[论文解读] In-flight calibration of RADEM, the JUICE mission radiation monitor
本文介绍了 JUICE 任务中 RADEM 的在飞行校准活动，通过使用 GCRs 和 BON2020 模型推导将探测器计数转换为粒子通量的校准系数，并将质子 SEP 通量重建与 SOHO/ERNE 测量进行对比验证。
The RADiation-hard Electron Monitor (RADEM) aboard the Jupiter Icy Moons Explorer (JUICE), launched on 14 April 2023, measures high-energy protons and electrons during the cruise phase and will continue throughout the nominal mission. Initial in-flight observations could not be explained by pre-flight ground calibration, motivating an in-flight calibration campaign. We calibrated the RADEM sensors using galactic cosmic rays by progressively increasing detector thresholds, thereby modifying their response to high-energy particles. Threshold-dependent in-flight count rates were compared with theoretical expectations derived from the Badhwar-O'Neill 2020 galactic cosmic ray model and corresponding response functions. These results were used to derive new in-flight calibration coefficients and to develop a flux reconstruction algorithm based on the bow-tie method. In several cases, the in-flight calibration slopes differ by up to an order of magnitude from ground calibration values. Proton fluxes from solar energetic particle events reconstructed with this method agree within a factor of two with independent measurements from the Solar and Heliospheric Observatory. These results demonstrate that RADEM provides accurate proton flux measurements in interplanetary space and is well suited for both single-spacecraft analyses and coordinated multi-mission studies of solar energetic particles. While electrons were clearly detected during the JUICE Lunar-Earth gravity assist, reliable reconstruction of their fluxes requires further analysis.
研究动机与目标
- 解释为什么地面校准未能重现 RADEM 的飞行观测，并为在飞行中重新校准提供动机。
- 描述将探测器阈值与能量沉积通过响应函数联系起来的校准工作流。
- 开发一种通量重建方法（蝴蝶结/ Bow-tie 方案）将探测器计数转化为入射粒子通量。
- 估计 RADEM 传感器阈值的在飞行校准系数并将质子通量与外部数据集进行验证。
提出的方法
- 使用 Geant4 对 GCR 组分在简化航天器遮挡模型下计算 RADEM 响应函数。
- 在 1 au 处使用 BON2020 GCR 通量，调制势 phi ~ 1000 MV，以匹配 2024 年 5 月的飞行数据。
- 将 RADEM 探测头的能量阈值下的计数率作为变量进行模拟，与飞行计数进行比较以推导校准系数。
- 应用基于 Bow-tie 的通量重建算法将 RADEM 计数转换为微分通量。
- 通过分析 Run 1 与 Run 2 数据并排除污染区间来处理 SEP 污染。
实验结果
研究问题
- RQ1在不同阈值下，飞行中校准是否能够重现观测到的 RADEM 飞行中的计数率？
- RQ2在使用 GCR 作为标定源时，RADEM 传感器的 DAC 到能量阈值转换应如何？
- RQ3校准系数与地面结果有何差异，对通量重建有何意义？
- RQ4RADEM 推导的质子通量在 SEP 事件与安静期与独立测量（如 SOHO/ERNE）吻合程度如何？
主要发现
| Detector Head | Sensor # | Trigger | Run | m [MeV/DAC] | b [DAC] |
|---|---|---|---|---|---|
| EDH | 1 | HGLT | 2 | 1.72E-03 ± 9.26E-05 | -0.08 ± 0.05 |
| EDH | 2 | HGLT | 2 | 1.74E-03 ± 2.99E-05 | -0.10 ± 0.01 |
| EDH | 3 | HGLT | 2 | 1.72E-03 ± 2.58E-05 | -0.08 ± 0.01 |
| EDH | 4 | HGLT | 1 | 1.70E-03 ± 2.86E-05 | -0.20 ± 0.01 |
| EDH | 5 | HGLT | 1 | 1.62E-03 ± 2.05E-05 | -0.15 ± 0.01 |
| EDH | 6 | HGLT | 1 | 1.64E-03 ± 2.96E-05 | -0.18 ± 0.01 |
| EDH | 7 | HGLT | 2 | 1.72E-03 ± 2.14E-05 | -0.10 ± 0.01 |
| EDH | 8 | HGLT | 2 | 1.88E-03 ± 2.79E-05 | -0.13 ± 0.01 |
| EDH | 1 | HGHT | 2 | 1.92E-02 ± 2.04E-03 | -0.21 ± 0.61 |
| EDH | 2 | HGHT | 2 | 1.60E-02 ± 7.67E-04 | 0.22 ± 0.23 |
| EDH | 3 | HGHT | 2 | 1.80E-02 ± 7.39E-04 | -0.08 ± 0.22 |
| EDH | 4 | HGHT | 2 | 1.64E-02 ± 6.62E-04 | 0.07 ± 0.20 |
| PDH | 1 | HGLT | 2 | 1.52E-03 ± 4.08E-05 | -0.06 ± 0.02 |
| PDH | 2 | HGLT | 2 | 1.83E-03 ± 3.36E-05 | -0.16 ± 0.02 |
| PDH | 3 | HGLT | 2 | 1.83E-03 ± 2.41E-05 | -0.16 ± 0.01 |
| PDH | 4 | HGLT | 1 | 1.80E-03 ± 3.68E-05 | -0.27 ± 0.02 |
| PDH | 5 | HGLT | 1 | 1.77E-03 ± 3.60E-05 | -0.26 ± 0.02 |
| PDH | 6 | HGLT | 1 | 1.78E-03 ± 4.33E-05 | -0.27 ± 0.02 |
| PDH | 7 | HGLT | 1 | 2.01E-03 ± 4.33E-05 | -0.19 ± 0.02 |
| PDH | 8 | HGLT | 1 | 2.52E-03 ± 6.24E-05 | -0.30 ± 0.04 |
| PDH | 1 | HGHT | 2 | 1.66E-02 ± 8.65E-04 | -0.09 ± 0.26 |
| PDH | 2 | HGHT | 2 | 1.78E-02 ± 3.92E-04 | 0.05 ± 0.12 |
| PDH | 3 | HGHT | 1 | 1.82E-02 ± 3.99E-04 | -0.42 ± 0.12 |
| PDH | 4 | HGHT | 2 | 1.80E-02 ± 2.71E-04 | 0.01 ± 0.08 |
| PDH | 5 | HGHT | 2 | 1.74E-02 ± 2.61E-04 | 0.04 ± 0.08 |
| PDH | 6 | HGHT | 2 | 1.75E-02 ± 3.23E-04 | 0.05 ± 0.10 |
| PDH | 7 | HGHT | 2 | 2.37E-02 ± 6.07E-04 | -0.18 ± 0.18 |
| PDH | 8 | HGHT | 2 | 2.97E-02 ± 3.17E-04 | -0.09 ± 0.09 |
| HIDH | 2 | LGT | 1 | 4.57E-01 ± 2.31E-02 | 7.07 ± 0.45 |
| HIDH | 2 | LGT | 2 | 4.93E-01 ± 2.19E-02 | 7.40 ± 0.43 |
- 为所有 RADEM 传感器推导出新的在飞行校准系数。
- 在若干情形下，在飞行中的校准斜率与飞行前地面值相比差异最多达到一个数量级。
- 使用 Bow-tie 方法重建的 SEP 事件中的质子通量与 SOHO/ERNE 测量在两倍以内的一致性。
- RADEM 能在星际空间提供准确的质子通量测量，并支持多任务 SEP 研究。
- 在 JUICE LEGA 测量中可识别电子，但通量重建需要更为细致的分析。
- 校准显示 HGLT/HGHT 的斜率因探测器与阈值而异，这与电子学和遮挡建模的限制有关。
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