Stereophotoclinometry (SPC) was the prime method of shape modeling for NASA’s OSIRIS-REx mission to asteroid Bennu. Here we describe the extensive testing conducted before launch to certify SPC as NASA Class B flight software, which not only validated SPC for operational use but also quantified the accuracy of this technique. We used a computer-generated digital terrain model (DTM) of a synthetic asteroid as the truth input to render simulated truth images per the planned OSIRIS-REx observing campaign. The truth images were then used as input to SPC to create testing DTMs. Imaging sets, observational parameters, and processing techniques were varied to evaluate their effects on SPC's performance and their relative importance for the quality of the resulting DTMs. We show that the errors in accuracy for SPC models are of the order of the source images’ smallest pixel sizes and that a DTM can be created at any scale, provided there is sufficient imagery at that scale. Uncertainty in the spacecraft’s flight path has minimal impact on the accuracy of SPC models. Subtraction between two DTMs (truth and simulated) is an effective approach for measuring error but has limitations. Comparing the simulated truth images with images rendered from the SPC-derived DTMs provides an excellent metric for DTM quality at smaller scales and can also be applied in flight by using real images of the target. SPC has limitations near steep slopes (e.g., the sides of boulders), leading to height errors of more than 30%. This assessment of the accuracy and sensitivity of SPC provides confidence in this technique and lessons that can be applied to future missions.

中文翻译：

---

OSIRIS-REx 任务立体光倾斜测量的灵敏度测试。一、数字地形建模的准确性和误差

立体光斜测量 (SPC) 是 NASA 前往小行星贝努 (Bennu) 的 OSIRIS-REx 任务中形状建模的主要方法。在这里，我们描述了在发射前进行的广泛测试，以证明 SPC 为 NASA B 级飞行软件，这不仅验证了 SPC 的操作用途，而且还量化了该技术的准确性。我们使用计算机生成的合成小行星数字地形模型 (DTM) 作为真实输入，根据计划的 OSIRIS-REx 观测活动渲染模拟真实图像。然后将真实图像用作 SPC 的输入来创建测试 DTM。成像集、观测参数和处理技术各不相同，以评估它们对 SPC 性能的影响以及它们对生成的 DTM 质量的相对重要性。我们表明，SPC 模型的准确度误差与源图像的最小像素大小相当，并且只要在该比例下有足够的图像，就可以在任何比例下创建 DTM。航天器飞行路径的不确定性对 SPC 模型的准确性影响很小。两个 DTM（真实值和模拟值）之间的减法是测量误差的有效方法，但有其局限性。将模拟真实图像与 SPC 派生的 DTM 渲染的图像进行比较，可以为较小尺度下的 DTM 质量提供出色的度量，并且还可以通过使用目标的真实图像在飞行中应用。SPC 在陡坡（例如巨石侧面）附近存在局限性，导致高度误差超过 30%。对 SPC 准确性和灵敏度的评估为这项技术和可应用于未来任务的经验教训提供了信心。