DEM Refinement and Validation on the Lunar Surface Using Shape-from-Shading with Chandrayaan-2 OHRC Imagery

TL;DR

This paper introduces a Shape from Shading framework to improve lunar digital elevation models using Chandrayaan-2 imagery, enabling high-resolution topographic data extraction beyond stereo limitations.

Contribution

The study develops a novel SfS-based method for lunar DEM refinement and validation, expanding topographic data sources from stereo to shading images.

Findings

Measurable surface slope improvements achieved in lunar DEMs.

Fine-scale crater morphology revealed with enhanced topography.

Sensitivity to large pitch angle separation and footprint coverage identified.

Abstract

This study presents a Shape from Shading (SfS) framework to enhance sub-metre resolution lunar digital elevation models (DEMs) using imagery from the Orbiter High Resolution Camera (OHRC) aboard Chandrayaan-2. The framework applies SfS to an independent OHRC image of the same region, enabling SfS not just as a refinement tool, but as a source of new topographic data, unconstrained by stereo baseline limitations. The method is applied across three lunar sites, including the Cyrillus crater, the Vikram landing region, and the lunar south pole (Mons Mouton), with a systematic three-stage parameter sweep on the SfS smoothness weight. Results show measurable topographic enhancement, particularly in surface slope statistics, revealing fine-scale crater morphology previously unresolved. A limiting case is also characterized, where large pitch angle separation between the shading image and stereo pair reduces SfS sensitivity, and partial footprint coverage of the shading image is identified as a factor influencing spatially variable enhancement quality.