Mars' surface morphology, topography, and geological structure have long been studied through remote-sensing images, which are crucial for scientific research and exploration missions. Before Tianwen-1, global and near-global image datasets were generated from various missions with spatial resolutions exceeding 1 km. However, global color images at resolutions finer than 232 meters per pixel, such as those in the Viking Colorized Global Mosaic, were unavailable, leaving a gap in high-resolution, color-accurate imaging.

The Tianwen-1 mission, which began capturing data on July 25, 2022, has dramatically improved the situation. The mission's Moderate Resolution Imaging Camera (MoRIC) completed 284 orbits during its remote-sensing phase, capturing 14,757 images with resolutions between 57 and 197 meters. These images achieved comprehensive coverage of Mars. Additionally, the Mars Mineralogical Spectrometer (MMS) aboard Tianwen-1 collected 325 strips of data in the visible and near-infrared bands, with resolutions ranging from 265 to 800 meters.

Under the leadership of Professor Li Chunlai from the National Astronomical Observatory of the Chinese Academy of Sciences and Professor Zhang Rongqiao from the Lunar Exploration and Space Engineering Center, the Tianwen-1 science team, along with collaborators, processed the image data to produce a global map of Mars. This involved using bundle adjustment technology to optimize the original orbit measurement data by treating Mars as a unified adjustment network. The position deviation between individual MoRIC images was reduced to less than 1 pixel, resulting in a pixel-level "seamless" global image mosaic. The team ensured brightness and color consistency through color correction, creating a true-color reference for the Martian surface.

The result of this extensive effort is the Tianwen-1 Mars Global Color Orthomosaic 76 m v1, a global color image dataset with a resolution of 76 meters and a horizontal accuracy of 68 meters. This dataset represents the highest resolution true-color image map of Mars available to date, filling the gap in high-precision global color-image data at this scale. The new mapping product is expected to serve as a superior geographic reference for future Mars exploration missions and scientific studies, providing an essential tool for global mapping at scales of tens of meters, meters, and submeters.

Research Report:A 76-m per pixel global color image dataset and map of Mars by Tianwen-1

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