation.

Outcome: Tianwen-1 landed successfully in southern Utopia Planitia on 15 May 2021, deploying the Zhurong rover — achieving China's first soft landing on Mars.

# How did Wu Bo assess the work?

In a later interview with China News Service, Wu Bo remarked: "We have not only witnessed history — we are also part of it; we took part in history." He also noted that it took the United States about 20 years to complete the "orbit, land, rove" three-step Mars exploration strategy, whereas China achieved all three steps in a single Tianwen-1 mission — a "very great achievement." (Source: China News Service^※)

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# 5. National recognition: two RCDSE members receive national awards

According to the PolyU PAIR newsletter, Issue 8^※ (December 2023):

Within the Research Centre for Deep Space Explorations (RCDSE), Professor Wu Bo and Professor Yung Kai-leung (RCDSE Director) both received the Outstanding Award — a personal honour conferred jointly by six ministries and commissions including the Ministry of Industry and Information Technology and the China National Space Administration. Wu's award recognised his terrain-mapping and geomorphology-analysis technology for safely identifying the Tianwen-1 Mars landing zone; Yung's recognised his leadership in developing the surface-sampling and sealing system that supported Chang'e-5's lunar sample collection. In addition, the PolyU team received a team award for the Chang'e-5 mission.

This is formal endorsement by the national space authorities of PolyU's mapping contributions — the two professors respectively representing the two parallel PolyU aerospace research routes of "engineering instrumentation" and "remote-sensing mapping."

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# 6. Chang'e-5 and Chang'e-6: mapping support extended to sample return

The Wu Bo team's involvement in lunar mapping did not stop at Chang'e-4. According to research records retrieved (the PolyU Scholars IRA^※ and related papers), the team extended its terrain-mapping and lander-localisation techniques to the Chang'e-5 (2020) and Chang'e-6 (2024) sample-return missions, providing technical support for landing-zone terrain analysis and precise lander positioning. In this, they collaborated with Yung Kai-leung's sample-packing system (see lunar-sampling-system.md) on two dimensions — "knowing exactly where to land" and "collecting samples at the landing point."

# Chang'e-6: centimetric-grade re-verification of the Apollo basin on the far side

Chang'e-6 was the first sample-return mission in human history from the far side of the Moon, landing on 2 June 2024 on the southern rim of the Apollo basin in the South Pole–Aitken basin — a large impact basin about 492 km in diameter. The Wu Bo team subsequently worked with mainland Chinese research institutions on a finer re-verification survey of the landing zone. According to the paper in Icarus^※ (published in 2026), the team generated terrain models from orbiter imagery and descent-camera data, fixing the Chang'e-6 landing site precisely at 153.9776°W, 41.6251°S, at an elevation of about −5,273 m. The analysis shows that the landing-zone surface is mainly covered by mare material ejected from a nearby unnamed crater about 51 m in diameter, accounting for roughly 30%–35% of the volume. This finding provides independent terrain-level corroboration for interpreting the provenance of the returned lunar soil samples.

An official newsletter from PolyU's Department of Land Surveying and Geo-Informatics likewise notes that the team's contributions across the Chang'e-5 and Chang'e-6 missions spanned lunar geological study, landing-zone terrain and geomorphology analysis, scientific payload development and depth analysis of lunar soil — an interdisciplinary team rather than a single mapping group underpinning mission operations.

# Summary of Chang'e-5/6 positioning methods

(Data source: Icarus, 2026)^※

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# 7. Present and future: Chang'e-7 and Tianwen-2

Wu Bo's planetary mapping work did not end with Tianwen-1's success. According to the PolyU PAIR news item (May 2024)^※, his team is currently conducting preparatory research for Chang'e-7 and Tianwen-2:

• Chang'e-7: a resource-survey mission to the lunar south polar region, requiring fine mapping and assessment of the lunar south pole's terrain;
• Tianwen-2: a asteroid sample-return mission targeting small bodies that are irregular in shape and extremely limited in surface-terrain information. Wu Bo's team notes that "no ready-made information or data" is the core challenge of this mission; the team has built a test environment in the laboratory that simulates actual planetary conditions, developing mapping methods and landing-site assessment frameworks suited to irregular small bodies, and further integrating AI to improve the efficiency and reliability of satellite-image processing.

These two missions respectively represent the extension of lunar mapping into the deep polar regions, and the expansion of deep-space mapping toward more complex classes of celestial body.

# Tianwen-2 has already borne out the "no prior data" challenge

The challenge Wu Bo's team described has been confirmed in the mission's actual progress. According to the Chinese Academy of Sciences^※, Tianwen-2 was launched on 29 May 2025 from the Xichang Satellite Launch Centre aboard a Long March 3B rocket — China's first probe dedicated to asteroid exploration and sample return. Its target is the near-Earth quasi-satellite asteroid 2016 HO3 (Kamoʻoalewa), after which it plans a flyby of the main-belt comet 311P. The overall mission period is about ten years.

According to the China National Space Administration^※, the probe first captured images of its target asteroid on 6 June 2026, achieved co-planar flight with it on 7 June, and arrived at roughly 2,000 km from the asteroid on 19 June. Using optical navigation data, the mission team continuously refined the asteroid's ephemeris, reducing the position error from an initial order of several hundred kilometres down to the kilometre level — precisely what Wu Bo's team meant by "no ready-made information or data" translated into engineering practice: target asteroid 2016 HO3 is only about 30–100 m in diameter with an extremely weak gravitational field, so any mapping and landing (or attachment) plan must be reconstructed on the spot upon arrival, rather than applying mature models from existing lunar or Martian missions.

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# 8. Position in PolyU's aerospace research landscape

PolyU's role in national deep-space exploration can be understood along two axes: "mapping" and "engineering instrumentation."

The intersection of the two lines: Wu Bo's terrain products give Yung's instruments the "where to land" basis; the in-situ images collected by Yung's instruments, in turn, become one of the raw data sources for Wu's modelling. This internal collaboration is the foundation of PolyU's "combined punch" effect in national-level space engineering (for integration at the level of PolyU's interdisciplinary research platforms, see pair-interdisciplinary-research.md).

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# 9. Witnessing Hong Kong's first spaceflight: Shenzhou-23 launch and Wu Bo's presence

Wu Bo's connection to China's crewed space programme extends beyond the behind-the-scenes work of remote-sensing mapping. On 24 May 2026, the Shenzhou-23 crewed spacecraft lifted off from the Jiuquan Satellite Launch Centre. Its crew included Dr. Li Ka-ying — Hong Kong's first astronaut to enter the Chinese space station Tiangong as a payload specialist, on a roughly six-month mission. According to the PolyU press release^※, PolyU President Professor Teng Jinguang said: "Dr. Li Ka-ying's successful launch is uplifting news for the whole of Hong Kong, marking a new phase in Hong Kong's participation in the nation's space endeavour."

According to the on-site report published on PolyU's official Zhihu account^※, Wu Bo travelled to Jiuquan in person in his capacity as Deputy Director of the RCDSE to witness this historic moment for Hong Kong's space history. He said the experience inspired him to work even harder in future aerospace research and development, so that Hong Kong can participate more deeply in the nation's drive to become a space power and contribute to Hong Kong's innovation and technology development.

Li Ka-ying's selection background also resonates with the talent-cultivation system of PolyU to which Wu Bo's team belongs. She holds a PhD in computer science from the University of Hong Kong, was previously an information-technology and computer-security specialist with the Hong Kong Police Force, and was selected in 2024 by the China Manned Space Agency from roughly 120 Hong Kong candidates, becoming the first Hong Kong payload specialist among the fourth batch of reserve astronauts. Together with the lunar/Martian landing-zone mapping work that Wu Bo's team has long undertaken, this event forms the twin narratives of Hong Kong's participation in national space engineering: "behind-the-scenes remote-sensing support" and "personally experiencing space." For another independent PolyU contribution at the level of communication-navigation satellite payloads, see leo-comm-nav-satellite-payload-2026.md.

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# 10. Sources

• China News Service: Helping Tianwen-1 "witness and take part in history" — a visit with PolyU Professor Wu Bo^※ — Tianwen-1 process, direct quotes from Wu Bo. (June 2021)
• Mirage News: PolyU contributes to Nation's first Mars mission with multidisciplinary research^※ — three-zone shortlisting, candidate-zone assessment criteria, 85% accuracy, quotes from Wu Bo's team. (May 2021)
• PolyU PAIR newsletter Issue 8: National awards recognise RCDSE's contributions to space missions^※ — national awards, background on Wu Bo and Yung Kai-leung's honours. (December 2023)
• PolyU PAIR news: Prof. WU Bo shares on deep space explorations research^※ — Chang'e-7/Tianwen-2 preparatory research, AI applications, team quotes. (May 2024)
• RCDSE profile: Prof. WU, Bo^※ — title, department, research directions. (Official page)
• Sina News: PolyU develops advanced instruments and cutting-edge technology to support the Chang'e-4 lunar mission^※ — Chang'e-4 candidate-zone data: 400,000 craters/20,000 boulders/35 m boulder. (January 2019)
• PolyU Scholars Hub: Effects of illumination differences on photometric stereo shape-and-albedo-from-shading for precision lunar surface reconstruction^※ — SFS/SAfS shape-from-shading technical approach. (ISPRS J., 2018)
• AGU Earth and Space Science: Characterization of the Candidate Landing Region for Tianwen-1^※ — academic source for quantitative characterisation of the Tianwen-1 candidate region. (2021, DOI: 10.1029/2021EA001670)
• Icarus: Detailed topographic and geomorphological analyses of Chang'e-6 landing area^※ — precise coordinates of the Chang'e-6 landing site, mare-material proportion and other academic data. (2026)
• PolyU press release: PolyU congratulates Dr. Li Ka-ying, Hong Kong's first payload specialist, on joining the Shenzhou-23 crewed mission^※ — Li Ka-ying's identity, launch date, President's remarks. (23 May 2026)
• Zhihu · PolyU official account: Hong Kong's first astronaut flies into space for the first time! PolyU Professor Wu Bo witnesses the historic moment at Jiuquan^※ — Wu Bo's on-site witness at Jiuquan, quotes. (May 2026)
• Chinese Academy of Sciences: Tianwen-2 probe successfully launched^※ — Tianwen-2 launch date, target bodies, mission period. (29 May 2025)
• China National Space Administration: Tianwen-2 probe reaches target asteroid for scientific exploration^※ — approach timeline and positioning-accuracy improvement figures. (June 2026)
• For comparison: 04 Research · Research Centre for Deep Space Explorations, 04 Research · Mars Camera, 04 Research · Lunar Sampling System, 04 Research · Aerospace and Space.

This dossier is based on PolyU official press releases, PAIR/RCDSE official web pages, authoritative media interviews and peer-reviewed journals. All planetary-mapping figures (crater counts/boulder counts/accuracy) are drawn from the above sources; for specific numbers, please refer back to the original reports or papers.