Sub-metre Lunar DEM Generation and Validation from Chandrayaan-2 OHRC Multi-View Imagery Using Open-Source Photogrammetry

Abstract

High-resolution digital elevation models (DEMs) of the lunar surface are essential for surface mobility planning, landing site characterization, and planetary science. The Orbiter High Resolution Camera (OHRC) on board Chandrayaan-2 has the best ground sampling capabilities of any lunar orbital imaging currently in use by acquiring panchromatic imagery at a resolution of roughly 20-30 cm per pixel. This work presents, for the first time, the generation of sub-metre DEMs from OHRC multi-view imagery using an exclusively open-source pipeline. Candidate stereo pairs are identified from non-paired OHRC archives through geometric analysis of image metadata, employing baseline-to-height (B/H) ratio computation and convergence angle estimation. Dense stereo correspondence and ray triangulation are then applied to generate point clouds, which are gridded into DEMs at effective spatial resolutions between approximately 24 and 54 cm across five geographically distributed lunar sites. Absolute elevation consistency is established through Iterative Closest Point (ICP) alignment against Lunar Reconnaissance Orbiter Narrow Angle Camera (NAC) Digital Terrain Models, followed by constant-bias offset correction. Validation against NAC reference terrain yields a vertical RMSE of 5.85 m (at native OHRC resolution), and a horizontal accuracy of less than 30 cm assessed by planimetric feature matching.

Figures (8)

• Figure 1: Overview of the OHRC DEM generation pipeline. Stages proceed from multi-view OHRC imagery and stereo pair selection through camera geometry initialisation, sensor model generation (CSM), bundle adjustment (camera parameter refinement), dense stereo correspondence and feature matching, triangulated 3D point cloud reconstruction, DEM interpolation and surface reconstruction, and finally DEM co-registration and void filling to yield the final terrain product.
• Figure 2: DEMs for all five reconstructed regions. Region 5 is included for completeness; its high void fraction reflects the limiting effect of an extreme convergence angle ($\theta \approx 61^{\circ}$) on semi-global matching performance, as discussed in Section \ref{['sec:discussion']}. Regions 2 and 4 have well-filled DEMs with minimal voids. Region 1 was not fully filled using NAC due to the presence of holes in the corresponding NAC DTM. Region 3 has no corresponding NAC reference available.
• Figure 3: Visual feature comparison of OHRC generated DEM vs NAC DTM (both hillshaded) for Sites 1 and 2, randomly selected from Region 4.
• Figure 4: Visual feature comparison of OHRC generated DEM vs NAC DTM (both hillshaded) for Sites 3 and 4, randomly selected from Region 2.
• Figure 5: Terrain profile comparison across Region 4. Horizontal axis: distance along profile transect (m). Vertical axis: elevation (m). Red curve: OHRC DEM. Green curve: NAC DTM reference.