November 2, 2024

See Mars Like Never Before With Tianwen-1’s High-Resolution Global Map

China’s First Mars Global Color Image Map in Robinson ProjectionChina’s First Mars Global Color Image Map in Robinson Projection
A true color Mars global image map in Robinson projection is created with Tianwen-1 MoRIC image data, the resolution of the original data is ~76 m per pixel, and the horizontal accuracy is 68 m. Credit: ©Science China Press

Researchers leveraging the Tianwen-1 mission’s data have developed a high-resolution global color-image map of Mars, achieving an unprecedented resolution of 76 meters and enhancing the color authenticity of Mars images.

This new map, built using cutting-edge image processing techniques, now serves as a vital geographic reference for Mars exploration and research, potentially revolutionizing our understanding of the Martian surface.

Mars Remote Sensing

Remote-sensing images of Mars contain rich information about its surface morphology, topography, and geological structure. These data are fundamental for scientific research and exploration missions of Mars. Prior to China’s first Mars exploration mission, data from six advanced optical imaging systems of different missions in the Martian orbit have been used to generate Mars global/near-global image datasets with spatial resolutions better than 1 km.

However, in terms of global color images, the best version of Mars Viking Colorized Global Mosaic has a resolution of ~232 m/pixel. There is a lack of global color images of Mars at the hundred-meter scale and higher resolution.

MoRIC and MMS Exploration IllustrationMoRIC and MMS Exploration Illustration
The optical camera (MoRIC) and imaging spectrometer (MMS) onboard the Tianwen-1 orbiter were used to obtain remote-sensing images of the entire Martian surface. MoRIC employs a step-starting frame imaging technique with a color-imaging sensor and obtains Martian surface image data along the flight direction when the orbital arc is below an altitude of 800 km at the periareion. At an orbital altitude of 265 km near the periareion, the imaging swath was 265 km and the resolution was 65 m/pixel. MMS is a linear array push-broom imaging spectrometer that collects spectral images in the visible and near-infrared wavelengths. The imaging swath was 55 km at an orbital altitude of 265 km near the periareion, and the spatial resolution was 265 m/pixel. The MMS obtains spectral data simultaneously while the MoRIC is operating. Credit: ©Science China Press

Advancements With Tianwen-1

New data obtained by Tianwen-1 mission have laid the foundation for the development of a high-resolution global color-image map of Mars with high positioning accuracy. As of July 25, 2022, Tianwen-1 Moderate Resolution Imaging Camera (MoRIC) had completed imaging over 284 orbits during its remote-sensing mission period, acquiring 14,757 images with spatial resolutions between 57 and 197 m.

The collected images achieved global coverage of the Martian surface. At almost the same time, a total of 325 strips of data in the visible and near-infrared bands were obtained by Tianwen-1 Mars Mineralogical Spectrometer, with spatial resolutions varying from 265–800 m.

MoRIC Images Correction ProcessingMoRIC Images Correction Processing
(a) Level 2C data product as the input, (b) image corrected by atmospheric correction, (c) image corrected by photometric correction, and (d) image corrected after color correction. Credit: ©Science China Press

Methodology and Technological Enhancements

With the above-mentioned data, Professor Li Chunlai at National Astronomical Observatory of the Chinese Academy of Sciences, and Professor Zhang Rongqiao at Lunar Exploration and Space Engineering Center, have led the Tianwen-1 science team and collaborators to conduct the research of image data processing and global mapping of Mars. This study used the bundle adjustment technology to optimize the original orbit measurement data by treating Mars as a unified adjustment network, reduce the position deviation between individual MoRIC images to under 1 pixel, and achieving pixel-level “seamless” global image mosaicking.

Brightness and color consistency of the global images were ensured through color correction and global color uniformity. The true colors of the Martian surface were measured using the MMS onboard the Tianwen-1 orbiter, and a true-color reference for the Martian surface was established for true color restoration. Through this study, A global color image dataset and map of Mars (Tianwen-1 Mars Global Color Orthomosaic 76 m v1), with a resolution of 76 m and a horizontal accuracy of 68 m was produced and released.

Impact of the Tianwen-1 Mars Global Color Orthomosaic

The Tianwen-1 Mars Global Color Orthomosaic data products fill the gap in the high-precision positioning of Mars global color-image data products at a scale of tens of meters. It is currently the highest resolution global true-color image map of Mars, and significantly improves the resolution and color authenticity of commonly used global Mars images. This mapping product can serve as a new Mars global base map, providing a higher-quality geographic reference for international peers to conduct Mars image mapping at scales of tens of meters, meters, and submeters, as well as supporting subsequent Mars exploration missions and scientific research.

Reference: “A 76-m per pixel global color image dataset and map of Mars by Tianwen-1” by Jianjun Liu, Xin Ren, Wei Yan, Wangli Chen, Xingguo Zeng, Xiaoxia Zhang, Xu Tan, Xingye Gao, Qiang Fu, Dingxin Liu, Lin Guo, Qing Zhang, Jingjing Zhang, Guobin Yu, Zhiping He, Yan Geng, Rongqiao Zhang and Chunlai Li, 23 April 2024, Science Bulletin.
DOI: 10.1016/j.scib.2024.04.045