Lunar exploration rovers must traverse loose soil when they explore ground like lunar surface actually. If the rovers traverse loose soil, some traces of the wheels are made after traversing. This paper focuses on theses traces drawn on loose soil. If the pictures of the traces are given by the camera installed the rovers, we can estimate slip ratio by using them. There is the difference of brightness between with and without the traces of the wheels. The traces are detected by using these differences of brightness digitally. This paper proposes the method to estimate slip ratio using the differences of brightness of the traces of the wheels. We furthermore understood the effective of this scheme from running experiments.
