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

摘要

We selected approximately 10,500 Narrow Angle Camera (NAC) and Wide-AngleCamera (WAC) stereo images obtained by the MESSENGER spacecraft during itsorbital mission with average resolutions of 150 m/pixel to compute a DigitalTerrain Model (DTM) for the so-called H6 quadrangle (Kuiper), extending between22.5{\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 combinationconsisting of at least 3 images. We applied sparse multi-image matching toderive approximately 250,000 tie-points representing 50,000 ground points. Weused the tie-points to carry out a photogrammetric block adjustment, whichimproves the image pointing and the accuracy of (3D) ground points from about850 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 billionsurface points. By interpolation, we generated a DEM with a lateral spacing of221.7 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) tracksobtained over 4 years of MESSENGER operation reveals that the DEM isgeometrically very rigid. It may be used as a reference to identify MLAoutliers (when MLA operating at ranging limit) or to map offsets of laseraltimeter tracks, presumably caused by residual spacecraft orbit and attitudeerrors. After the relevant outlier removal and corrections, MLA profiles showexcellent agreement with topographic profiles from H6 with root mean squareheight difference of only 88 m.