Development of infrared imaging devices for the observation of planetary atmosphere

金星大气层在海拔70公里以下的运动由于受到厚厚的云层的阻挡而没有被研究过。但是，在红外线穿过厚厚的云层之后，观察低层云层和金星表面的运动成为可能。我们的目标是利用金星的云层和表面作为示踪剂，通过环绕金星的航天器上的红外摄像机来观察大气层的运动。这种方法将是世界上第一个。在本次研究中，我们开发了红外相机的成像装置和光学系统，可以用于金星的探测，也可以用于未来对其他行星的探测。在近红外（1 ~ 3μm）和中红外（8 ~ 12μm）两个波段的成像器件和光学系统的研制尤为重要。前者对应于云层底部（50-70km高度）的发射，使我们能够观测大气的运动。相反，后者对应于云层顶部的热辐射。因此，在近红外区域使用PtSi肖特基器件，在中红外区域使用测热计阵列作为抗辐射成像器件是最好的。肖特基装置需要冷却到60K，一级斯特林冷却器被证明能够完成它。这一研究与天文领域红外观测航天器的发展较为接近。在这一领域，通过冷却红外设备将热噪声降至最低的技术已经得到了改进，用于观测遥远的、暗的恒星或年轻的行星系统。但是，如果安装在行星探测航天器上，它将长时间暴露在辐射和比地面天文观测更严酷的高温条件下。在这个时候，需要研制适用于行星轨道器的红外装置，而且研制成功了。

The motion of the atmosphere of Venus at the altitude of less than 70km has not been studied because it is prevented by the thick cloud layer. But it became possible to observe the motion of lower clouds and surface of Venus after infrared ray turned out to pass through the thick cloud layer. We aimed at the observation of the motion of the atmosphere using Venusian clouds and surface as tracers by the infrared camera in the spacecraft orbiting around Venus. This approach will be the first one in the world.In this study, we developed the imaging device and optical system for infrared camera which can be used in the exploration of Venus and also future exploration of another planet. It is especially important to develop the imaging device and optical system in two bands, near-infrared region (1-3μm) and mid-infrared region (8-12μm). The former corresponds to the emission from the bottom of clouds (at the altitude of 50-70km), which enables us to observe the motion of the atmosphere. On the contrary, the latter corresponds to the thermal radiation from the top of clouds. As a result, it turned out to be best to use PtSi Schottky device in near infrared region and bolometer array in mid-infrared region as radioresistant imaging device. Schottky device needs to be cooled to 60K, and one stage Stirling cooler proved to be able to accomplish it.This research is relatively close to the development of infrared observation spacecraft in astronomical field. In this field, the technology which reduces a thermal noise to the minimum by cooling the infrared device has been improved for the observation of far, dark stars or young planetary system. But, if it is installed to planetary exploration spacecraft, it will be prolonged exposure to the radiation and also the much harsher heat condition than ground-based astronomical observations. In this time, the development of the infrared device suitable for the planetary orbiter was needed, and it was sufficiently achieved.