中村 正人

Our laboratory measurements of bidirectional reflectance by a layer of olivine particles with radii in 45-212 mu m suggest that the intensity of backscattering light from the rough surface is significantly enhanced, compared with that from the smooth surface. Furthermore, it is found that the backscattering light by rough surface decreases more gradually than that expected by smooth surface with incident angle. This result implies that the light detection and ranging instrument (LIDAR) on HAYABUSA (Japanese asteroid sample return mission, MUSES-C) has a potential ability to reveal the existence of a regolith layer on a very small (<600 in) asteroid 25143 Itokawa (1998SF36) due to enhancement of reflected light of LIDAR in the limb region of the target asteroid, compared with that expected for the smooth bulk surface at the same incident angle. The current status of LIDAR before the in situ measurements scheduled in September-November 2005 is briefly summarized. (C) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

惑星大気圏から宇宙空間への原子の散逸量を測定する方法として,中性粒子・イオンの共鳴散乱光を観測して散逸量を求める方法がある.特に,H・He・O などの共鳴散乱光は極端紫外光領域にあり,極端紫外光を観測可能な光学系の開発が重要である.また,大気の空間分布やその時間変動を観測するためには撮像観測も必要である.この方法では従来,バンドパスフィルターと,その波長を強く反射するよう製作された多層膜反射鏡を組み合わせて,観測対象の散逸原子の共鳴散乱光のみを観測可能な光学系を作成し,衛星・ロケットに搭載して観測を行った.しかし,分光観測ではないので,1 つの光学系で観測可能な共鳴散乱光は1 波長に限られる.複数の原子の共鳴散乱光を同時に観測する場合は複数の光学系が必要となる.1 つの光学系で複数の共鳴散乱光を観測するには,通常,光学系に分光器を組み込んで観測を行う.だが,反射鏡と分光器を用いた場合を比較すると,一般的に分光器は光量の損失が多い.今回はヘリウムイオンの共鳴散乱光(30.4 nm)を強く反射するように,最上層にSi :5.0 nm,その下にMo : 4.4 nm とSi : 13.3 nm のペア20 層を回折格子に蒸着し,極端紫外光用のMo/Si 多層膜回折格子を製作し,性能評価を行った.多層膜を蒸着しても回折格子の溝が埋まらないことを原子間力顕微鏡で確認した.また,多層膜回折格子の反射効率は,ブレーズ型が最大2.2 %,ラミナー型が最大2.9 % であった.多層膜技術を用いることで,単層膜で得られる反射効率の限界を超え,Pt 単層膜の場合と比較して,Mo/Si 多層膜では約5 倍の反射効率を実現できた.

"我々は,極端紫外領域にある水星大気の共鳴散乱光を分光する極端紫外分光撮像器(EUIS:Extreme Ultraviolet Imaging Spectrometer)を水星探査計画に向け開発している.本稿では,本観測器開発の鍵となる多層膜回折格子の性能試験について報告する.結論は以下の通りである.(a)機械刻線回折格子とホログラフィック回折格子のどちらが適しているか調査し,その結果迷光の少なさという点からホログラフィック回折格子が優れていると結論した.(b)ホログラフィック平面回折格子にMoとSiのペアからなる多層膜コーティングと金コーティングを施し,回折効率を比較した.多層膜回折格子が金単層膜回折格子よりも1桁ほど効率が高いことを確認した."

A Venus orbiter to start observation in 2009 is planned by ISAS. Already at a previous meeting. Inamura (ISAS) discussed the scientific purposes. In the present talk, main optical instruments and their role for the scientific purposes are shown. The ma in purpose of this mission is to determine meteorological parameters by imaging whole night- and day-side Venus disk at various wavelengths.

According to PVO observations, a significant amount of plasmas in the dayside flows to the nightside. This fact suggests that there should be an effective loss process in the Venus ionosphere. "Clouds" is considered to be one of the candidates which are related to plasma loss process. However, the global shape, formation and the dependence on the IMF of the clouds are still unknown, because the PVO obtained only local information on plasmas. Global imaging by using EUV technique is a promising means to investigate such a study. We propose the EUV telescope onboard Venus orbitor. This instrument has a imaging capability for He I, He II, O II, and H I emissions simultaneously. In this paper, we present our motivations for conducting EUV imaging. And also, the design of the telescope is shown.

Ultra-Violet Imaging Camera (UVI) on Venus mission measures dayside airglow of Venus by using SiCCD as a detection element. UVI is specialized and used for an imaging of Venus dayside clouds to investigate the dynamics of Venus atmosphere at 〜70 km altitude. The measurement wavelengths are 275 nm and 305 nm in the absorption bands of SO_2. The spatial and temporal resolutions are 〜10 km at a distance of 3.7 Rv from Venus and 〜100 ms, which are much better than that of Orbiter Cloud Photopolarimeter on Pioneer Venus. From the observations by UVI and other Imaging Cameras with different wavelengths, we investigate the structure and dynamics of Venus clouds and atmosphere.

The purpose of the Longwave IR camera onboard Planet-C is to observe the horizontal distribution of cloud top temperature. In this paper, the science objectives, the selection criteria of observation wavelengths and the required specifications are summarized.

In this paper we present current development status of our Asteroid Multi-band Imaging CAmera (AMICA) for the Japan-US joint asteroid sample return mission MUSES-C. The launch of the spacecraft is planned around the end of 2002 and the whole mission period till sample retrieval on Earth will be approximately five years. The nominal target is the asteroid 1998SF36, one of the Amor-type asteroids. The AMICA specifications for the mission are shown here along with its ground-based and inflight calibration methods. We also describe the observational scenario at the asteroid, in relation to scientific goals.

On April 26, 1995, while Geotail was in the near-equatorial magnetotail at 13 R-E and 2300 LT, a substorm onset occurred that was documented by ground magnetograms, auroral kilometric radiation, and magnetic field and particle data from four spacecraft at and near geosynchronous orbit. Although Geotail was initially outside a greatly thinned current sheet, plasma sheet thickening associated with the substorm dipolarization quickly caused Geotail to move into the plasma sheet where it observed field-aligned earthward moving ions with velocities of 400 km/s. During the subsequent few minutes as the magnetic field became more northward, the velocities increased with particles moving increasingly into the energy range of the energetic particle experiment. These flows culminated with 1-min worth of earthward flow of 2000 km/s that was perpendicular to the northward B field. Such how, probably the largest ever detected at 13 R-E, was confirmed by the observation of an intense de electric field of 50 m V/m (0.3 megavolts/R-E). This large field is probably inductive, caused by reconnection that occurred tailward of the spacecraft, and related to the acceleration processes associated with particle injection at geosynchronous orbit. Energy and magnetic flux conservation arguments suggest that this rapid flow has a small cross-tail dimension of the order of 1 R-E. The data appear to support a simulation of Birn and Hesse [1996] which showed rapid earthward flows from a reconnection line at 23 R-E that caused a tailward expansion of a region of dipolarized flux. Subsequent to the onset, Geotail observed plasma vortices with typical velocities of 50-100 km/s that occurred in a high-beta plasma sheet with a 15-nT northward magnetic field. The vortices were punctuated by occasional flow bursts with velocities up to 400 km/s, one of which was accompanied by a violently varying magnetic field where north/south field components were as large as 30 nT and as small as -8 nT.

本論文では観測ロケットS-520-19号機に搭載したHelium Emission Monitorによるプラズマ圏ヘリウムイオンの光学的観測について報告する.HEM は多層膜反射鏡と金属薄膜フィルタ, マイクロチャンネルプレートという光学部品から構成され, ヘリウムイオンが散乱する極端紫外光に高い検出感度(∿100cps/Rayleigh, 空間分解能2.5゜)を持ち, 他の共鳴光の混入が非常に少ない直入射型望遠鏡である.観測ロケットS-520-19号機は鹿児島宇宙空間観測所から1995年1月29日午前1時に打ち上げられ, 高度220kmから観測を開始した.観測の前半は他の望遠鏡が銀河北極方向にある高温白色矮星Hz 43 の観測を行うため, HEM の視線方向は他の望遠鏡と同様に固定されていた.その後下降時の高度210-170kmの間にロケットの機軸を傾ける姿勢変更によってHEM の視線方向を移動させ, プラズマ圏ヘリウムイオンの分布を光学的に観測した.取得されたデータの解析には拡散平衡モデルを使用し, プラズマ圏ヘリウムイオンの大局的な分布の導出を行った.またロケット高度から行う光学観測には中性大気による吸収が大きく影響するため, 衛星による粒子の質量分析やISレーダによる観測データから導かれた経験モデルを用いてその効果を定量化した.その結果, 観測された散乱光の光量の変化はモデルから見積もられた光量の変化と非常によく一致していることが解り, このことから逆に電離圏上部におけるヘリウムイオンの密度とプラズマポーズ付近の温度をそれぞれ3700/cm^3および8000Kと算出することができた.近年の衛星による直接観測データと比較するとこれらの値はプラズマ圏・電離圏の典型的な値であり, さらに観測時前後の地磁気活動度が非常に低かったことも考慮に入れると今回は磁気圏全体の活動度が低い状態を観測したと考えられる.また, 観測視野を朝側地表付近に向けた時には, 昼側電離圏から He I (584A) の多重散乱光が観測された.

The acceleration process of minor heavy ions in the magnetotail reconnection layer is studied by 1D hybrid simulations. In the plasma sheet, different acceleration mechanisms are found to be operative according to the heavy ion mass, not only because of their different inertia but also because of the evolutions of different downstream states. Despite this difference, the ions, including the major protons, are accelerated up to the maximum velocity of twice the lobe Alfven velocity: the energy gain is proportional to the ion mass.