The thermal infrared imager (TIR) onboard the Hayabusa2 spacecraft performed thermographic observations of the asteroid 162173 Ryugu (1999 JU\(_3\)) from June 2018 to November 2019. Our previous reports revealed that the surface of Ryugu was globally filled with porous materials and had high surface roughness. These results were derived from making the observed temperature maps of TIR using a projection method onto the shape model of Ryugu as geometric corrections. The pointing directions of TIR were calculated using an interpolation of data from the SPICE kernels (NASA/NAIF) during the periods when the optical navigation camera (ONC) and the light detection and ranging (LIDAR) observations were performed. However, the mapping accuracy of the observed TIR images was degraded when the ONC and LIDAR were not performed with TIR. Also, the orbital and attitudinal fluctuations of Hayabusa2 increased the error of the temperature maps. In this paper, to solve the temperature image mapping problems, we improved the correction method by fitting all of the observed TIR images with the surface coordinate addressed on the high-definition shape model of Ryugu (SFM 800k v20180804). This correction adjusted the pointing direction of TIR by rotating the TIR frame relative to the Hayabusa2 frame using a least squares fit. As a result, the temperature maps spatially spreading areas were converged within high-resolved \(0.5^\circ\) by \(0.5^\circ\) maps. The estimated thermal inertia, for instance, was approximately 300\(\sim\)350 Jm\(^{-2}\)s\(^{-0.5}\)K\(^{-1}\) at the hot area of the Ejima Saxum. This estimation was succeeded in case that the surface topographic features were larger than the pixel scale of TIR. However, the thermal inertia estimation of smooth terrains, such as the Urashima crater, was difficult because of surface roughness effects, where roughness was probably much smaller than the pixel scale of TIR.

Hayabusa2航天器上的红外热像仪（TIR）对小行星162173 Ryugu（1999 JU \（_ 3 \）进行了热成像观察）从2018年6月至2019年11月。我们以前的报告显示，龙宫的表面在全球范围内充满多孔材料，并且表面粗糙度较高。这些结果是通过使用投影方法在Ryugu的形状模型上绘制观测到的TIR的温度图作为几何校正得出的。在执行光学导航摄像机（ONC）和光检测与测距（LIDAR）观察期间，使用来自SPICE内核（NASA / NAIF）的数据插值来计算TIR的指向方向。但是，如果不使用TIR进行ONC和LIDAR，则观察到的TIR图像的映射精度会降低。此外，Hayabusa2的轨道和姿态波动增加了温度图的误差。本文为解决温度图像映射问题，我们通过将所有观察到的TIR图像与Ryugu的高清形状模型（SFM 800k v20180804）上解决的表面坐标拟合来改进校正方法。此校正通过使用最小二乘拟合相对于Hayabusa2框架旋转TIR框架来调整TIR的指向方向。结果，将温度分布图的空间分布区域收敛于高分辨率的区域。\（0.5 ^ \ CIRC \）由\（0.5 ^ \ CIRC \）映射。估计的热惯量，例如，约为300 \（\ SIM \） 350 JM \（^ { - 2} \）小号\（^ { - 0.5} \） ķ \（^ { - 1} \）在江岛萨克森邦的热区。如果表面形貌特征大于TIR的像素比例，则此估算成功。但是，由于表面粗糙度的影响，光滑的地形（如浦岛陨石坑）的热惯性估计很困难，因为粗糙度可能比TIR的像素尺度小得多。