The ChemCam instrument on the Curiosity rover provides chemical compositions of Martian rocks and soils using remote laser-induced breakdown spectroscopy (LIBS). The elemental calibration is stable as a function of distance for Ti, Fe, Mg, and Ca. The calibration shows small, systematically increasing abundance trends as a function of distance for Al, Na, K, and to some extent, Si. The distance effect is known to be due to a dependence with distance on the relative strengths of atomic transition lines. Emission lines representing transitions from relatively low energy levels remain intense at longer distances while emission lines representing transitions from higher energy levels decrease in intensity more rapidly as a function of distance. The multivariate algorithms used to determine elemental compositions rely on a large number of emission lines in many cases, so rather than trying to correct all emission lines, a study was made of the predicted compositions as a function of distance, in order to determine an empirical correction. Abundance trends can be well approximated by a linear trend with distance within the ranges of abundances and distances observed up to ~6 m. Data from 11 distinct geological members and data groups of the Murray formation in Gale crater, Mars, were used to form the model, selecting the members and data groups yielding the best statistics. The model was tested using data from several targets observed from two different distances, and using data from the Kimberley formation, the composition of which is significantly different from the Murray formation, showing that the model works on other compositions beyond those used to build the model. For long-distance observations up to ~6 m, corrections can be made back to an equivalent composition at the median distance of ChemCam observations (2.6 m). The model has been validated up to 6.2 m, although ChemCam is able to observe bedrock targets to >7 m, and iron meteorites to distances of >9 m.

好奇号上的 ChemCam 仪器火星车使用远程激光诱导击穿光谱 (LIBS) 提供火星岩石和土壤的化学成分。作为 Ti、Fe、Mg 和 Ca 的距离函数，元素校准是稳定的。校准显示，作为距离函数的 Al、Na、K 和在某种程度上，Si 的丰度小而系统地增加的趋势。已知距离效应是由于距离对原子跃迁线的相对强度的依赖性。代表从相对低能级跃迁的发射线在较长距离处保持强烈，而代表从较高能级跃迁的发射线强度随着距离的变化而下降得更快。在许多情况下，用于确定元素组成的多元算法依赖于大量的发射线，因此，与其试图修正所有的发射线，不如对作为距离函数的预测成分进行研究，以确定经验修正。丰度趋势可以很好地近似为线性趋势，距离在丰度范围内，观察到的距离高达 ~6 m。来自火星盖尔陨石坑 Murray 地层的 11 个不同地质成员和数据组的数据被用来形成模型，选择产生最佳统计数据的成员和数据组。该模型使用从两个不同距离观察到的几个目标的数据进行测试，并使用来自 Kimberley 地层的数据进行测试，该数据的组成与 Murray 地层有显着差异，表明该模型适用于构建模型以外的其他组成. 对于长达约 6 m 的远距离观测，可以在 ChemCam 观测的中值距离 (2.6 m) 处将校正恢复为等效成分。尽管 ChemCam 能够观察到大于 7 m 的基岩目标和大于 9 m 的铁陨石，但该模型已被验证到 6.2 m。