High Resolution Digital Terrain Models of Mercury

Supplementary material of the article:<br> Tenthoff, M.; Wohlfarth, K.; Wöhler, C. High Resolution Digital Terrain Models of Mercury. <em>Remote Sens.</em> <strong>2020</strong>, <em>12</em>, 3989. <br> Abstract:<br> We refined our Shape from Shading (SfS) algorithm, which has previously been used to<br> create digital terrain models (DTMs) of the Lunar and the Martian surface, to generate high-resolution<br> DTMs of Mercury from MESSENGER imagery. To adapt the reconstruction procedure to the specific<br> conditions of Mercury and the available imagery, we introduced two methodic innovations. First, we<br> extended the SfS algorithm to enable the 3D-reconstruction from image mosaics. Because most mosaic<br> tiles were acquired at different times and under various illumination conditions, the brightness of<br> adjacent tiles may vary. Brightness variations that are not fully captured by the reflectance model may<br> yield discontinuities at tile borders. We found that the relaxation of the constraint for a continuous<br> albedo map improves the topographic results of an extensive region removing discontinuities at<br> tile borders. The second innovation enables the generation of accurate DTMs from images with<br> substantial albedo variations, such as hollows. We employed an iterative procedure that initializes the<br> SfS algorithm with the albedo map that was obtained by the previous iteration step. This approach<br> converges and yields a reasonable albedo map and topography. With these approaches, we generated<br> DTMs of several science targets such as the Rachmaninoff basin, Praxiteles crater, fault lines, and<br> several hollows. To evaluate the results, we compared our DTMs with stereo DTMs and laser altimeter<br> data. In contrast to coarse laser altimetry tracks and stereo algorithms, which tend to be affected by<br> interpolation artifacts, SfS can generate DTMs almost at image resolution. The root mean squared<br> errors (RMSE) at our target sites are below the size of the lateral image resolution. For some targets,<br> we could achieve an effective resolution of less than 10 m/pixel, which is the best resolution of<br> Mercury to date. We critically discuss the limitations of the evaluation methodology.<br> <br>