PPARCセミナー (2025/12/12)
PPARCセミナー (2025/12/12)
(1)
[Name]
Haruki Okuda
[Title]
Estimation of the 844.6 nm Emission Height Using AIC-S2 Data from LAMP-ROCKET
[Abstract]
The LAMP-ROCKET sounding experiment aims to investigate the relationship between pulsating aurora, energetic precipitating electrons, and relativistic electron microbursts by means of simultaneous particle, field, and optical measurements. Within this project, the multi-spectral auroral camera AIC2 plays a key role in imaging auroral emissions near the magnetic footprint of the rocket. AIC2 consists of two CMOS cameras: AIC-S1 observing 670 nm emissions from the E region and AIC-S2 observing O I 844.6 nm emissions that are expected to originate mainly from the F region and to be produced by electrons in the keV energy range. AIC-S2 is a wide–field-of-view (FOV ≃ 106°) camera designed to cover the region from the magnetic footprint of the rocket to the limb direction in a single image.
In this study, we use AIC-S2 data from LAMP-ROCKET and aim to estimate the height distribution of the 844.6 nm emission. After background and flat-field corrections and conversion from counts to Rayleigh using pre-flight calibration, we compute line-of-sight vectors in the rocket body frame and transform them into the Earth-fixed frame using attitude data. For each line of sight we calculate the tangential height, i.e., the minimum distance between the ray and the Earth’s surface, and we are preparing a mapping procedure that projects each pixel onto geographic coordinates assuming a given emission height.
At the current stage, we have confirmed that clear O I 844.6 nm auroral emission was captured by AIC-S2 during the LAMP-ROCKET flight and have made preliminary estimates of the approximate location and horizontal scale of the emission region using simple mapping. However, for the time interval analyzed so far, AIC-S2 was looking mostly downward at the aurora rather than toward the limb, which makes it difficult to uniquely determine the emission height from the tangential-height information alone. As future work, we plan to examine the plausibility of the estimated heights by comparison with AIC-S1 and ground-based all-sky imagers, and to move toward deriving more reliable height profiles of the 844.6 nm emission. In this seminar, I will report these preliminary results.
(2)
[Name]
Katoh Takeru
[Title]
Estimation of Titan’s Ionospheric Density Structure using Saturnian Radio Occultation: Preliminary Analysis of the T77 Flyby
[Abstract]
土星系最大の衛星タイタンは、太陽系内の衛星で唯一、分厚い大気を有している。その中性大気は主に窒素から成るが、メタンや炭化水素も含む。また、その電離圏は50種以上のイオンが分子やエアロゾルの生成に寄与するなど、太陽系で最も複雑な組成を持つとされる。
本研究では、Yasuda et al. [年号] によって確立された惑星電波掩蔽法を用い、タイタンの電離圏電子密度構造の推定を行う。解析にはCassini探査機のRPWI（電波・プラズマ波動観測器）によって観測された土星電波データを用いる。具体的には、土星電波がタイタンに掩蔽されるイベント前後のデータを解析し、電離圏による屈折の影響を受けた電波から掩蔽の開始・終了時刻を算出する。
さらに、EXPRESコードを用いて土星電波源からの伝搬経路を計算し、ガウス関数型の電離圏モデルを用いたレイトレーシング・シミュレーションを実施する。観測から得られた掩蔽時刻とシミュレーション結果を比較することでモデルの最適化を行い、電離圏構造を決定する。本発表では、全127回のフライバイのうち、T77フライバイ（77回目）に着目した解析結果について報告する。
Titan, Saturn’s largest moon, is the only satellite in the solar system to possess a thick atmosphere. While its neutral atmosphere is primarily composed of nitrogen, it also contains methane and hydrocarbons. Its ionosphere is considered the most chemically complex in the solar system, with over 50 types of ions contributing to the formation of molecules and aerosols.
In this study, we estimate the electron density structure of Titan’s ionosphere using the planetary radio occultation method established by Yasuda et al. We analyzed Saturnian radio wave data obtained by the Radio and Plasma Wave Science (RPWI) instrument onboard the Cassini spacecraft. Specifically, we examined data around occultation events where Saturnian radio waves passed behind Titan, calculating the start and end times of the occultation based on the refraction caused by the ionosphere.
Furthermore, we performed ray-tracing simulations using a Gaussian ionospheric model, with propagation paths from the radio source calculated via the EXPRES code. By comparing the observed occultation times with the simulation results, we optimized the model to determine the ionospheric structure. This presentation provides an interim report focusing on the analysis of the T77 flyby out of the 127 total flybys.
