3D mapping by active stereo sensor on sampling mission of asteroid surface

This paper discusses a 3D mapping technology using an active stereo sensor based on a surface sampling. In recent years, various sampling missions such as asteroids and satellites have been actively investigated. In these missions, a wide range of mapping is an essential aspect of obstacle detection and the best selection for the sampling from the unknown surface. In conventional methods, Flash LIDAR and stereo vision are widely used, however, Flash LIDAR only gets information about the distance and cannot determine the object. Furthermore, because this method is specialized for long distances, the accuracy tends to be low in the short distance such as within 1 m. The second way is stereo vision. In this way, it is necessary to extract several feature points. Therefore, because the entire surface is covered by the regolith, it is impossible to measure. In addition, the performance is also greatly dependent on sunlight conditions. For this reason, an auto regulatable active stereo is suggested, because it can adapt to any surface condition. In this the auto regulatable active stereo, two methods of a local binarization and a color modulation are proposed to keep a high mapping accuracy. First, the local binarization can correspond to the environment on which the shade and sunshine areas exist at the same time. Second, the color modulation can provide a stable measurement due to not depending on the surface color. These performances are evaluated by means of experiments conducted taking into consideration several sunlight and surface conditions. The experiment results confirmed that the accuracy is higher than other TOF(time of flight) sensors. Furthermore, the mapping can be made under strong sunlight and the environment of high gray scale of sand. Therefore, this 3D mapping method is expected to maintain high accuracy in an unknown environment such as the sampling mission.