Wave motions in the atmosphere and related ionospheric phenomena

We review important studies in the field of stratosphere-ionosphere coupling, including recent studies of wave motions of planetary waves, atmospheric tides and internal gravity waves in the atmosphere. The interrelation between stratospheric sudden warmings and winter anomaly of radio absorption, a dynamical model of stratospheric sudden warmings and some production mechanisms of intensified electron density in the D region are discussed. Other topics presented are atmospheric tides in the lower thermosphere including dynamo action, and internal gravity waves, by which we intend to explain travelling ionospheric disturbances in the F ₂ region and sporadic E layer at midlatitude (wave-enhanced sporadic E). Thermospheric winds are also reviewed and wind effects on the F ₂ layer are discussed. For each atmospheric event systematic observations of suitable physical quantities with proper time and spatial intervals are desirable.     

Capability for ozone high-precision retrieval on JEM/SMILES observation

We estimate the capability of ozone (O₃) retrieval with the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) instrument attached to the Exposed Facility of the Japanese Experiment Module (JEM) on the International Space Station (ISS). SMILES carries a 4-K mechanical refrigerator to cool superconducting devices in space. Since SMILES has high sensitivity thanks to the superconducting receiver, it is expected that SMILES has ability to retrieve O₃ profiles more precisely than the previous millimeter–submillimeter limb measurements from satellites.     

用于未来月球探测的ILOM 技术现状

使用面包板模型和仿真方法,在实验室内研究月球指向就位测量望远镜(ILOM)的基本特征,如望远镜星像中心点位置精度、温度效应、倾斜以及地面震动的影响。使用这个技术预期在月球表面观测月球自转时可以达到1ms的精度。将在地面上开展测试验证观测以全面评价达到优于0.1″观测精度目标所需条件和特征。     

Simulation of optical response of retroreflectors for future lunar laser ranging

We numerically examined various retroreflectors as laser ranging targets for future missions to the Moon. The geometric conditions, such as the angle of incidence and velocity aberration, with lunar targets are much more restricted than those with most of the earth-orbiting artificial satellites. The numerical optical response simulation carried out in this study indicates that a single retroreflector with a diameter of 150–250 mm performs similar to the existing Apollo retroreflector arrays. Further, no dihedral angle is required for small retroreflectors with diameters below 150 mm for uncoated ones and below 100 mm for coated and hollow ones. Retroreflectors with larger diameters require dihedral angles of 0.20, 0.25, and 0.35 arcsec for coated, uncoated and hollow types, respectively. The objective of this fundamental study is to underlie the development of future laser ranging targets that are to be placed on the Moon.     

Ground-to-satellite laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei, central Tokyo, and a low earth orbit (LEO) satellite were jointly performed by the Japan Aerospace Exploration Agency and the National Institute of Information and Communications Technology. In 18 trials during three non-consecutive months, the satellite was acquired and tracked 61 % of the time, when clear or partly-clear conditions were predominant. The optical link was maintained for about 6 minutes when the satellite was visible in spite of the high angular velocity of the satellite. In 3 of the 18 trials, the link was not interrupted due to clouds during the six-minute transit. The failures (39% of the time) occurred when cloudy or rainy conditions were predominant. Fluctuation in the uplink received signal power was minimized by using multiple laser beam transmissions. The measured uplink and downlink bit error ratios were 10^-7-10^-4. These results demonstrate the applicability of free-space laser communication for not only geostationary earth orbit-LEO optical links but also ground-to-LEO optical links.