Crater Ray Explorer ( <scp>CRAYEX</scp> ): Toolkit to evaluate the spallation expanse of rayed craters on lunar surface

Abstract Among the various impact features on the Moon, the ejecta—especially the distinct ray systems—are particularly noteworthy. Impact craters formed during the Eratosthenian (3.16–0.8 Ga) and Copernican (0.8 Ga to present) periods tend to preserve these ray systems, although later impacts can obscure rays from older craters. In this study, a faster approach for ejecta ray delineation is proposed through a toolkit named CRAYEX (Crater RAY EXplorer). An image‐based methodology is applied to trace crater ejecta rays, taking advantage of albedo variations to discern both younger and older rayed ejecta material. The efficiency of this toolkit was demonstrated through a preliminary study of 10 representative craters distributed across both mare and highland terrains. To assess accuracy, the reliability of the thresholding method was tested by comparing Otsu, Multi‐Otsu, Li, Yen, inverted Otsu, and F1‐optimized thresholds. Among these, Otsu's method—based on the minimization of variance—proved to be the best approach for providing accurate segmentation results in remotely sensed images, yielding nearly optimal F1 measures. Using this approach, threshold values ranging from 0.4636 to 0.5118 were found to be effective for ejecta delineation from optical maturity (OMAT) images. Through iterative processes employing established methods (such as CraterPy for crater extraction and density slicing for intensity‐based segmentation), CRAYEX successfully delineated rayed ejecta materials with observed F1 scores ranging from 0.4 to 0.6. Thus, CRAYEX paves the way for a more comprehensive exploration of lunar impact craters.