Geometric properties of water-ice clouds as observed from Jezero Crater in the first 600 sols with the NavCam Instrument onboard Mars2020 Rover, Perseverance

In the first 600 sols of the Mars2020 mission, LS 5.6o to 316.8o, 46 cloud movies and 145 cloud surveys were collected to observe clouds at Jezero Crater, the landing site of Perseverance Rover. Cloud movies were processed using the Mean Frame Subtraction (MFS) method revealing cloud structures, which were subsequently analysed using digital image processing. Two-dimensional Fast Fourier Transforms (FFT) were used to compute cloud structure sizes ranging from 2.90 km to 15.25 km for clouds between 30 km to 50 km altitude, based on coincident Mars Climate Sounder (MCS) vertical profiles of atmospheric water-ice. Same-value thresholding was utilized to detect the cloud structures in MFS-processed and projected cloud movies. The resolution dependence needed to resolve these structures over various thresholds was examined to find multifractal scaling of Mars clouds for resolutions between 0.1 km and 1.6 km. We characterize the multi-scaling observed in the images and its implications for the design of cloud-tracking cameras from the surface as well as cloud-resolving models.在火星2020任务的前600个火星日（sol）期间，针对LS 5.6°至316.8°的观测区域，科研团队共收集了46份云影像序列与145次云系观测数据，用于在毅力号火星车（Perseverance Rover）的着陆点——杰泽罗撞击坑（Jezero Crater）开展云系观测。云影像序列采用平均帧相减（Mean Frame Subtraction, MFS）方法进行预处理以凸显云系结构，随后通过数字图像处理技术开展分析。结合同期火星气候探测器（Mars Climate Sounder, MCS）获取的大气水冰垂直廓线数据，研究人员借助二维快速傅里叶变换（Fast Fourier Transform, FFT）计算得出：在30 km至50 km的高度区间内，云系的结构尺度介于2.90 km至15.25 km之间。研究采用等值阈值法对经MFS预处理并投影后的云影像序列中的云系结构进行识别。团队还针对不同阈值下分辨云系结构所需的分辨率依赖性展开了系统研究，最终在0.1 km至1.6 km的分辨率区间内，发现了火星云系的多重分形标度特征。本研究对影像中观测到的多标度特性进行了表征，并探讨了其对地表云追踪相机设计以及云分辨模式构建的启示意义。