AN INVESTIGATION OF 3D MAAR MORPHOMETRY TO UNDERSTAND THE INFLUENCE OF UNDERLYING TOPOGRAPHY ON CRATER SHAPE

2019 ◽  
Author(s):  
Alex Bearden ◽  
◽  
Alison Graettinger ◽  
Joseph Nolan
Keyword(s):  
Author(s):  
Tomomi Omura ◽  
Shinta Takizawa ◽  
Hiroaki Katsuragi

Abstract For a fundamental understanding of terrain relaxation occurring on sloped surfaces of terrestrial bodies, we analyze the crater shape produced by an impact on an inclined granular (dry-sand) layer. Owing to asymmetric ejecta deposition followed by landsliding, the slope of the impacted inclined surface can be relaxed. Using the experimental results of a solid projectile impact on an inclined dry-sand layer, we measure the distance of centroid migration induced by asymmetric cratering. We find that the centroid migration distance xmig normalized to the crater minor-axis diameter Dcy can be expressed as a function of the initial inclination of the target tan θ, the effective friction coefficient μ, and two parameters K and c that characterize the asymmetric ejecta deposition and oblique impact effect: xmig/Dcy = Ktan θ/(1 − (tan θ/μ)2) + c, where K = 0.6, μ = 0.8, and c = −0.1 to 0.3. This result is consistent with a previous study that considered the effect of asymmetric ejecta deposition. The obtained results provide fundamental information for analyzing the degradation of sloped terrain on planetary surfaces, such as crater-shape degradation due to the accumulation of micro-impacts.


Author(s):  
L. Jiang ◽  
H. L. Tsai

This study develops a quantum mechanical model to investigate energy absorption in ultrafast laser of dielectrics. The model investigates the optical property variations, electron temperature, and density changes at femtosecond scales. The ionizations and electron heating are two major factors considered for pulse absorption occurring within the pulse duration. The flux-doubling model is employed to calculate the free electron generation mainly through impact ionization and photoionization. The quantum mechanical treatments are used to account for the specific heat and the relaxation time for free electrons. The time and space dependent optical properties of the dense plasma generated by the ultrafast laser pulse are calculated. The predictions of ablation threshold and ablation depth of fused silica and barium aluminum borosilicate (BBS) are in good agreements with published experimental data. The model greatly improves the accuracy in predicting the ablation depth and can predict the crater shape.


2019 ◽  
Vol 11 (21) ◽  
pp. 2594
Author(s):  
Qiangyi Liu ◽  
Weiming Cheng ◽  
Guangjian Yan ◽  
Yunliang Zhao ◽  
Jianzhong Liu

Craters contain important information on geological history and have been widely used for dating absolute age and reconstructing impact history. The impact process results in a lot of ejected fragments and these fragments may form secondary craters. Studies on distinguishing primary craters from secondary craters are helpful in improving the accuracy of crater dating. However, previous studies about distinguishing primary craters from secondary craters were either conducted by manual identification or used approaches mainly concerning crater spatial distribution, which are time-consuming or have low accuracy. This paper presents a machine learning approach to distinguish primary craters from secondary craters. First, samples used for training and testing were identified and unified. The whole dataset contained 1032 primary craters and 4041 secondary craters. Then, considering the differences between primary and secondary craters, features mainly related to crater shape, depth, and density were calculated. Finally, a random forest classifier was trained and tested. This approach showed a favorable performance. The accuracy and F1-score for fivefold cross-validation were 0.939 and 0.839, respectively. The proposed machine learning approach enables an automated method of distinguishing primary craters from secondary craters, which results in better performance.


2020 ◽  
Vol 35 (7) ◽  
pp. 1450-1457
Author(s):  
Gagan Paudel ◽  
Sergey Khromov ◽  
Martin Kasik ◽  
Hans Jørgen Roven ◽  
Marisa Di Sabatino

It is likely that observation of roughness at crater bottom upon GDMS sputtering is due to differential sputtering of grains.


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