E-THEMIS Thermal Anomaly Simulation Observations

This dataset contains 100,000 simulated observations of Europa with the E-THEMIS instrument. Each observation was generated by randomly selecting (1) one of 46 planned Europa flybys by the Europa Clipper from the 17F12_V2 trajectory and (2) the distance of the spacecraft to Europa (±50,000 km from closest approach). We used the KRC thermal model to simulate the Europa surface temperature as a function of latitude, longitude, and local solar time (Sun position). We simulated the appearance of Europa within the E-THEMIS field of view given the Europa radius of 1591 km. We used ray tracing to determine, given the surface temperature model and the relative positions of Europa and the spacecraft, the amount of thermal radiation from Europa that a given pixel would collect. We used Monte Carlo integration over 100 uniformly random sub-pixel locations within each pixel. We injected artificial thermal anomalies into the simulated Europa observations by selecting a random radius between 1 m and 25 km and random temperature between 75 K and 275 K, then modifying the modeled surface temperature. We used an instrument model that converts temperature to digital numbers to generate the final E-THEMIS data product. The ethemis_dn_to_temp.npz file contains the mapping from digital number to temperature in each of the three E-THEMIS bands. Each observation is also a NPY-formatted file containing the following entries: event_time: the simulated time at which the observation was acquired trial: the trial identifier (should match the file name) samples: the number of samples used in the Monte Carlo integration anomaly_radius_m: the (circular) anomaly radius in meters temperature: the temperature of the anomaly band1_dn: the digital number for each pixel in the observation (similar entries exist for the other bands) band1_mask: a mask specifying the fraction of each pixel containing an anomaly (similar entries exist for the other bands) The extracted dataset is roughly 18 Gb in size.本数据集包含100000次木卫二（Europa）搭载E-THEMIS仪器（E-THEMIS）的模拟观测数据。每条观测数据均通过两步随机选取生成：其一，从17F12_V2轨道计划的46次欧罗巴快船（Europa Clipper）飞掠任务中随机选取1次计划飞掠；其二，随机选取航天器距木卫二的距离（取值范围为最接近点±50000千米）。研究团队采用KRC热模型（KRC thermal model），模拟木卫二表面温度随纬度、经度及当地太阳时（太阳位置）的变化规律。基于木卫二半径1591千米的参数，模拟木卫二在E-THEMIS视场内的成像效果。结合表面温度模型与木卫二、航天器的相对位置，采用光线追踪法计算每个像素所接收的木卫二热辐射总量。随后对每个像素内的100个均匀随机亚像素位置开展蒙特卡洛积分运算。通过随机选取1米至25千米范围内的圆形异常半径，以及75开尔文至275开尔文范围内的异常温度，修改建模得到的表面温度，以此向模拟观测数据中注入人工热异常。采用将温度转换为数字量的仪器模型，生成最终的E-THEMIS数据产品。其中"ethemis_dn_to_temp.npz"文件包含三个E-THEMIS波段各自的数字量到温度的映射关系。每条观测数据均为NPY格式文件，包含以下字段："event_time"：模拟观测的采集时刻；"trial"：试验标识符（需与文件名一致）；"samples"：蒙特卡洛积分所用的样本数量；"anomaly_radius_m"：以米为单位的圆形异常半径；"temperature"：异常温度；"band1_dn"：观测中每个像素的数字量（其余波段存在类似字段）；"band1_mask"：标注每个像素包含异常比例的掩膜（其余波段存在类似字段）。该提取后的数据集总大小约为18吉字节（Gb）。