The Mars 2020 rover, Perseverance, landed in Jezero crater (18.4663°N, 77.4298°E) on February 18, 2021 to collect samples from Mars that could be returned to Earth by a future Mars Sample Return campaign. While providing a rich sampling opportunity, Jezero also contains numerous landing hazards including scarps, canyons, mesas, dune fields, rock fields, and smaller craters. The Mars 2020 onboard inertial navigation system, which is the same as that used by the Mars Science Laboratory (MSL), only provides a very coarse inertially propagated position, which can have error as large as 3.2 km. The Lander Vision System (LVS) was added to Mars 2020 to reduce this position knowledge error to less than 40 m with respect to an on-board reference map of the landing area. LVS uses a reference map on board to compare with the descent images for lander localization during the terminal stage of Entry, Descent and Landing (EDL). Because the reference map is used directly during EDL, it is critical that it have as little spatial and photometric error as possible. Photometrically, it should resemble as much as possible the real descent images to allow reliable terrain matching. Spatially, it should match as faithfully as possible the real, underlying terrain and contribute minimal error to the final localization solution. On February 18, 2021, the LVS reference map passed its ultimate test. The LVS system executed Terrain Relative Navigation (TRN) flawlessly based on the LVS reference map. In addition to its use for TRN, the local hazard map is also registered to the LVS reference map so that the safe target selection (STS) system can select a safe and reachable landing site. The final error between the site targeted by the STS system and the real landing site is estimated at only 5 m. The exceptional performance of LVS indicates that the reference map met mission requirements with comfortable margin. LVS on Mars 2020 represents the first ever use of a reference map during spacecraft EDL. This breakthrough will have profound implications for future lander missions and the scope of scientific inquiry they are able to address. In this paper, we will describe the necessary precursor steps to building the Jezero Crater LVS map, including the methodology to dejitter Context Imager (CTX) images, improve the CTX sensor model, as well as the process used to validate the LVS map accuracy.

中文翻译：

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从 MRO/CTX 图像为 Mars 2020 Lander 视觉系统制作机载参考地图

火星 2020 火星车 Perseverance 于 2021 年 2 月 18 日降落在 Jezero 陨石坑（18.4663°N，77.4298°E），以从火​​星收集样本，这些样本可能会通过未来的火星样本返回活动返回地球。在提供丰富的采样机会的同时，Jezero 还包含许多着陆危险，包括陡坡、峡谷、台地、沙丘场、岩石场和较小的陨石坑。与火星科学实验室（MSL）使用的相同，Mars 2020 车载惯性导航系统仅提供非常粗略的惯性传播位置，其误差可能高达 3.2 公里。着陆器视觉系统 (LVS) 被添加到火星 2020 中，以将这个位置知识误差减少到小于 40 m，相对于着陆区的机载参考图。LVS 在进入、下降和着陆 (EDL) 的终端阶段使用机载参考地图与着陆器定位的下降图像进行比较。由于在 EDL 期间直接使用参考地图，因此它具有尽可能小的空间和光度误差至关重要。在光度学上，它应该尽可能地类似于真实的下降图像，以实现可靠的地形匹配。在空间上，它应该尽可能忠实地匹配真实的底层地形，并对最终的定位解决方案贡献最小的误差。2021年2月18日，LVS参考图通过了最终测试。LVS 系统基于 LVS 参考地图完美地执行了地形相对导航 (TRN)。除了用于 TRN 之外，本地危险地图也注册到 LVS 参考地图，以便安全目标选择 (STS) 系统可以选择安全且可到达的着陆点。STS 系统目标站点与实际着陆站点之间的最终误差估计仅为 5 m。LVS 的卓越性能表明参考地图以舒适的余量满足了任务要求。LVS on Mars 2020 代表了航天器 EDL 期间首次使用参考地图。这一突破将对未来的着陆器任务及其能够解决的科学探究范围产生深远的影响。在本文中，我们将描述构建 Jezero Crater LVS 地图的必要前导步骤，包括去抖动上下文成像器 (CTX) 图像的方法，改进 CTX 传感器模型，