Towards High-Resolution Mercury Global Topography from MESSENGER Orbital Stereo Imaging - A Prototype Model for the H6 Quadrangle "Kuiper"

TL;DR

This paper presents a high-resolution digital terrain model of Mercury's H6 quadrangle derived from MESSENGER stereo images, demonstrating improved accuracy and potential for geophysical applications.

Contribution

It introduces a novel photogrammetric workflow combining multi-image matching and block adjustment to produce a detailed Mercury topography model from orbital stereo images.

Findings

DEM has 30 m vertical accuracy

DEM shows excellent agreement with MLA data

Provides a reference for laser altimeter data validation

Abstract

We selected approximately 10,500 Narrow Angle Camera (NAC) and Wide-Angle Camera (WAC) stereo images obtained by the MESSENGER spacecraft during its orbital mission with average resolutions of 150 m/pixel to compute a Digital Terrain Model (DTM) for the so-called H6 quadrangle (Kuiper), extending between 22.5{\deg}S to 22.5{\deg}N and 288.0{\deg}E to 360.0{\deg}E. Among the images, we identified about 21,100 stereo image combinations with each combination consisting of at least 3 images. We applied sparse multi-image matching to derive approximately 250,000 tie-points representing 50,000 ground points. We used the tie-points to carry out a photogrammetric block adjustment, which improves the image pointing and the accuracy of (3D) ground points from about 850 m to approximately 55 m. Subsequently, we applied high density (pixel-by-pixel) multi-image matching to derive about 45 billion tie-points. Benefitting from improved image pointing data, we compute about 6.3 billion surface points. By interpolation, we generated a DEM with a lateral spacing of 221.7 m/pixel (192 pixels per degree) and a vertical accuracy of about 30 m. The comparison of the DEM with the Mercury Laser Altimeter (MLA) tracks obtained over 4 years of MESSENGER operation reveals that the DEM is geometrically very rigid. It may be used as a reference to identify MLA outliers (when MLA operating at ranging limit) or to map offsets of laser altimeter tracks, presumably caused by residual spacecraft orbit and attitude errors. After the relevant outlier removal and corrections, MLA profiles show excellent agreement with topographic profiles from H6 with root mean square height difference of only 88 m.