行星际介质在无线电掩星实验中的贡献研究
A study on the contribution of the interplanetary medium in radio occultation experiments
AI总结：
该研究分析5组航天器无线电掩星数据集，量化行星际介质对多普勒噪声的贡献，证明双向相干链路的等离子体灵敏度，为相关研究提供约束。
AI中文摘要：
行星际介质（IPM）中的电子密度不规则性会导致航天器无线电信号的多普勒频率波动，波动幅度取决于载波频率、传播几何和链路配置等因素。然而，目前对不同频率下各类掩星实验中该效应的定量表征仍有限。我们分析了5组互补数据集：月电离层外的月船3号双向S波段观测数据、月船2号在月球掩星期间的双向S波段数据、仅受IPM影响的金星快车无线电科学（VeRa）/拂晓号无线电科学（Akatsuki）的单向S/X波段测量数据，以及拂晓号在太阳掩星期间的单向X波段数据。月船3号和拂晓号的IPM观测通过排除行星大气、月电离层（太阳掩星期间除外）和太阳日冕的贡献，分离出IPM效应；月船3号数据采样了动态演化的地月几何，呈现出微弱的毫赫兹级多普勒波动，月船2号观测则在太阳和地磁平静条件下提供了近月等离子体基准，幅度更高；拂晓号和VeRa的仅IPM测量捕捉了长路径行星际效应，而拂晓号太阳掩星数据则揭示了强日冕信号。功率谱密度分析表明，月球掩星和太阳掩星案例呈现类柯尔莫哥洛夫湍流特征，而仅IPM的光谱显示低幅度波动。这些结果量化了IPM对多普勒噪声的贡献，证明了双向相干链路的等离子体灵敏度增强，并为湍流建模、精密航天器跟踪及无线电掩星实验的解释提供了约束。
英文摘要：
Irregularities in electron density within the interplanetary medium (IPM) can cause fluctuations in the Doppler frequency of spacecraft radio signals. The amplitude of these fluctuations depends on factors such as the carrier frequency, propagation geometry, and link configuration. However, quantitative characterization of these effects across different frequencies in various occultation experiments is currently limited. We analyze five complementary datasets: two-way S-band observations from Chandrayaan-3 outside the lunar ionosphere, two-way S-band data from Chandrayaan-2 during lunar occultation, one-way S/X band measurements from the Venus Express Radio Science (VeRa)/Akatsuki Radio Science (Akatsuki) under IPM-only conditions, and one-way X-band Akatsuki data during solar occultation. The Chandrayaan-3 and Akatsuki IPM observations isolate IPM effects by excluding contributions from planetary atmospheres, the lunar ionosphere, and, except during solar occultation, the solar corona. Chandrayaan-3 data sample dynamically evolving Earth-Moon geometries and exhibit weak, mHz-level Doppler fluctuations, while Chandrayaan-2 observations provide near-lunar plasma benchmarks with higher amplitudes, during quiet time solar and geomagnetic conditions. Akatsuki and VeRa's IPM-only measurements capture long-path interplanetary effects, whereas Akatsuki solar occultation data reveal strong coronal signatures. Power spectral density analysis indicates Kolmogorov-like turbulence for lunar occultation and solar occultation cases, while IPM-only spectra show low-amplitude fluctuations. These results quantify the IPM contribution to Doppler noise, demonstrate the enhanced plasma sensitivity of two-way coherent links, and provide constraints relevant to turbulence modelling, precision spacecraft tracking, and the interpretation of radio occultation experiments.
